Great video. All the information one needs to know to compression check an outboard without any fluff. Short educational videos are Greatly appreciated. Thank you.
Good for you! There is an ever-increasing need for skilled marine mechanics, and there is currently an industry initiative to expand available programs and training. Not to mention many grants to help with expenses and pretty much guaranteed jobs after graduation. Check out www.abycfoundation.org/ and www.boatus.com/expert-advice/expert-advice-archive/2019/april/scholarships-in-marine-studies-and-technology for helpful resources. I also recall MarineMax was starting its own training program a couple years ago where students are considered employees and get paid while they learn. Wishing you all the best!
MAKE SURE YOU HAVE FULL THROTTLE AND FULL CHOKE ON!!!! I have personally seen 30% psi difference with these two conditions the other way (low throttle, choke off). This is especially true on older outboards I work on (60's and 70's).
The test can be done both hot and cold for a comparison. The cylinder hose threaded end needs to be checked to make sure it is the correct length. The throttle should be set at WOT Fully charged batteries and a battery charger should be connected to keep cranking as consistent as possible. An equal number of revolutions across the cylinders.
I see this video is older. I am a newbie to boating, and am looking at a 1999 cobia cc w/150 ox66 saltwater series II. Questions? Should I check even if she cold starts immediately, or check to assure motor is good compression . Also, any damage with fuel pump disconnected ? BTW, ENJOY BOAT US. AM MEMBER, LOTS OF GOOD INFO, AND FREE COURSES!
Thanks for the question, Dave. Speaking both as a boater with many years’ experience and as a boat surveyor, my personal take is that a compression check, while useful, is often unnecessary. There are so many factors that come into play here: How old is the engine, how many hours does it have on it, has it been regularly serviced and will it make the manufacturers recommended maximum revolutions? Providing the engines meet all the criteria and perform as the manufacturer indicates in the technical bulletin or owner’s manual then all will most likely be well and a compression check unnecessary. Having said all of that, I see that the engines you refer to are two stoke making access to the spark plugs much easier as they are easily removed from the cylinder heads without disassembly of any other parts to gain access and remove the plugs. This makes a difference, and also makes taking a compression test that much simpler, so I see no reason why it should not be done. Remember that a compression check must be carried out when the engines are warm - a cold engine will give false high readings - and all readings should be within about 10% of each other. If one is much lower than the rest then this could be indicative of s problem that needs further investigation. You may find the following link helpful. www.boatus.com/expert-advice/expert-advice-archive/2016/april/checking-compression-on-an-outboard-engine
@@joewall1416 My bad, Joe. Thanks for pointing this out; you are quite correct, it should be 10% not 10 psi. Having said that, oftentimes the difference will be no greater than 10 psi between cylinders. Sorry for the confusion. I've updated my original response to Dave.
Hi.. Thank you for the informative video. I learned a lot especially the part of removing all spark plugs before performing the compression test. I do however, have a question regarding wear and tear and life of the motor. I know the first reading is the benchmark, but how do I know that reading is within acceptable levels? Thank you!
Hi Marlon. Great question! A compression test is a comparative test. We're less concerned about the actual reading than we are with the cylinders being within approximately 10% range of each other.
Hi Yoel. The readings should all be within 10% of each other. The readings themselves aren't that important -- it's whether they're similar. Thanks for the question!
Great video and great explanation. I’m trying to buy a boat with a 150hp 4s Yamaha. Yesterday I took a tech to run this test, one cylinder was 150 others: 160 and third was 150, in case 4th we have no pressure but the owner said this boat hasn’t Been started for more than a year so maybe this can explained the cause. What I’m worried about is because the tech didn’t took off the fuse of the fuel pump and the test was made with the first start of the motor so it wasn’t hot. I really like the boat I’m trying to buy. Hope to receive any advice. Already gave you thumbs up and just subscribed to your channel . Thanks
Thanks for the like and subscribe, Raul. While we can't make specific recommendations because we're not there on site, we always suggest getting any boat (new or used) looked at by a qualified SAMS or NAMS surveyor. It's money well spent and can save you a lot of time, money, hassle, and heartache down the road. You're right to be concerned about the compression test results, and it would be good to get more info -- not just taking the owner's "guess." If you already took it to a trusted tech, I'd want to know what they think about the results. Even if you choose not to have a survey done, getting that boat out for a test ride before any money exchanges hands is important. If the owner isn't willing to do that, it might be a red flag. A couple other important things: Be sure you get EVERYTHING in writing (via a sales contract) including price, what's included with that price (electronics, trailer, etc.), any repairs the seller agrees to make, any known problems, etc. For more boat-buying tips from BoatUS, check out the articles here: www.boatus.com/expert-advice/boats-and-tow-vehicles/buying-and-selling-advice. It sounds like you have some concerns. Don't ignore them. And be sure to ask specific questions. The seller isn't required to reveal anything you haven't asked about, but he must disclose any issues if you do ask. Hope this helps and best of luck! Let us know how it turns out.
It depends on the outboard and its individual systems, James. In many cases, pulling the kill switch will accomplish the same thing. We'd suggest going by the engine manufacturer's recommended procedure, and if you can't identify it, ground the leads to be safe.
Hi I have a 2001 90 hp mercury. Last oil change was 2 years ago I do a lot of winter trolling. Last time I checked my oil level it was a half inch high. When I drained the oil milky water came out of the crank case. I would say no more than 6 ounces. I've read that these motors build up internal condensation. Before I confirm this I want do a compression test. Have you ever seen this problem before? This is my first time servicing this motor. I usually take it to a shop.
