How To Replace Mercury Outboard Water Pump Impeller
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- Опубліковано 8 лют 2025
- How to service and replace your water pump impeller on a mercury outboard. 75hp, 90hp, 115hp, 125hp.
Larger Optimax outboards run the same water pump, as do Mercriuser alpha sterndrives.
I'm going to comment here so that another "home mechanic" researching this topic doesn't have to go through the pain that I did. First of all, thanks for making this video. I watched several videos before trying my impeller change for the first time. So long story short, nowhere in the the service manual or owner's manual does it say to drain the engine oil before dropping the lower unit. To my surprise, I had a flood of engine oil pouring out when I removed the shaft and dropped the gear box. I tried to research the problem on line and found a few people who had the same problem, but what they were being told was they had a costly engine oil leak and would need major repairs. This just didn't sound right to me, because I could see a hole at the top of the opening where the drive shaft stops, so I started to do more research. I won't go into detail, but the bottom line is that at least on my 2013 115EFI Four Stroke, you need to drain the engine oil before removing the gear case. I confirmed this with three different Mercury certified mechanics and called Mercury customer service.
Wow! AMAZING video with all the info I really needed. Well done mate, well done. Saved me so much time and mistakes I would have made with just my book.
What a great tutorial. I've watched several on here and this one is by far the best presentation .. I like the fact that you didn't get overly technical, but kept it easy for the everyday "shade tree mechanic" to understand.
I will be changing the impeller on my 75hp Merc in about 2 weeks and will have my laptop on the workbench for reference with this video cued up!!
Thanks again!
Great video, thank you very much even all these years later. A couple notes - one, you can't really see the orientation of the face seal you put on top of the waterpump housing, I had to look that up elsewhere. My kit came with the seal and an install tool. The seal goes with the wide thin flange down against the top of the housing - the tool keeps you from pushing it inside and helps seat it nicely. Two - the bottom gasket on my kit was a thin metal one, and according to the papers that came with it replaces the large fabric gasket. Must be a new version or something. Finally, the rubber seal that you see at the end of your video on top of the housing water jacket did not drop out when I removed my lower unit. I ended up just greasing it a little in place, since the kit did not come with a replacement and I didn't want to risk trashing it. Thanks again! I don't know what people would do without tutorials like this one on youtube.
Thank you for this video. I contacted several local mechanics to get this done but all said it would be a 3-4 week turnaround. I picked up the parts myself and it only took me about an hour and saved me all the labor cost. Awesome!
Looks like I can remove the gear box without taking the boat out of the water. Normally, I would be afraid of doing any work over water.
Dad (90 yrs old) wanted fishing trip with his two sons.I fly to SLC UT. Brother picked me up at airport, drove to dads, picked up him and his boat and headed to Flaming George. Got boat down to dock and thats when things started to unravel.
1. Batt dead - jump cost us $10.... then learned it's been one year since boat was in the water !!
2. Five minutes into lap close to marina to make sure engine can burn older gas mixed with stabilizer plus five gal new - a warning alarm came on - ZERO water pressure on gauge - no cooling water coming out of port. Marina tech stated impeller problem (dad has never changed it in 9 years ownership). One week to get part. at $145 - Two weeks to work it into schedule at $125 labor. Ok - back to brothers house - trip over.
On a whim thought about youtube... Watched your video.. then found impeller kit online on Amazon - $38 + $4 overnight delivery!
Watched video again - I can do this! Had it apart in 20 minutes... 5 being used finding a 15mm socket in brothers very limited tool assortment.
Thanks so much for your help saving a father/sons 4 day fishing trip!!
Thanks for the feedback Dale, Glad I could help! :)
That trip was setup for disaster from the jump. Hope you guys had fun anyway
Awesome video. Thanks for work putting it together!
Man I've seen quiet a few videos and tutorials but none of them made sense to me. You had the best tutorial and very easy to understand. Cheers bro
Omg... An internet mechanic that doesnt wear gloves... I salute you sir!! Youre a real mechanic.
Great video. Some years ago I had an old 1971 2-Stroke 7 1/2 HP Mercury Outboard. I changed the water pump impeller several times. Kept going out. I then changed the whole housing everything thinking something was wrong because it kept eating impellers. I think it lasted longer after replacing all of it. Boat we have now has two Mercury 4-Strokes and have never had water pump go out. Replace the impellers every three years.
Thank you for posting this video! Going to try my hand at helping a mate get a 115 pumping water again. You saved me quite a bit of time by describing the impeller renewal process brilliantly.
Thanks for taking the time to make your video! I own a 1987 Mercury Mariner 75HP and have hesitated to replace the water pump myself. Thanks to you I will be doing it in a few weeks. You took the mystery out if it and made it clear and simple to understand. Keep on making videos! Thank you.
