86 Mercruiser 140 oil leak

G

GLT L22

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Aug 9, 2010
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Just bought first boat....oil/water in Bilge after first time out. Trim pump oil remains full, engine oil level shows a little above full (~1/8" on stick). I cleaned it all up took it out again and traced oil from the top near the air filter/carburetor. Valve cover gasket doesnt appear to be the source. Did previous owner overfill? Would that cause the oil to blow out air intake?
 
Bondo

Bondo

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Re: 86 Mercruiser 140 oil leak

Would that cause the oil to blow out air intake?
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Ayuh,... Welcome Aboard,.... Is the oil, still oil colored,..?? gettin' Milky,..??
 
G

GLT L22

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Re: 86 Mercruiser 140 oil leak

I love to tinker and trouble shoot...so I figured I buy a boat. Engine oil is clean, no water mix. Definate trail of oil coming down from the air filter though. I also have a trail of oil coming down the side of the engine cover from that same area. I plan to first drain a bit of the oil out to bring the oil level down and see if that works. I am just concerned that it can't be that simple.
 
antsmands

antsmands

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Re: 86 Mercruiser 140 oil leak

GLT L22 said:
I love to tinker and trouble shoot...so I figured I buy a boat. Engine oil is clean, no water mix. Definate trail of oil coming down from the air filter though. I also have a trail of oil coming down the side of the engine cover from that same area. I plan to first drain a bit of the oil out to bring the oil level down and see if that works. I am just concerned that it can't be that simple.
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Sounds like a lot of oil is getting into the crankcase vent/rebreath system. Do you know what weight oil is in the boat. Maybe too thin. Is it burning oil? My valve cover had a leak at the gasket where one of the bolt is. A new valve cover gasket and gasket seal fixed the problem.
 
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DayCruiser

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Sep 24, 2004
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Re: 86 Mercruiser 140 oil leak

My 89 does the same thing. I use 10w 30 Mobile one full synthetic. Long as it runs good and its not using much oil. I don't pay it much attention. Just a old boat LOL
 
G

GLT L22

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Re: 86 Mercruiser 140 oil leak

Not sure what weight of oil is in it. Just bought it and haven't changed oil yet. I will just change it out, use the factory rec weight and see if that helps. The engine is not burning it...it has been running great. Oil pressure good, tempt good...I just have an oil spill to clean up in the bilge after every run. The gasket looks like it is holding well. Is the "filter looking thing" on top of the carburetor a true air filter or is it actually called something else? (naive when it comes to boat engines). Is there an air oil seperator that needs cleaning?
 
NHGuy

NHGuy

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Re: 86 Mercruiser 140 oil leak

The air intake thing is a flame arrestor. If you have sticky rings you can get positive crankcase pressure where you would normally have vacuum. Run a can of seafoam in the crankcase for an hour or two before you do the oil change. While the seafoam is in there don't go full throttle or WOT. Maybe 80% maximum. That stuff is awesome. You can also run some through the fuel supply, it cleans up carb & valve surfaces. Although if it already runs correctly it may be a waste of effort. You know the saying, "if it ain't broke"?
 
antsmands

antsmands

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Re: 86 Mercruiser 140 oil leak

NHGuy said:
The air intake thing is a flame arrestor. If you have sticky rings you can get positive crankcase pressure where you would normally have vacuum. Run a can of seafoam in the crankcase for an hour or two before you do the oil change. While the seafoam is in there don't go full throttle or WOT. Maybe 80% maximum. That stuff is awesome. You can also run some through the fuel supply, it cleans up carb & valve surfaces. Although if it already runs correctly it may be a waste of effort. You know the saying, "if it ain't broke"?
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+1 on the seafoam. Also take the flame arrestor off and clean it with brake cleaner. I all metal. No paper filter material. I use straight 30 weight oil in mine and it seems to work well. I do get a small amount of oil in my bilge also but it a 20+ yr old motor. Just keep you eye on it and tighten up stuff if it get higher.
 
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