Mercruiser 3.0L 140hp Alpha 1 Black Fluid in Bilge

[Jacalore]

1985 Mercruiser 140hp with Alpha 1 Sterndrive
I've kept the bilge clean between outings. It picks up some seawater during the day, but nothing serious, maybe a cup or two. I've only had it out 2x this year and both times there was a black fluid in the bilge. There's no oil anywhere on the engine, and the fluid smells like a petroleum product, but not quite engine oil. Now, I did coat the engine with WD-40 winterizing last year, but feel that would have evaporated by now? And this year I sprayed down the throttle linkage, but again don't think it would foul the water black. So, I'm at a loss... Steers okay, and sterndrive up/down is okay... can't get to the boat for a few days, trying to get a lead where to start. Any ideas? Thanks.

 

[Fishermark]

Trim fluid would be my guess. Check the level. Many of them use motor oil as the fluid.

 

[DaveG55]

Only 3 things in that area have oil. The engine, the outdrive and the trim system. Any of the three could give what you describe. Check fluid levels in them each, see whats low. Also, check each for water intrusion, the engine and outdrive will have milky shake looking oil (unless the water has settled out) I don't know about the trim oil, never really heard of it getting water in it.

 

[Jacalore]

I wonder if it's fuel? Seem to be using more fuel than I suspected... there is a whiff of fuel when cover comes off. But then again, the bilge water is black... but I was on a cedar water river. Just thinking out loud here...

 

[DaveG55]

You can speculate all day but you won't know until you start checking stuff. Start by draining the bilge into a clear container to see what seperates out.

 

[Jacalore]

Yep, hopefully I can get to the boat in the next day or two and start eliminating possibilities.

 

[Jacalore]

Had a look around today... found two areas possible fuel leaks. One at the lower gasket on mechanical fuel pump. If I press on the lip of the rubber gasket that protrudes from the body, I can see fuel seeping or wetting the black rubber, making it shiny. The other is underneath the fuel inlet to the carb, (that multi-connection setup) definite fuel there. I tightened it a bit and I'll check again after I get chance to run it. No way I can see to tighten pump tho... the top comes off and there are screws holding the body together but not the lower gasket. This is a new fuel pump last year so I'm wondering - maybe it's normally wet?

 

[Fishermark]

This is a new fuel pump last year so I'm wondering - maybe it's normally wet?

Definitely not normal. You need to fix that as soon as possible. Fuel leaks in an I/O are dangerous.

 

[airshot]

Does the bilge water have an oily sheen to it when pumped out? The 3.0 engines have a reputation for leaking main seals, my 1983 does, not a great amount but it does do some dripping into the bilge. I keep some oil mats under the engine to soak up the oil so it does not get pumped out to sea thru the bilge pump. If the DNR or coast guard sees an oil sheen from your bilge pump discharge it can be expensive to pay the fine, besides none of us want oil in our water system. Good luck in your search.

 

[Jacalore]

Ran engine on muffs, found/fixed fuel leak. Guess I'll know for sure after next outing. Starter hung up a couple times before engine started. Is that how they fail?