Very good thanks! I watched this and it gave me the confidence to clear the sand and shells out of my impeller rather than taking it into the shop. Used a water blaster through the top hole of impeller rather than disassembling it and a few 5mm x 5mm shells popped out! Impeller now pumping water as usual. Many thanks.
I watched a lot of videos and no body demonstrate the way u have done it regarding in impeller replacement its a bit confusing u made it simple thanks
Ty dude they wanted 800 to change I did for 75 but I was looking on top of motor were water comes out your video is gonna make make owners of companies mad cuz it was easy once shown Ty again
Hi Geoff, i just subscribed to your channel. I have to change mine on my mercury 90 HP outboard motor this week. This was the best detailed video i found so far. Thanks for helping us boaters out. Now i know how to handle. I am use to working on my LT1 trans am.
Great video - very helpful to understand the relative simplicity of this job.
Only one nit to pick (sorry!): You commented a couple of times on "keyway", but were referring to the key itself. The keyway is only the slot in which the key installs.
Other than that, we get what you meant. Thanks for posting this!
Really good explanation and excellent tip about the direction of the drive shaft so the key can be easily aligned with the impeller. Thank you
You are a champion! Short, consise, and to the point. One thing I would add is the ft-lbs or whatever torque measurement you use for the bolts on the pumps housing. Some guys are sticklers about that sort of thing :)
Great video, thank for the attention to detail!! Most others don’t even bother with the pertinent info!! Thank you
Great video. I just changed the water pump impeller on my Optimax 115. The only difference was that mine is a long shaft and the gear shift selector rod is longer. Great advice to put the motor in forward gear as it makes it easier on the install.
Thank you for this! I have a 1998 Force 90hp and could not find a video. This engine lower unit is identical to mine. Thank you so much! Worked like a charm.
Fantastic step by step instruction, easy to follow with no missing information. Thank you!
This video helped me out a lot today! I replaced the water pump and changed my lower gear oil in about an hour. This video was spot on. I have a 1996 force 120 by Mercury. Saved me lots of money. Thanks a lot!
This may be a dumb question, but did you drain the lower gear oil first, then work on the water pump, then refill after reinstalling? I'm about to do the same on a 96 90hp force.
@@bbreede1 I did the water pump first, then changed the lower gear oil once everything was back together. However, it shouldn't matter how you do it. It was a pretty easy job honestly. Good luck.
You saved me a lot of money by making this video. Thank you for going to the trouble to do it.
Well done!, I'll be doing that to my 125 this week. Kudos for going the extra mile and greasing everything for the next time!
Nice video thanks someone finally shows disassembly and reassembly with some advice to this video was very helpful
Thanks for the comment
Great video. You covered all the points in a clear manner and your video was concise and very useful. Thank You!
one of the best IF not the best vid's on changing a water pump ... Great Vid Mate from the US!!
Good show. This is one of more complete and informative ones that I have seen.
@OutboardAdvice
I am in the process of doing a Mercury 50 and on my motor there is a nut that you have to loosen on the shift linkage. It is on the front side of the lower unit and is accessible prior to loosening the other 5 bolts holding it in place. I had the same problem as another person here where it only dropped down about and inch or too unit I disconnected the shift linkage. Hope this helps someone else with a similar motor in the future. Great video by the way.
I agree. One of the best videos on this subject. Makes me want to get out there and do my Merc. 9.8 which has been sitting for quite a while. Wasn't really using it anyway but I'll find a purpose.
Excellent explanation of the procedure and tips to make the installation go smoothly.
This video tutorial is brilliant !
Clear, educational, useful... Got me on my way.
Thanks mate!
Awesome- I have a 2011 115HP Mercury and this video is extremely helpful- thanks for posting.
This is just a well made and informative video. I just took apart my 2016 CT 90 Mercs water pumps after 340 hours. They are one year old in August but this is Vermont so they do have from November to March off. When I was replacing the cowling after shift maintenance, I saw a maintenance schedule printed on the inside cover that said to replace the water pump impeller every 300 hours. This had me concerned but the boat was put in the water without changing the impellers (2 motors). I have over heating problems and had to pull the boat. The over heating happened only in reverse where the old impellers were not strong enough to overcome the vacuum created by the water rushing past the intake ports. I am now more concerned because your video showed putting silicone on an area to prevent exhaust gases from entering the water intake (10:20 into the video). I will look into this and report back.
i put a piece of wire into the water hole it worked there was a bug in there. thanks you saved me a bunch of headaches. and repairs.
Great video...plan to replace the water pump on my '72 Merc 115hp. The one I burned out by forgetting to turn the hose on last weekend when I was driveway starting it. D'OH!