Thank you for the question, Pacoloco. Six ounces of water sounds like quite a lot, and I suspect that this may be more than simply condensation. Water in the oil could come from a number of sources, such as a leaking head gasket or worn seal - both of which will require the services of a trained outboard mechanic. Although you do not say how many hours are on the engine, I question why you believe that you need to do a compression check. This has nothing to do with water in the oil, which is a separate issue entirely. A compression check can provide a useful insight into the wear in an engine but often is not required unless other issues such as lack of power or a misfire is noted. A compression check is just one of a battery of engine checks that can be carried out to try and determine a problem with a motor. Of far greater concern to me is the water in the oil, and I would encourage you to get the engine checked out at a certified repair facility before you use the motor again.
I’ve see 2 problems in this video. First for safe you should have the spark plug test connected to the wires ( you don’t want to get zapped while doing it ), also you should have the throttle in WOT for accuracy readings. Good luck
Thanks for your comment, Cesar. Cranking over the engine while performing a compression test introduces gasoline into the cylinders. You don’t want the high tension spark plug leads connected to anything that may produce a spark and potentially ignite any unburned fuel close by. Secondly, the disconnected spark plug leads are well shielded by the spark plug push-on connectors, so the risk of shock is very slight especially if the ends of the leads are tucked well out of the way while carrying out the compression test. To your other point, it’s certainly possible to have the throttle in the wide-open position while performing a compression test, and I know mechanics who do this. The theory is that this introduces more air into the cylinders and thus gives a more accurate reading. However, much of the value in any compression test is the comparative readings between each cylinder. Opening the throttle may add a couple of extra pounds to the peak readings but it won’t alter the fact that one cylinder may have a lower reading relative to the others. That said, we stress that you should always follow the manufacturer's recommendations. If you're not sure, invest in a maintenance manual for your specific engine. It's money well spent.
BoatUS That’s Right, while cranking the engine over it introduces gas into to engine ( good thing that you disabled the fuel pump by removing the fuse ) however having the spark plug leads hanging closed to the block without any protection is a little danger, the high current is looking for a ground and the engine block is a good source of it, most of the spark plug tester are safe to use.
Not to mention, unless I am mistaken, it can do damage to the ignition system having juice going to the unattached plug wires. I’ve always disabled power to the plug wires and fuel pump, if the pump runs of power. Either way you don’t want fuel or spark live during a compression test.
@@boatus I was wondering how many comments I'd read through before finding the "you're doing it wrong" trolls. If it wasn't for UA-cam videos, I can't help but wonder what these guys would be doing, and who they'd be doing it to. This was a great video, and while there are always more than one way to skin a cat, you did nothing wrong....
@@atomicslam1589 Thanks, Atomic. We are always happy for the additional input, which is usually very helpful, because, as you very rightly point out, there are often many acceptable ways to do things--and we do learn some great tips from our viewers and readers. But, yes, we do sometimes wonder why folks who clearly already know so much are watching our how-to videos. 🤷♀️
2001 Evinrude 4stroke, 3 cyl. Had very weak telltale and oil temp alarm going off. Replaced oil temp sensor and new water pump. Telltale stream is good, oil overheat alarm still goes off but take a good 15 min. However, new and crazy problem is water now flowing into all 3 carbs??? How do determine cause?
Not good at all, Water Monkey, and not something we feel comfortable tackling as a DIY. We recommend finding a good mechanic pronto. Good luck, and let us know how it turns out.
I just tested my 1991 Evinrude "BEFORE" watching this video. My cylinders are all with 10% of one another, but...I did not remove all the plugs at once and the motor was cold. Should I re-check using your method? Thank You
Thanks for the question, Steve. As we mentioned in the video, the compression should be checked with the engine warm. This gives the pistons a chance to expand in the bores and will give a more accurate reading. Always check the compression with the plugs removed, this allows the engine to spin over easily, places far less strain on the starter motor, and perhaps most importantly, ensures that the engine will not start unexpectedly. I’m glad to hear that the readings are all within 10% of each other, and although I doubt that there is anything out of whack with your motor, it would probably be best to use the method we described in the video.
Hello and thank you for this video. I am in the market to buy a used outboard 85 HP Mercury motor for my fishing boat and it has not been started in over 10 years. If the motor can't be warmed up because it won't start how would you do a compression check? Thanks in advance.
Hi Omar. For a compression test to mean anything, the motor needs to be warmed up first. An outboard that hasn't started in 10 years is likely to need a number - a large number - of fixes before it can be started. The litany of items to replace is too long to address here, but we wouldn't recommend tackling this alone; having a professional look at the motor is in order for sure. Good luck!
Hi Jess and thanks for your question. Unfortunately we're not able to answer questions like these as we're not familiar with every engine out there. We recommend taking a look at the owner's manual, available through Yamaha. Just plug in the info from your engine here: yamahaoutboards.com/owner-center/owners-manuals. I'm not sure if this is the correct manual, but it may give you a place to start: www.manualslib.com/manual/559932/Yamaha-F250.html?page=78. Alternatively, reach out to Yamaha's customer service. An online search shows some videos and articles as well. Good luck!
Our compression test was good, however it really seems that after our engine warms up we are dropping a cylinder, the power will definitely lower and will try to surge periodically. Is this possible with good readings?
Thanks for your question, Shannon. Without seeing the engine in person, I can only offer general advice here. Engine compression should only be checked once the engine is warmed up to normal operating temperatures. This is because hot components will expand and have a bearing on the readings taken. A cold engine will give readings higher than hot engine. Assuming that the compression checks are normal, I would suspect something else, which, from your brief description, leads me to believe that this is most likely a fuel issue. My reasoning is that compressions do not change from moment to moment and cause surging. If your engine has fuel injection, it may well be that one of the injectors is partially blocked and requires service or replacement. Or it could be something as simple as a worn-out fuel filter that needs replacing. I would thoroughly check all the fuel system components: hoses, filters, connections, and injectors or carburetors. If you are unable to do this work yourself, I would seek the services of a qualified technician. Hope this helps!
do you need water running through the engine.....My manual says, don't crank without water. Should the starter be disconnected ? More I utubes I watch, the more confused I get.
