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Outboard Lower Unit Help

gcr0003

gcr0003

Well-Known Member
SH Member
Joined
Nov 1, 2018
Messages
8,113
I have a 2006 Yamaha 25 HP 2 Stroke Outboard engine. I saw some oil leaking from the foot one day and when I drained the lower unit I had the milky water in oil come out. I bought a seal kit and changed all the seals. While I had the lower unit off I also changed the water pump impeller. Well after all that I am still getting bypass somewhere. It's no where near as bad as it was (right now just a slight haze to the oil) but I'd like to get it where its not letting any water in at all. Any thoughts? I saw where you could do a low pressure leak down test and try and find some bubbles to indicate where youre getting a leak by. There is also a chance i put one of the gaskets or orings in incorrectly. The lower unit seal kit isn't but $30, I might redo it all again. Any thoughts or experience with something similar? I have been fighting with this thing for months now and I am really wanting to have it fixed before season starts.

Thanks!
 
Pull the lower unit off. Dry it real good. Lay it down on some paper and see if you can see where the oil is coming out. You could try add some air pressure and see if it accelerates it any. I'd rather try to get a positive ID on where it's leaking before I tear something all the way apart again when it could just be something simple. Like the gaskets around the drain plugs... Or?
 
gcr0003 said:
Good thought. I did but I may not have been liberal enough with the application.
Click to expand...
Indian Head gasket cement is what I always used. If the surfaces are a bit rough you may have to apply it thicker.
 
When in the lower unit did you also replace:
-Driveshaft seal under the water pump?
-Did you apply sealer to the metal edge of each seal before pressing everything into the beaing cap?
-when you replaced the impeller, did you get a pump rebuild kit, or just the impeller? Some have a 0-ring seal under the pump that if not sealed it will leak as well

Keep in mind if you replaced some seals, and not them all, the leak was driving down the pressure internally, so a seal that wasnt leaking before may be now that you fixed the main leak...
 
Vtbow said:
When in the lower unit did you also replace:
-Driveshaft seal under the water pump?
-Did you apply sealer to the metal edge of each seal before pressing everything into the beaing cap?
-when you replaced the impeller, did you get a pump rebuild kit, or just the impeller? Some have a 0-ring seal under the pump that if not sealed it will leak as well

Keep in mind if you replaced some seals, and not them all, the leak was driving down the pressure internally, so a seal that wasnt leaking before may be now that you fixed the main leak...
Click to expand...
I initially change the all the top seals including the shaft and impeller oring seals but I didn’t replace the prop shaft seals. I then came back and replaced them after noticing some significant wear on them. I then came back and replaced the gear selector boot because I noticed it had a crack in it too. At this point I have replaced every seal in the lower unit. I drained the lower unit and applied 10 psi with a small hand pump from harbor freight. I read where it should hold 30 seconds per some Yamaha manual or spec but I held it for almost 20 minutes and it only dropped about a half a psi. After talking to some other fellas I think it may just be residual water left in the tank that is making the oil ever so slightly cloudy. I was also using cheaper oil during trouble shooting, which I was told is sometimes naturally cloudy. I will say that it went from pure milk coming out of the unit to just barely cloudy oil. I’m going to run it a few more time and see if it gets worse or stays about the same. 480B43F8-242E-42B6-A381-106ECC476DF7.png136FF088-C1F7-42A4-A7DA-2DEB10CD0344.png
 
bj139 said:
Are you running it only in fresh water?
Click to expand...
I am now, which makes me worry less about corrosion of the internal gears. I use to live just north of the Mobile bay and the Gulf of Mexico and most of the place we ran were higher salinity than your typical fresh water rivers. I’m up in mainland Alabama now and only running fresh water lakes.
 
I think you got it. Check it after running a few times. If you leave the top plug in and remove the bottom plug you should be able to get a bit out to determine the condition without draining it.
 
gcr0003 said:
I initially change the all the top seals including the shaft and impeller oring seals but I didn’t replace the prop shaft seals. I then came back and replaced them after noticing some significant wear on them. I then came back and replaced the gear selector boot because I noticed it had a crack in it too. At this point I have replaced every seal in the lower unit. I drained the lower unit and applied 10 psi with a small hand pump from harbor freight. I read where it should hold 30 seconds per some Yamaha manual or spec but I held it for almost 20 minutes and it only dropped about a half a psi. After talking to some other fellas I think it may just be residual water left in the tank that is making the oil ever so slightly cloudy. I was also using cheaper oil during trouble shooting, which I was told is sometimes naturally cloudy. I will say that it went from pure milk coming out of the unit to just barely cloudy oil. I’m going to run it a few more time and see if it gets worse or stays about the same. View attachment 33443View attachment 33444
Click to expand...
Sounds like you're looking good to me. Run it and check after a few outings. Change the oil at the end of the season again.
 
Vtbow said:
Sounds like you're looking good to me. Run it and check after a few outings. Change the oil at the end of the season again.
Click to expand...
Yea that’s the plan. When I change it then I’m going to use the remainder of this quart of Walmart gear lube to flush it a couple of times then I’m going back to official Yamaha gear lube. Thanks for the suggestions and reply’s fellas.
 
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