Good video - I always put the motor in forward gear before dropping the lower unit and make sure the lower unit is fully in forward when reinstalling unit. It is possible for the shifting gear to be moved to neutral or reverse. If you reinstall the lower unit with the lower unit in a different location that the powerhead, the unit can start in gear.
I was looking for information on this. He doesn't mention it in the video. It is necessary to be in forward though?
I can't thank you enough! This video saved our vacation and countless dollars in repairs.
Well done, Geoff, awesome demonstration, many thanks
This is a GREAT video! Not just for boats but overall this lays to shame alot of other instructional videos. Well thought out. Good tips. Showing everything being done. NICE WORK!!1
Finally someone that shows it how it is. Awesome video bud. Thanks.
When applying silicon should I let it get tacky before putting back together or should I do it wet/tacky? Then how long should I let it dry before running it? Thanks, the video was the bomb for me, saved me mucho dollero!!
Well done, great video, very professional and easy to follow.
Excellent how to video . I hope mine goes just as easy as yours . Really like the step by step instructions. Thank ya for the little tid bits of info to . Didn't know it was that easy. Now I'm all jacked up to do mine . Thanks again for a awesome video. 😊
Great video. You covered everything that needs to be and how to do it. Very complete and I’m glad I found this one compared to some of the other ones. . Thx again..
Excellent video! My force 120HP is exactly the aame as the featured Merc. Outstanding detail.
Thank you for posting. With your help I just replaced the impeller on my Mercury 90hp 2 stroke.
Terrific instructor. U must be a professional marine mechanic.
Great video. I’ll be doing mine this weekend. I just got a 2001 125 Mercury.
Great vid, well done and nicely explained. I recently learned that Honda 40hp OB flywheel/shaft turns counter clockwise where upon we also discovered that someone incorrectly installed the impeller meaning the impeller splines "scooped" not "swept" the water. Not sure if you know what I mean. I plan to replace the impeller on my 2004 125hp merc shortly so thanks for this video.
Cheers
Best video i've seen on changing a water pump. very useful/competent
Awesome Video. Not as hard as I thought it might be. Thanks.
Thanks for this tutorial. I have used this many times.
@OutboardAdvice thnx mate for that information, you are the only one who could give me results on the problem.your a wizard
Great video! My husband really needed this.
@petieohalloran The pressure relief valve is a valve that 'pops' off it seat when the engine rpm is increased which increases the water pressure. It bypasses the thermostats etc and make the motor run cool at higher rpm. It has a rubber grommet that gets squeezed in by salt build up and pinches on the plastic valve. There is also a diaphragm that needs servicing/replacing if it is stretched, perrishing or gets a hole in it.
Well made video. Good job, thank you so kindly and keep up the great attitude!
Cheers
Nice video clip. It saved me money taking it in to the shop.
Thanks for making this video! It helped me change my water pump for the first time. Great job!
Thanks for your information. I have seen factory produced videos that were no this good.
Great advising Video and great performance. Thanks from Greece.
good vid with a good camera positions, the rv silicone to prevent the exhast gasses is one of my problems. thx for the info
Thanks. This video is well done and should make my impeller change much easier with no guess work. Great video!
we need more people like you in this world
This is THE GO TO tutorial!!!!
@tasmania105 I had the same problem. the drive system is spring loaded and it went into forward drive when you took out the shaft because the gears are spring loaded. I haven't had time to figure it out yet but some how you need to take the lower end off again and try and figure how to put it in nutrel be for putting the shaft back in. It may take two poeple to do that so one person can hold it in nutrel while you put the shaft back up into place
Thanks for taking the time. Very helpful
Kevin, I did mine today. The bolts are in different areas, but procedure is the same
Simple and to the point, Very good info, thanks
Thanks mate... All outboards are very similar yes. The only real difference is how many bolts (and where they are) that hold the gearbox on. I think from memory your motor will have four bolts, and a nut at the front.
The other difference is the gearshift. The 90 in the video has a splined gearshift. Your motor will need the gearshift disconnecting to remove the gearbox. I think your gearshift disconnects above the gearbox at the front of the motor. Look for a shaft that is threaded.....
BEST video on youtube about impellers. I have a question for you since you know what you are talking about! I have a 2000 mercury 125 that is extremely hard to start. And it will start up after it has been running but if i fish for about 30 minutes, it is hard to start all over again. Is there a trick to starting it that I am not aware of or is this something else? Thanks for your time!
@ober51 Thanks for the feedback!
You will probably find it is exactly the same water pump. If it has the quickfoot gearbox I think. So if you follow the video you should be great! The only thing I have noticed from comments is the gearshift. Before putting the gearbox back onto the motor, rotate the prop shaft and confirm that it is still in neutral and you havent accidentally turned the shift shaft. Good luck!