Thanks for the great question, Livio. You do need a water source any time the engine will run, so many people say to make sure it has a sufficient water supply "before you crank it over," which is correct. However, since you remove the spark plugs for this procedure (performing a compression test), there's no chance of the engine firing. Thus no heat is created, and no cooling water is required. The starter, you don't need to worry about. Hope this helps clarify things.
@@boatus sure does....just heli coiled a bolt on the cylinder head...all torqued to 20lbs....cleaned and lubricated cylinders....now will compression test....throttle and choke wide open....fingers crossed
Tnx for the informative video ,I have a question plz, whats the normal pressure for yamaha 85hp mix oil and fuel engine and is there a difference in the air pressure gage if is stander engine or 50 fixed or 25 fixed ?👋
Thanks for the question, Sam. If I understand you correctly, you are wondering what is the compression pressure that you should see on the gauge when you conduct a compression check. The pressure should be somewhere around the 125 psi mark but may be slightly more or less. What is more important is the comparison between the cylinders. Check each in turn and note the readings which should show a variation of no more than about 10 psi between cylinders. If one is significantly lower, further investigation will be required as this could be indicative of a stuck or worn valve, piston and bore wear, or some other issue.
Thanks for the question, Jared. The actual compression number is dependent on several factors: the age of the engine, the type, whether the valves and valve guides are in good condition, and so on. Check the compression when the engine is hot; a cold engine will give false high readings. I would expect the numbers to be in excess of 100 psi with each of the cylinders within 10% of each other.
Hi sir. Good day. Can i ask about our yamaha 115 four stroke. If i will give rpm. Engine is good. But if iengaged the gear. There is no speed.. pls help
Hi Jayden. Thanks for the question. It's not about the numbers themselves; the critical part is ensuring that the difference among all the cylinders is within 10%. Hope this helps.
Thanks for the follow-up, Jayden. In our experience, most manufacturers won't cite an "official" compression number for their outboards. And you can't put any across-the-board number on it because all engines are designed differently. Our guess is that if you're getting only 50 psi readings, even if they are within 10% of each other, the engine isn't going to run. (If it does, the issue may be with your tester.) Unfortunately, I'm not sure we can be of further assistance without being on site, and your best bet is to consult manufacturer recommendations and/or a trusted mechanic. If you are having a specific issue, you might consider sending your question along with any pertinent info (and photos if applicable) about the specific engine to magazine@boatus.com and we can forward it to our technical editor for possible answer in a future issue of BoatUS Magazine.
@@boatus thanks very much! I don't have an issue now, but just learning about all the various things, and this was a confusing detail that seems to be overlooked. Maybe because it's not very relevant! But I really appreciate your responses.
Thanks for the question, Jordan. Cooling water is only required while the engine is actually running. The engine is not started when conducting a compression test so, no, you do not need the muffs on the engine. Also, a common mistake when conducting a compression check is not removing all the spark plugs. Removing the plugs does two things: 1. It ensures that the engine cannot be started, and 2. there will be no compression allowing the motor to spin over on the starter easily.
Good question, Gary. You are going to need to use the starter to perform the compression check. As you will have removed all the sparkplugs and disconnected the HT leads to the plugs, the engine can't start.
@@boatus On that motor, if you had used a remote starter switch (www.google.com/search?q=remote+starter+switch&oq=rfemote+starter&aqs=chrome.2.69i57j0l5.8468j0j7&sourceid=chrome&ie=UTF-8) between the battery positive connection at the starter solenoid and the brown wire next to it on the same solenoid, you would not have needed to remove the 15 amp fuse for the fuel system or worried about the ignition firing as long as the key was off and or the emergency stop lanyard was disconnected. At that point, all you would be doing is cranking the pistons, crank and such with no other motor functions. I'm glad to see you showed the technician watching the compression reading as they were taken as that is an often forgotten important component to taking a proper compression reading. Paul Murphy, Yamaha Master Tech.
I was always under the impression you should disable the ignition system so you don’t damage it if the plugs are disconnected and not grounded. You really only want power going to your starter.
HI Dan. Thanks for the question. For a compression test, you literally only need to crank the engine over one or two time and this is insufficient time to damage the water pump impeller. So go ahead and all will be well if you follow the instructions in the video.
Thanks for the question! In your case, it's probably not necessary. A compression check is simply one check that engine surveyors and interested owners can do on their engines. A compression check will give an indication of “blow by” of the rings and valves. This is unlikely to occur on an a nearly new engine and I would say that it is unnecessary, unless there is some other fault with the engine such as rough running or excessive oil use. A compression check can be useful at times but a more useful check would be to get the engine to a local authorized service center that services your make of engine and get them to plug the engine’s ECM into the diagnostic computer. This will show any fault codes and the technician will be able to tell a lot about the health of the engine from this simple check, certainly far more than doing a compression check in isolation.
Your mechanic is correct, Bill. The spark plug high tension leads should all be grounded using a spark checker. Without being grounded, power pack/ECM damage could occur.
Thanks for the question, Joseph. This could be so many things: Is the battery flat, are the high tension leads in good shape, is the ECM (engine control module) faulty? There are so many possibilities that it is impossible to give an answer without seeing the engine in person. The best thing I can suggest is that you entrust your engine into the hands of certified outboard mechanic who has the tools to diagnose and correct this problem. You do not say what year your engine is, but the newer engines can be connected to a computer and the mechanic can then download the fault codes, which will go a long way in finding out what the problem is.
Hi Tom. Happy to answer any questions you have, but they seem to have gotten cut off. Feel free to edit the original or reply if you still want to ask them.
siiiii genial ya que mi motor es un 90 suzuki de pronto ahdecer lo mismo y al conprar un uasado tambien ahde dar la nisma lectura de ub dies por siento gracias
Thanks for the question, Cheryl. You should not need an adapter. As you will see, there is a rubber hose, usually about a foot long, in your kit that has a press fitting one end that goes into the gauge and a screw that goes into the plug hole. Before connecting the hose to the gauge, you should be able to attach the threaded end to into the plug hole by twisting the hose. The hose only needs to be hand tight. Before conducting a compression test, make sure to remove all the plugs from the engine. This prevents any inadvertent starting and makes it easier for the starter to crank the engine over.
