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Sludge from lower unit after rebuild

J

JZ54

New member
Good Morning,

I acquired a 1986 Mercury outboard motor from my grandfather who said he ran it for about 10 hours back in the same year and never again. He stored it in his garage for 35 years. I found he had not drained the gear lube and there was a little water in it. I pulled the lower unit and gutted it out to see if there was any rust. There was some but not a ton and I went ahead and cleaned everything, replaced the bearing and raceway, thrust washer, spark plugs, and all the seals. I tightened everything down and filled it up with Quicksilver gear lube which was a blue color. I ran this motor for about 2 hours on the river and then put the motor back in the garage. 2 days later I came out and saw this sludge from the lower unit. Any idea what is going on here?

MotorSludge.jpg
 
First thing I would do is pressure and vacuum test to see if there is a seal leak, Does that goo smell like gear oil? I wonder if your grandfather really pickled the engine with storage seal to keep it from rusting internally during extended storage and now your Merc is trying to get rid of it. Did the engine smoke like crazy?
 
I did do a pressure test before filling it up and it held steady at 12lbs. I didn't go higher than that. As far as storage for the engine, I pulled the sparkplugs and inspected inside but didn't see anything of concern but that was it. Initially it did smoke pretty good and some brown liquid streamed down the engine from the exhaust. Seemed to go away after running it for a while.

I collected the "sludge" and it has turned into to a black liquid form as it sat in the container for a few days.
 
12 psi is plenty, I do them at 5 psi overnight and then 5 inches vacuum overnight. So your good. Take it out again and run it hard and see if the crud goes away.
 
You probably need to fill and flush a few times more to get rid of all that gunk.

You might try flushing with kerosene, letting it drip out over night before refilling.

Jeff
 
I did smell it as asked and it smells like it came from the engine. Just that burnt oil smell but this is a 2 stroke. What throws me for a loop is where is it coming from as it was all in behind the prop. I'm no boat motor expert as this is my first boat but I'm decent with a wrench.

When you say fill and flush, this doesn't have an attached gas tank and I would need to run it to suck up the gas/kerosene into the engine. Is that what your implying?
 
I would guess that this is unburnt oil/gunk in the exhaust, that's what it looks like to me, this is a through hub exhaust, so the gunk will flow out through the hub.
You say your grandfather ran it for ten hours. Breaking it in and the fuel mix 25:1 ?.That's a lot of extra oil. Just my guess.
 
First I really appreciate everyone's input. It's helped a lot.

So you said it looked like unburnt oil/gunk. I decided to pull the spark plugs and check the gaps. They measure .70 mm and are NGK BPR6HS. I looked online for a 1986 Mercury 9.9 and it looks like they say it should be 1.0 mm gap and use NGK BP8HS-10 sparkplugs with that 1.0 mm gap. When I took the old plugs into O'reilly's they gave me what they said was the equivalent spark plug for the old Champion ones I gave them. That will teach me to just trust what they gave me. I think that may be the problem. Looks like they don't stock the BP8HS-10 plugs locally so I'll order them, install, and see if that makes a difference but I am thinking that may have been the problem. Gap too short not burning efficiently.

Thoughts?
 
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