Gunk in lower unit

1989 Johnson 50HP engine, water pump died (so I thought) so I tore the lower unit off for replacement. What I found wasn't what I was expecting. It appears my water pump wasn't bad (replacing anyway), but the output grommet was pinched on installation causing water to bypass going to the engine and just "squirting" around inside the lower unit mixing with exhaust and making this muck. I drained the lower unit oil and it was clear, no "milk" from water intrusion and it was full, so I see no issues there.

Has anyone ever seen this before? Is it what I think it is, in which case I don't have any worries? Under the water pump was clean as a whistle, this muck was isolated to the exhaust housing area directly above the water pump housing.

Have never seen it myself in 50 years of boating & working on OB motors, but as long as you clean up everything up really well (like inside the power leg), then I would not worry about it one bit.

Just put it back together correctly ...

DaleH said:

Have never seen it myself in 50 years of boating & working on OB motors, but as long as you clean up everything up really well (like inside the power leg), then I would not worry about it one bit.

Just put it back together correctly ...

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You can basically eat off of it at this point. Something I learned a long time ago with machines, clean is absolutely critical to longevity.

To add to things a bit. I am replacing the water pump and thermostat, while everything was apart I flushed water from the thermostat through the water pump passage in the exhaust housing. Water ran clear and free, so there doesn't seem to be any gunk in the cooling system. I didn't think there was based on observation, but wanted to double check. This gunk was only in this specific location.

I think I would feel more at ease if I knew what this gunk was, other than my speculation based on observation.

I’d guess as congealed exhaust residue (oil & combustion by-products) ... don’t over-think it ...

Was the motor running good otherwise? Ive seen this happen once on a 15hp Evinrude but all of that gunk in it was due to the motor having a bad powerpack and and not creating a good high speed spark. It basically was running incredibly rich and wasn't able to burn off the fuel mixture so it was coming out somewhat unburnt and mixing with water which created a gray/black sludge.

wmk0002 said:

Was the motor running good otherwise? Ive seen this happen once on a 15hp Evinrude but all of that gunk in it was due to the motor having a bad powerpack and and not creating a good high speed spark. It basically was running incredibly rich and wasn't able to burn off the fuel mixture so it was coming out somewhat unburnt and mixing with water which created a gray/black sludge.

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Motor runs great. Used it all last year and it never missed a beat. I will say this, I run a trotline for crabbing so a typical day consists of idling in the early dark hours, maybe 10-15 minutes running hard once dawn breaks, then 6-7 hours of idling, and finally 25 minutes of WOT to get back in. I know the long duration of idling can be a contributing factor here. Honestly I was seeing a touch of oozing last year and figured it was just the way I was using the engine and didn't worry about it. Now I know what it was from. lol

I've had it happen before. As long as your powerhead didn't overheat due to lack of water, there should be no long term effect. I would make sure the drain hole in the front of the lower unit is clear. That gunk should not have built up like it did if that drain was working properly. Not a problem during normal operation, but it could cause the casting to split over the winter.

Good luck!

All back together and everything is workin great! This motor has never had water squirt out of the tell tail with such force. My mind is at ease knowing this is squared away. Thank you to all that commented!