Hello, thanks for your question! There is no specific compression tester for outboard motors. You can find suitable compression testers at places like NAPA or Autozone. Since it’s a tool that you need infrequently, you may find that you can rent one from either of these outlets.
I got my most recent compression gauges from Amazon for about $20 with a carrying case and an assortment of adapters and fittings a year or 2 ago and I've used the crap out of them. That's where I'd look.
Thanks for the question. The size of the threads varies depending on the make, size, and age of the motor. Older motors used either a 21mm or 22mm thread and required a 13/16 or 3/4 inch socket to remove them respectively. However, most modern engines us a 16 mm plug and require a 5/8 deep-well plug socket to remove them.
Remember what the tech told us between 0:30 and 1:05 in the video. The key thing to look for isn't one specific number or another, but that all of the cylinders are within 10-percent of one another. Different gauges can vary a bit and elevation is also a factor, which is one of the reasons why looking for the different cylinders to match up is what you really want to look for.
You shouldnt have a 0 reading on one whole bank of the engine, check you threaded the tester correctly otherwise the only thing I can think of is if it's a 4 stroke you have valve blowby but I have never heard of that happening to a whole bank
Thanks for the question. If you have no compression it can only be down to a few things. Assuming that you have no compression at all on one side of the engine, I would suggest that you have holes in the pistons or the piston rings are no longer doing their job and have totally failed, often due to the engine severely overheating at some time. Another possibility is that the cylinder head gasket has failed. These engines were last made in 2000 and although I don't have much knowledge of these engines in particular I would imagine that it should be possible to buy spare parts. However, you may want to get a qualified outboard technician to give the engine the “once over” before you go spending a lot of money on it, as the cost of repairs may well be far in excess of what the engine is worth.
@@boatus I’m sorry was in a bad mood that day and should’ve kept to the if I don’t have anything good to say than should’ve kept my mouth shut., thanks for the video non the less BUT the nitpicks I had: Said remove all spark plugs so engine doesn’t fire and cylinder gets more air. Shouldn’t fire because ignition system should be properly taken care of by either grounding spark plugs or cranking with safety lanyard disconnected or risk damaging ignition circuit which was never mentioned. Main reason to pull spark plugs is to make it easier on starter to turn over engine due to only having resistance on cylinder being tested. Adjacent cylinders have no influence on air of cylinder being tested but throttle body position does on a 4 stroke so it’s important to open and hold throttle body to its most open position while cranking for most accurate readings. Fuel in cylinders will not wash out readings as it is vaporized into a gas by the time it reaches the cylinder anyways. How do you think ouboards without a fuel pump(ie carburetion) are tested. Which many people coming for a compression testing video will be inquiring about. “Certification” credentials are nothing but check boxes for appearance and by no means signify expert subject matter
Can anyone out there tell me WHY you need a boat? One reason? Anyone? Your hobby of polluting our freshwater supplies is not more important than my grandchildrens future! Private ownership of boats should be banned. Bernie Sanders 2020!
Is Bernie going to be alive in 2020? While boats do pollute. They are just a small fraction of the reason for pollution. Take a look at how your battery in your phone is made. Or better yet how nuclear power is running your computer. Boats dont have place on a big list of reasons why water and air is getting polluted. Nice try. And for your sake I hope you dont have anything gas powered (lawnmower, car or bus ect). Because in your words, you are also part of the problem.
Great video. All the information one needs to know to compression check an outboard without any fluff. Short educational videos are Greatly appreciated. Thank you.
Thanks for watching, Jon, and we appreciate the feedback!
nice video @BoatUS i am thinking about going to school for marine mechanics might as well since i love fishing so much
Good for you! There is an ever-increasing need for skilled marine mechanics, and there is currently an industry initiative to expand available programs and training. Not to mention many grants to help with expenses and pretty much guaranteed jobs after graduation. Check out www.abycfoundation.org/ and www.boatus.com/expert-advice/expert-advice-archive/2019/april/scholarships-in-marine-studies-and-technology for helpful resources. I also recall MarineMax was starting its own training program a couple years ago where students are considered employees and get paid while they learn. Wishing you all the best!
MAKE SURE YOU HAVE FULL THROTTLE AND FULL CHOKE ON!!!! I have personally seen 30% psi difference with these two conditions the other way (low throttle, choke off). This is especially true on older outboards I work on (60's and 70's).
Thanks for the advice, David. This is useful for old two-strokes.
WHAT ????!!!!!!??????.....does it need to be in the water ? Cuz thats gonna be a problem.
The test can be done both hot and cold for a comparison.
The cylinder hose threaded end needs to be checked to make sure it is the correct length.
The throttle should be set at WOT
Fully charged batteries and a battery charger should be connected to keep cranking as consistent as possible.
An equal number of revolutions across the cylinders.
Thanks for watching!
You said the engine needed to be hot what if it can't be warmed up because it won't start. How would you do a compression check
I see this video is older. I am a newbie to boating, and am looking at a 1999 cobia cc w/150 ox66 saltwater series II. Questions? Should I check even if she cold starts immediately, or check to assure motor is good compression . Also, any damage with fuel pump disconnected ?
BTW, ENJOY BOAT US. AM MEMBER, LOTS OF GOOD INFO, AND FREE COURSES!
Thanks for the question, Dave. Speaking both as a boater with many years’ experience and as a boat surveyor, my personal take is that a compression check, while useful, is often unnecessary. There are so many factors that come into play here: How old is the engine, how many hours does it have on it, has it been regularly serviced and will it make the manufacturers recommended maximum revolutions? Providing the engines meet all the criteria and perform as the manufacturer indicates in the technical bulletin or owner’s manual then all will most likely be well and a compression check unnecessary.
