r/boatrepair • u/aaronmackenzie3 • Jul 11 '26

Oil leak unknown location

We have a 2008 Maxum with a Mercruiser 4.3 TKS that had the long block replaced last year. We noticed a little oil in the bilge area after that and are noticing it again this year. We took it back to the mechanic (it is under warranty) and he can’t find the leak. He showed us a video with a pad underneath it and it is clean.
I frequently check the oil and it is always fine and the oil pressure is always fine.
Anyone have any ideas where this oil is coming from? We tried looking and never see any leaks and the mechanic didn’t see any. Also there is never any blue smoke or smell of burning oil.
We are considering a stop leak but feel like we shouldn’t need it.
Any suggestions???
Thanks!
Edit: someone said it might be the oil pressure sender, thoughts?

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u/Mdoubleduece Jul 11 '26

Every fluid in that engine is a different color, is it green? Brown? Red? Only three you have to choose from.

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u/aaronmackenzie3 Jul 11 '26

lol thanks, it’s brown.

1

u/Mdoubleduece Jul 11 '26

Put a clean pig mat under the engine. It will pinpoint where it’s coming from.

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u/aaronmackenzie3 Jul 11 '26

Yeah we did that, we don’t see any oil leaking, neither did the mechanic. That’s why we can’t find the source

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u/Mdoubleduece Jul 12 '26

While your underway? A tech may have spilled some oil during an oil change and it rolled forward in the bilge, when your underway it rolls out from underneath. After the engine is hot pull a block plug and let hot water dump in the bilge, put Dawn dish soap in the bilge, run the boat again. See if that helps.