Great video mate. Before removing it, you dont mention if the gearbox should be in nutral or in gear?
First off, thanks for the video its a big help.
I have a 2006 mercury 115 4 stroke and removed all 5 bolts(left on threaded a couple turns do the housing wont fall off. I cant get get the housing to come loose. Not even enough separation to wedge something between the housing and the drive shaft housing.
I've tried spraying wd-40 around all 4 posts and banging with a rubber hammer. Still won't budge.
Any suggestions for breaking this loose.
Thanks,
ps I copied this to your FB page.
Thank you very much for the video. It was very informative and made changing the impeller a breeze.
very well explained, good video footage and some smart tips. Thanks Geoff
Usually is is caused by corrosion build up around the studs that hold the gearbox on. Or the locating dowels. I have had one that was so tight I had to heat the gearbox so much that the paint needed repairing. LPG is good as it isn't as hot as acetylene. It may not get it hot enough to remove though. You can carefully wedge a very sharp object between the mating surfaces. The best place is at the front, and at the back. I have a razor sharp scraper that tapers thicker.
Awesome job with explaining how to do this job, it almost looks easy.
@radoslavrigas
Hi, yes some kits come with the black tube. Depends what kit you get. When you remove the gearbox the tube can stick onto the water tube. You simply reach up and pull it out then fit it into the water pump.
It is there as a guide for when you install the gearbox to get the water tube to slide into the water pump housing.
Thank you so much for the feedback! I have the seals and I am going to replace them, I'll also check the pressure. You're too kind
Very helpful. I have an older 1974 Mercury 115 6cly outboard. Would there be any difference in parts or assembly?
Thanks for the reply.
Going to tackle this over a 3-4 day time frame. (heat, pb blaster, tap w/rubber mallet.... let sit, repeat) I've been known to break things when I get frustrated, so gonna take my time. I may even come up with my own "spreader" tool using turnbuckles and wood that will fit between the "fins" (I have a 7 1/2 inch gap, so a normal wood wedge is not working). There is absolutely NO gap to get anything in there yet. Give me 1/16 and I'll slam dunk it.
Thanks agn 4 your rply
Very good vid!!
Thank you from Italy.
I'll do on my engine next week.
Really great video. I`m about to change the impeller on my 75HP Optimax. But some people also put some silicon on the seal kit on the impeller house, is that really necessary? I thought the metal seal and paper seal should do the sealing itself.
@jasoncady
Thanks for pointing that out - One piece of advice to anyone with this style of motor. Undo the lock nut first, just enough to nut hold the joining nut. Then undo the joining nut to remove the gearbox. Don't move the locking nut from here. When you install the gearbox, do the joining nut back up then nip up the lock nut. This should keep the shift rod in the same position as before. If you put it back in a different position, the gear shift linkages can be out of adjustment.
Good Onya Geoff……… needed those tips 😊👌👍
@Dualcats2
Similar... You will need to undo the gearshift rod under the carburettors before you can take the gearbox off your motor. It will be a 1/4 inch bolt that you will need a 3/8 inch socket to undo.
FANTASTIC TUTORIAL THANK YOU
This was great. Thanks Geoff.
Did you use the gaskets? The plastic tube is just a guide to guide the water tube into the housing, so thats ok
That kit also does mercruiser alpha 1 water pumps so that is why you had extra bits.
Depending on how deep the grove was in the housing... I very small grove is pretty normal. I would get a housing for next time you do the water pump. It is caused by sand and grit etc getting sucked into the water pump and is very abbrasive....
Its the hose for your speedo. Gets water pressure from the small hole in the front of your gearbox.
Great video. thanks for posting. Just what I need to rebuild the water pump. thanks again!!!!!
Left out a very important bit of info....i.e. How does the gear shifter come apart?
excellent video , very easy to understand , thanks
Oldie but goodie, thanks a lot!
Wow this video was absolutely fantastic. Thank you! I have a 1990 115 HP and I was wondering what may cause water to get in the lower end? Anything I can do on my own to fix this? Someone suggested changing the seals that are behind the prop, is there anything to this? Any advice is greatly appreciated!
awesome video. gives me the confidence to go ahead with this repair.
This video really helped me! 😊👍
Did we miss the part of disconnecting shift linkage First? Not sure how to do that part. Mid 80s 75hp 2 stroke. Please explain shift linkage unhook
Thank you
Thanks for the video . My kit came with two identical gaskets for the plate it was very helpful that you showed one going under the plate. Should the other be left out or go on top? Also I saw silicon being used sparingly but not gasket sealer is gasket sealer necessary?
Also I appreciate you showed the seal going over the shaft and into the housing .I have orings left over but nowhere to put them on the shaft .It is an old Mercury 500 50 horse out board . Thank you for any help, dont want to have to do it all over again