Having said all of that, I see that the engines you refer to are two stoke making access to the spark plugs much easier as they are easily removed from the cylinder heads without disassembly of any other parts to gain access and remove the plugs. This makes a difference, and also makes taking a compression test that much simpler, so I see no reason why it should not be done. Remember that a compression check must be carried out when the engines are warm - a cold engine will give false high readings - and all readings should be within about 10% of each other. If one is much lower than the rest then this could be indicative of s problem that needs further investigation.
You may find the following link helpful. www.boatus.com/expert-advice/expert-advice-archive/2016/april/checking-compression-on-an-outboard-engine
@@boatus The video says 10% of one another, when comparing compression numbers and your reply says 10 psi. Which is correct?
@@joewall1416 My bad, Joe. Thanks for pointing this out; you are quite correct, it should be 10% not 10 psi. Having said that, oftentimes the difference will be no greater than 10 psi between cylinders. Sorry for the confusion. I've updated my original response to Dave.
@@boatus Thanks for the quick response and clarification!
Joe
Hi.. Thank you for the informative video. I learned a lot especially the part of removing all spark plugs before performing the compression test. I do however, have a question regarding wear and tear and life of the motor. I know the first reading is the benchmark, but how do I know that reading is within acceptable levels? Thank you!
Hi Marlon. Great question! A compression test is a comparative test. We're less concerned about the actual reading than we are with the cylinders being within approximately 10% range of each other.
Understood. Thank you!
Is it not more of 10% difference between the highest and the lower reading or10 PSI units?
Hi Yoel. The readings should all be within 10% of each other. The readings themselves aren't that important -- it's whether they're similar. Thanks for the question!
Great video and great explanation. I’m trying to buy a boat with a 150hp 4s Yamaha. Yesterday I took a tech to run this test, one cylinder was 150 others: 160 and third was 150, in case 4th we have no pressure but the owner said this boat hasn’t Been started for more than a year so maybe this can explained the cause.
What I’m worried about is because the tech didn’t took off the fuse of the fuel pump and the test was made with the first start of the motor so it wasn’t hot.
I really like the boat I’m trying to buy. Hope to receive any advice.
Already gave you thumbs up and just subscribed to your channel . Thanks
Thanks for the like and subscribe, Raul. While we can't make specific recommendations because we're not there on site, we always suggest getting any boat (new or used) looked at by a qualified SAMS or NAMS surveyor. It's money well spent and can save you a lot of time, money, hassle, and heartache down the road. You're right to be concerned about the compression test results, and it would be good to get more info -- not just taking the owner's "guess." If you already took it to a trusted tech, I'd want to know what they think about the results. Even if you choose not to have a survey done, getting that boat out for a test ride before any money exchanges hands is important. If the owner isn't willing to do that, it might be a red flag. A couple other important things: Be sure you get EVERYTHING in writing (via a sales contract) including price, what's included with that price (electronics, trailer, etc.), any repairs the seller agrees to make, any known problems, etc. For more boat-buying tips from BoatUS, check out the articles here: www.boatus.com/expert-advice/boats-and-tow-vehicles/buying-and-selling-advice.
It sounds like you have some concerns. Don't ignore them. And be sure to ask specific questions. The seller isn't required to reveal anything you haven't asked about, but he must disclose any issues if you do ask. Hope this helps and best of luck! Let us know how it turns out.
Thanks. It was well done.
Thanks for watching, MG. Glad you found it useful!
Would you recommend grounding off the sparkplug wires to avoid doing damage to the electrical system when performing a compression test? Thanks.
It depends on the outboard and its individual systems, James. In many cases, pulling the kill switch will accomplish the same thing. We'd suggest going by the engine manufacturer's recommended procedure, and if you can't identify it, ground the leads to be safe.
Hi I have a 2001 90 hp mercury. Last oil change was 2 years ago I do a lot of winter trolling. Last time I checked my oil level it was a half inch high. When I drained the oil milky water came out of the crank case. I would say no more than 6 ounces. I've read that these motors build up internal condensation. Before I confirm this I want do a compression test. Have you ever seen this problem before? This is my first time servicing this motor. I usually take it to a shop.
Thank you for the question, Pacoloco. Six ounces of water sounds like quite a lot, and I suspect that this may be more than simply condensation. Water in the oil could come from a number of sources, such as a leaking head gasket or worn seal - both of which will require the services of a trained outboard mechanic.
Although you do not say how many hours are on the engine, I question why you believe that you need to do a compression check. This has nothing to do with water in the oil, which is a separate issue entirely. A compression check can provide a useful insight into the wear in an engine but often is not required unless other issues such as lack of power or a misfire is noted.
A compression check is just one of a battery of engine checks that can be carried out to try and determine a problem with a motor. Of far greater concern to me is the water in the oil, and I would encourage you to get the engine checked out at a certified repair facility before you use the motor again.
Great video, thanks for the info.
Thanks for watching!
I’ve see 2 problems in this video. First for safe you should have the spark plug test connected to the wires ( you don’t want to get zapped while doing it ), also you should have the throttle in WOT for accuracy readings. Good luck
Thanks for your comment, Cesar. Cranking over the engine while performing a compression test introduces gasoline into the cylinders. You don’t want the high tension spark plug leads connected to anything that may produce a spark and potentially ignite any unburned fuel close by. Secondly, the disconnected spark plug leads are well shielded by the spark plug push-on connectors, so the risk of shock is very slight especially if the ends of the leads are tucked well out of the way while carrying out the compression test.
