2002 merc 305 water in oil

Serkit

Cadet
Joined
Apr 27, 2019
Messages
14
Hey,

Have an ongoing problem with my 2002 maxum that has a merc 305 CID v8 open water cooled in it. Last year while getting the boat ready for summer my oil change revealed about a cup of water which poured out first (oil hose which exits from the bilge)followed by milky oil. I had an over heat alarm go off once but the boat ran fine after, at the time I believed the sensor was faulty because it would not go off, had to unplug battery to get it to stop.

I replaced manifolds and risers after hearing these engines are bullet proof and very rarely blow a head gasket. I put about 20 hours on the boat this year, had to rebuild carb because it was flooding very badly and wouldn’t run right. Besides that 0 issues.

Pulled out boat this week and did a spark plug/oil change spark plugs all looked the same, black, not oily, not tan,not white, BLACK. The oil was sludge, milky thick sludge, oil filter was globbed at the top and below it was about 4 ounces of liquid.

compression perfect, exactly the same as the reads from last year in every cylinder.

any ideas? Is it possible I have gas in the oil and not water from the carbs flooding, had a buddy on the boat when it happened and he claimed he tried to start it for a solid 15 minutes so who knows how much worse he flooded it himself.

if not would bad water shutters do this? They looked old but functional when I did the manifolds.

Worse case head gasket....which is probably what this is.
 

alldodge

Supreme Mariner
Joined
Mar 8, 2009
Messages
31,226
The oil was sludge, milky thick sludge,

Gas in oil just thins out the oil, water changes it to milk and sludge. It either has a head or intake manifold leak
 

Serkit

Cadet
Joined
Apr 27, 2019
Messages
14
Higher chance of intake leak? Engine has 200 hours on it. Gunna pull intake in spring and see, just don’t think I want to do a full head gasket job
 

Lou C

Admiral
Joined
Nov 10, 2002
Messages
6,802
Did the oil smell like gas?
Do you have a mayo like coating inside the valve covers? That’s a sure sign of water in the oil.
Possible causes:
rotted out intake under the thermostat, bad intake gaskets, blown head gaskets or cracked head. When you got the overheat alarm how bad was it? If really bad you could have cracks in the exhaust valve seat area of the heads and/or split fire rings on the head gaskets. Doing a cyl head r+r on a Chevy small block is not a bad job at all. They are easy to take apart just clean it spotless before taking it apart and keep all the parts marked and organized.
 

Scott Danforth

Grumpy old guy who plays with boats
Joined
Jul 23, 2011
Messages
33,384
Higher chance of intake leak? Engine has 200 hours on it. Gunna pull intake in spring and see, just don’t think I want to do a full head gasket job

engine is 18 years old and you only have 200 hours on it?

suggest you pull the motor long before spring. moisture and machined surfaces tend to rust.

places for water to enter the oil in order of probability with a SBC :
  • leaking manifold to elbow joint
  • failed flapper from an over-heat and run-on
  • cracked exhaust manifold from lack of winterization
  • cracked block from lack of winterization
  • rusted thru head
  • rusted thru intake
  • cracked cylinder head from an over-heat
  • warped cylinder head from an over-heat
  • leaking intake manifold from an over-heat
  • leaking head gasket from an over-heat
 

jimmbo

Fleet Admiral
Joined
May 24, 2004
Messages
9,270
I agree with and 2nd Scotts advice about not waiting till spring, unless of course, you plan on replacing the crank, cam, and everything else that is made of iron, or an alloy containing it
 
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