Boat seems to be leaking fuel/oil???

[udm328is]

Latest issue... I take my boat out, I get to wherever I am going or back to the dock and there is a bit of what looks like an oil slick coming from behind my boat. My bilge is clean so I know I am not having issues with my gas tank leaking. I had an issue with my drive leaking gear oil at one point but have since fixed that. Could it be residual? My other thoughts are everything was replaced in the drive and lubricated, could it be any of the lubricants? My final though is could it be my boat is not fully burning the gas and it is coming through the exhaust? If so how do I figure this out and more importantly how do I remedy this issue? As always thanks in advance for any and all help!

 

[Fun Times]

Hi there, For starters, what engine and drive model are you working with?

Do you see it while the engine is on or off or both? While in gear or out? Don't rule out your trim cylinder rams/trim pump fluid. Does the boat sit in the water or on a trailer?

 

[udm328is]

Hi Fun Times, thanks for your reply. It is a 92 Mercruiser 5.0 carb with a Alpha One gen 2 drive. I trailer this boat and don't seem to see anything leaking other than water and once it dries out nothing. I don't think I have ever noticed anything while the motor is running but I will definitely check that when I go out later. Mostly it is when I cut the motor at the dock or pulling up to the island near me. If you have any particular thoughts let me know and I will definitely get back to you after I take her out later to get more specific info.

 

[Scott Danforth]

could be any of the following with your mercruiser:

gear lube leaking out (and water leaking in)
power steering oil cooler leaking out power steering fluid (and leaking water in)
oil cooler (if equipped) leaking out oil (and leaking water in)
trim cylinders leaking oil out (and water leaking in)
head gasket breach leaking out oil (and leaking water in)
bad plug(s) (not firing) with unburnt fuel exiting the exhaust
leaking needle and seat in the carb, dumping excessive fuel with unburnt fuel exiting the exhaust
bad fuel pump diaphragm with extra fuel dumping into carb with unburnt fuel exiting the exhaust

with that stated, start checking all the fluids. you may need to pressure test the drive.

with any petroleum sheen, you need to find it and correct it. the fine is huge for leaving petroleum in the water. it is even bigger if you try to cover it up with dawn dish soap or other dispersants.

 

[bspeth]

Remove the drain plug from the drive and sample some lube to look for water.

 

[udm328is]

I definitely am not looking to cover anything up, I just want to fix it. I am sure it is nothing to do with the drive unless there was residual gear oil lingering from when I had a leak. The upper half is brand new as of the end of last season and all seals have been replaced and the drive was pressure tested. I don't have an oil cooler so at least I know I can rule that out. I don't think I am losing any trim oil but I will take a close look and see if it looks as if water is getting into the oil. There definitely is no water in the motor oil so I am good there, Based on your info. I am leaning more toward unburnt fuel. The only two reasons in my way of thinking and correct me if that is not a good way to think as I am a bit of a novice who has learned almost everything other than changing oil and a battery on here that if it were a fuel issue she would be running rough and that I would smell gas on the water, so I am going to start with giving the trim pump a good look. Thanks as always, I will look this over now and check back in.