To your other point, it’s certainly possible to have the throttle in the wide-open position while performing a compression test, and I know mechanics who do this. The theory is that this introduces more air into the cylinders and thus gives a more accurate reading. However, much of the value in any compression test is the comparative readings between each cylinder. Opening the throttle may add a couple of extra pounds to the peak readings but it won’t alter the fact that one cylinder may have a lower reading relative to the others.
That said, we stress that you should always follow the manufacturer's recommendations. If you're not sure, invest in a maintenance manual for your specific engine. It's money well spent.
BoatUS That’s Right, while cranking the engine over it introduces gas into to engine ( good thing that you disabled the fuel pump by removing the fuse ) however having the spark plug leads hanging closed to the block without any protection is a little danger, the high current is looking for a ground and the engine block is a good source of it, most of the spark plug tester are safe to use.
Not to mention, unless I am mistaken, it can do damage to the ignition system having juice going to the unattached plug wires. I’ve always disabled power to the plug wires and fuel pump, if the pump runs of power. Either way you don’t want fuel or spark live during a compression test.
@@boatus I was wondering how many comments I'd read through before finding the "you're doing it wrong" trolls. If it wasn't for UA-cam videos, I can't help but wonder what these guys would be doing, and who they'd be doing it to. This was a great video, and while there are always more than one way to skin a cat, you did nothing wrong....
@@atomicslam1589 Thanks, Atomic. We are always happy for the additional input, which is usually very helpful, because, as you very rightly point out, there are often many acceptable ways to do things--and we do learn some great tips from our viewers and readers. But, yes, we do sometimes wonder why folks who clearly already know so much are watching our how-to videos. 🤷♀️
please let me know your compressiin tester. that is longgerat plug hole than others. it is useful.
Thanks for your question, 김진수. Unfortunately we don't have this information available.
2001 Evinrude 4stroke, 3 cyl. Had very weak telltale and oil temp alarm going off. Replaced oil temp sensor and new water pump. Telltale stream is good, oil overheat alarm still goes off but take a good 15 min. However, new and crazy problem is water now flowing into all 3 carbs??? How do determine cause?
Not good at all, Water Monkey, and not something we feel comfortable tackling as a DIY. We recommend finding a good mechanic pronto. Good luck, and let us know how it turns out.
How did you warm up the engine as you are indoors and don’t have water flow through it?
Great question, Brian. We were shooting in a large garage, and the doors were open. We used a hose and muffs to warm it up ahead of time.
I just tested my 1991 Evinrude "BEFORE" watching this video. My cylinders are all with 10% of one another, but...I did not remove all the plugs at once and the motor was cold. Should I re-check using your method? Thank You
Thanks for the question, Steve. As we mentioned in the video, the compression should be checked with the engine warm. This gives the pistons a chance to expand in the bores and will give a more accurate reading.
Always check the compression with the plugs removed, this allows the engine to spin over easily, places far less strain on the starter motor, and perhaps most importantly, ensures that the engine will not start unexpectedly.
I’m glad to hear that the readings are all within 10% of each other, and although I doubt that there is anything out of whack with your motor, it would probably be best to use the method we described in the video.
Hello and thank you for this video. I am in the market to buy a used outboard 85 HP Mercury motor for my fishing boat and it has not been started in over 10 years. If the motor can't be warmed up because it won't start how would you do a compression check? Thanks in advance.
Hi Omar. For a compression test to mean anything, the motor needs to be warmed up first. An outboard that hasn't started in 10 years is likely to need a number - a large number - of fixes before it can be started. The litany of items to replace is too long to address here, but we wouldn't recommend tackling this alone; having a professional look at the motor is in order for sure. Good luck!
@@boatus Thank you for your advice. Appreciate it very much! Sincerely.
@@OmarGonzalez-uj3ot You are quite welcome!
Hi. I have an 05 250. Where would I find that fuse for the fuel pump ?
Hi Jess and thanks for your question. Unfortunately we're not able to answer questions like these as we're not familiar with every engine out there. We recommend taking a look at the owner's manual, available through Yamaha. Just plug in the info from your engine here: yamahaoutboards.com/owner-center/owners-manuals. I'm not sure if this is the correct manual, but it may give you a place to start: www.manualslib.com/manual/559932/Yamaha-F250.html?page=78. Alternatively, reach out to Yamaha's customer service. An online search shows some videos and articles as well. Good luck!
Our compression test was good, however it really seems that after our engine warms up we are dropping a cylinder, the power will definitely lower and will try to surge periodically. Is this possible with good readings?
Thanks for your question, Shannon. Without seeing the engine in person, I can only offer general advice here. Engine compression should only be checked once the engine is warmed up to normal operating temperatures. This is because hot components will expand and have a bearing on the readings taken. A cold engine will give readings higher than hot engine. Assuming that the compression checks are normal, I would suspect something else, which, from your brief description, leads me to believe that this is most likely a fuel issue. My reasoning is that compressions do not change from moment to moment and cause surging. If your engine has fuel injection, it may well be that one of the injectors is partially blocked and requires service or replacement. Or it could be something as simple as a worn-out fuel filter that needs replacing.
I would thoroughly check all the fuel system components: hoses, filters, connections, and injectors or carburetors. If you are unable to do this work yourself, I would seek the services of a qualified technician. Hope this helps!
do you need water running through the engine.....My manual says, don't crank without water. Should the starter be disconnected ? More I utubes I watch, the more confused I get.
Thanks for the great question, Livio. You do need a water source any time the engine will run, so many people say to make sure it has a sufficient water supply "before you crank it over," which is correct. However, since you remove the spark plugs for this procedure (performing a compression test), there's no chance of the engine firing. Thus no heat is created, and no cooling water is required. The starter, you don't need to worry about. Hope this helps clarify things.
@@boatus sure does....just heli coiled a bolt on the cylinder head...all torqued to 20lbs....cleaned and lubricated cylinders....now will compression test....throttle and choke wide open....fingers crossed
Compression plus 120 on all....this johnson 100ESL may still have a few good years on her....thanks again
Tnx for the informative video ,I have a question plz, whats the normal pressure for yamaha 85hp mix oil and fuel engine and is there a difference in the air pressure gage if is stander engine or 50 fixed or 25 fixed ?👋
Thanks for the question, Sam. If I understand you correctly, you are wondering what is the compression pressure that you should see on the gauge when you conduct a compression check. The pressure should be somewhere around the 125 psi mark but may be slightly more or less. What is more important is the comparison between the cylinders. Check each in turn and note the readings which should show a variation of no more than about 10 psi between cylinders. If one is significantly lower, further investigation will be required as this could be indicative of a stuck or worn valve, piston and bore wear, or some other issue.
@@boatus thats what I meant ,thank u 🙌👋
I have 90 hp year 1986 yamaha and got following: 1# 7,5 barg, 2# 8,5 barg, 3# 9,8 barg. Quite different. What is correct value? Can I use the motor?
I have a 9.9hp mercury 4 stroke. What should the compression be around? I am repairing it currently because the crankshaft was bad.
Thanks for the question, Jared. The actual compression number is dependent on several factors: the age of the engine, the type, whether the valves and valve guides are in good condition, and so on. Check the compression when the engine is hot; a cold engine will give false high readings. I would expect the numbers to be in excess of 100 psi with each of the cylinders within 10% of each other.
Hi sir. Good day. Can i ask about our yamaha 115 four stroke. If i will give rpm. Engine is good. But if iengaged the gear. There is no speed.. pls help
But is every single outboard boat motor the same compression? They’re all 200? I found it confusing.
Hi Jayden. Thanks for the question. It's not about the numbers themselves; the critical part is ensuring that the difference among all the cylinders is within 10%. Hope this helps.
@@boatus ok, thank you. So does it matter that the cylinders **should** be 200, but they're say, 50, and all are within 10% of 50. That would be fine?
Thanks for the follow-up, Jayden. In our experience, most manufacturers won't cite an "official" compression number for their outboards. And you can't put any across-the-board number on it because all engines are designed differently. Our guess is that if you're getting only 50 psi readings, even if they are within 10% of each other, the engine isn't going to run. (If it does, the issue may be with your tester.) Unfortunately, I'm not sure we can be of further assistance without being on site, and your best bet is to consult manufacturer recommendations and/or a trusted mechanic. If you are having a specific issue, you might consider sending your question along with any pertinent info (and photos if applicable) about the specific engine to magazine@boatus.com and we can forward it to our technical editor for possible answer in a future issue of BoatUS Magazine.
@@boatus thanks very much! I don't have an issue now, but just learning about all the various things, and this was a confusing detail that seems to be overlooked. Maybe because it's not very relevant! But I really appreciate your responses.
You are quite welcome, Jayden. Thanks for asking!
When you’re turning the engine over for the compression check do you have to have the water ears over the inlet
Thanks for the question, Jordan. Cooling water is only required while the engine is actually running. The engine is not started when conducting a compression test so, no, you do not need the muffs on the engine. Also, a common mistake when conducting a compression check is not removing all the spark plugs. Removing the plugs does two things: 1. It ensures that the engine cannot be started, and 2. there will be no compression allowing the motor to spin over on the starter easily.
Its good to have water muffs on anytime you turn the engine over so you don't prematurely wear out the impeller.
Do you need to disable the ignition circuit when performing a compression test?
Good question, Gary. You are going to need to use the starter to perform the compression check. As you will have removed all the sparkplugs and disconnected the HT leads to the plugs, the engine can't start.
@@boatus On that motor, if you had used a remote starter switch (www.google.com/search?q=remote+starter+switch&oq=rfemote+starter&aqs=chrome.2.69i57j0l5.8468j0j7&sourceid=chrome&ie=UTF-8) between the battery positive connection at the starter solenoid and the brown wire next to it on the same solenoid, you would not have needed to remove the 15 amp fuse for the fuel system or worried about the ignition firing as long as the key was off and or the emergency stop lanyard was disconnected. At that point, all you would be doing is cranking the pistons, crank and such with no other motor functions. I'm glad to see you showed the technician watching the compression reading as they were taken as that is an often forgotten important component to taking a proper compression reading. Paul Murphy, Yamaha Master Tech.
Thanks, Paul!
I was always under the impression you should disable the ignition system so you don’t damage it if the plugs are disconnected and not grounded. You really only want power going to your starter.
Does cranking over the outboard damage the impeller?
HI Dan. Thanks for the question. For a compression test, you literally only need to crank the engine over one or two time and this is insufficient time to damage the water pump impeller. So go ahead and all will be well if you follow the instructions in the video.
Great stuff
Thanks for watching, James!
At 3:17 you say this piece. How do you know what size is needed to thread into the spark plug? Is it the info of the spark plug?
Thanks for the question, Dave. The owner's manual will have the exact specifications for the spark plugs used in your outboard.
Is it worthwhile to do a compression check on a lightly used 2017 outboard since it is about 2 yrs old.
Thanks for the question! In your case, it's probably not necessary. A compression check is simply one check that engine surveyors and interested owners can do on their engines. A compression check will give an indication of “blow by” of the rings and valves. This is unlikely to occur on an a nearly new engine and I would say that it is unnecessary, unless there is some other fault with the engine such as rough running or excessive oil use.
A compression check can be useful at times but a more useful check would be to get the engine to a local authorized service center that services your make of engine and get them to plug the engine’s ECM into the diagnostic computer. This will show any fault codes and the technician will be able to tell a lot about the health of the engine from this simple check, certainly far more than doing a compression check in isolation.
Ok
Question, I was told by a mechanic that it was bad for the coils to turn the motor over without grounding out the plug wires first, any truth to this?
Your mechanic is correct, Bill. The spark plug high tension leads should all be grounded using a spark checker. Without being grounded, power pack/ECM damage could occur.
I have a 140 Johnson evinriud and I dont have spark can you help?
Thanks for the question, Joseph. This could be so many things: Is the battery flat, are the high tension leads in good shape, is the ECM (engine control module) faulty? There are so many possibilities that it is impossible to give an answer without seeing the engine in person. The best thing I can suggest is that you entrust your engine into the hands of certified outboard mechanic who has the tools to diagnose and correct this problem. You do not say what year your engine is, but the newer engines can be connected to a computer and the mechanic can then download the fault codes, which will go a long way in finding out what the problem is.
Hello I was wondering two things first,
Hi Tom. Happy to answer any questions you have, but they seem to have gotten cut off. Feel free to edit the original or reply if you still want to ask them.
siiiii genial ya que mi motor es un 90 suzuki de pronto ahdecer lo mismo y al conprar un uasado tambien ahde dar la nisma lectura de ub dies por siento gracias
Glad we could help, Dsm. Thanks for watching!
What size adapter did you use? mY COMPRESSION KIT didnt have an adapter to reach thread into plug port
Thanks for the question, Cheryl. You should not need an adapter. As you will see, there is a rubber hose, usually about a foot long, in your kit that has a press fitting one end that goes into the gauge and a screw that goes into the plug hole. Before connecting the hose to the gauge, you should be able to attach the threaded end to into the plug hole by twisting the hose. The hose only needs to be hand tight.
Before conducting a compression test, make sure to remove all the plugs from the engine. This prevents any inadvertent starting and makes it easier for the starter to crank the engine over.
Hey Lenny, where can I purchase a compression tester for my outboard?
Hello, thanks for your question! There is no specific compression tester for outboard motors. You can find suitable compression testers at places like NAPA or Autozone. Since it’s a tool that you need infrequently, you may find that you can rent one from either of these outlets.
I got my most recent compression gauges from Amazon for about $20 with a carrying case and an assortment of adapters and fittings a year or 2 ago and I've used the crap out of them. That's where I'd look.
what is the thread size and pitch for these plugs?
Thanks for the question. The size of the threads varies depending on the make, size, and age of the motor. Older motors used either a 21mm or 22mm thread and required a 13/16 or 3/4 inch socket to remove them respectively. However, most modern engines us a 16 mm plug and require a 5/8 deep-well plug socket to remove them.
Correct.
Thanks for watching, red!
What should a25 horse mercery 4 stroke have for compression
Remember what the tech told us between 0:30 and 1:05 in the video. The key thing to look for isn't one specific number or another, but that all of the cylinders are within 10-percent of one another. Different gauges can vary a bit and elevation is also a factor, which is one of the reasons why looking for the different cylinders to match up is what you really want to look for.
What causes no compression on one side of engine? V6 OMC 3.0. Please help
You shouldnt have a 0 reading on one whole bank of the engine, check you threaded the tester correctly otherwise the only thing I can think of is if it's a 4 stroke you have valve blowby but I have never heard of that happening to a whole bank
Thanks for the question. If you have no compression it can only be down to a few things. Assuming that you have no compression at all on one side of the engine, I would suggest that you have holes in the pistons or the piston rings are no longer doing their job and have totally failed, often due to the engine severely overheating at some time. Another possibility is that the cylinder head gasket has failed. These engines were last made in 2000 and although I don't have much knowledge of these engines in particular I would imagine that it should be possible to buy spare parts. However, you may want to get a qualified outboard technician to give the engine the “once over” before you go spending a lot of money on it, as the cost of repairs may well be far in excess of what the engine is worth.
@@yaboy6157 Thanks for your response!
You stumped him a few times there..
Correct
Good
Thanks for watching!
U not gonna show us that lower one because that one was off right lol it's always the low one
Nah, Brett. It was a new engine. No need to show it for each one.
Why doesn’t boat us get someone that actually knows what their talking about
Hi Justin. Can you be more specific? Sean is a Yamaha Master Technician.
@@boatus I’m sorry was in a bad mood that day and should’ve kept to the if I don’t have anything good to say than should’ve kept my mouth shut., thanks for the video non the less BUT the nitpicks I had:
Said remove all spark plugs so engine doesn’t fire and cylinder gets more air. Shouldn’t fire because ignition system should be properly taken care of by either grounding spark plugs or cranking with safety lanyard disconnected or risk damaging ignition circuit which was never mentioned. Main reason to pull spark plugs is to make it easier on starter to turn over engine due to only having resistance on cylinder being tested. Adjacent cylinders have no influence on air of cylinder being tested but throttle body position does on a 4 stroke so it’s important to open and hold throttle body to its most open position while cranking for most accurate readings.
Fuel in cylinders will not wash out readings as it is vaporized into a gas by the time it reaches the cylinder anyways. How do you think ouboards without a fuel pump(ie carburetion) are tested. Which many people coming for a compression testing video will be inquiring about.
“Certification” credentials are nothing but check boxes for appearance and by no means signify expert subject matter
@@justinkemeter Thanks, Justin. We all have bad days. Appreciate your response. Thanks for your clarification.
Can anyone out there tell me WHY you need a boat? One reason? Anyone? Your hobby of polluting our freshwater supplies is not more important than my grandchildrens future! Private ownership of boats should be banned.
Bernie Sanders 2020!
HAHAHAHAHAHAHA
lzvagias typical mariner. Destroying the environment.
Yes you and all the communists can go to live to Venezuela, cuba ,china, and fix the environment over there
Is Bernie going to be alive in 2020?
While boats do pollute. They are just a small fraction of the reason for pollution. Take a look at how your battery in your phone is made. Or better yet how nuclear power is running your computer. Boats dont have place on a big list of reasons why water and air is getting polluted. Nice try. And for your sake I hope you dont have anything gas powered (lawnmower, car or bus ect). Because in your words, you are also part of the problem.
How about cars they are doing a lot more damage than boats.