Mercruiser 6.2 with coolant in oil

mikedz

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Jun 12, 2013
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So here goes my first post to this forum...

I changed my oil this past weekend and noticed there was some coolant in it. The oil was milky (I had just run the engine up to temp) and there was a little that had separated at the bottom of the pan. It is a 2003 6.2L closed cooled inboard with about 350 hours, and has been running fine. I have not had any issues with overheating since I bought the boat.

I have already checked the coolant, and it was good for temps well below what it saw over the winter so I think the block is OK.

I also ran a compression check. All cylinders were between 160-180psi with no slow leak of pressure, so I think the head gaskets should be fine.

I'm not sure if it is related, but I did see a couple of drops of coolant below the front of the engine the last day of last season. I haven't been able to pinpoint where that was coming from.

I have read about coolant leaking into the block through a seal on the back of the water pump, but have heard that's not possible on the 6.2. Is that correct?

Anybody have any thoughts? My thinking right now is a bad intake manifold gasket.

Thanks in advance.
 

alldodge

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Re: Mercruiser 6.2 with coolant in oil

The leak could be the places you mentioned but I agree the water pump is not possiable. Sounds like it is the intake since the compression test is good, but heat does things to an engine.
 

achris

More fish than mountain goat
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May 19, 2004
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27,468
Re: Mercruiser 6.2 with coolant in oil

Correct on the water pump. A leaking seal there would have coolant in the bilge, not the oil. Do a pressure test on the cooling system, that will find out where the leak is (just listen for the hiss).

Chris.......
 

mikedz

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Re: Mercruiser 6.2 with coolant in oil

I ran the pressure test...and now I'm more confused. I pumped it up to 20psi as the instructions said to, but there was no loss of pressure or hissing to be heard.
 

muc

"Retired" Association of Marine Technicians...
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Jul 7, 2004
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Re: Mercruiser 6.2 with coolant in oil

Did you drain the coolant before doing the pressure test? You should.
Might need to do the test with the engine hot.
Are you sure it’s coolant in the oil and not water?
 

mikedz

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Re: Mercruiser 6.2 with coolant in oil

I ran the pressure test according to the merc manual, which said to remove coolant until it is about an inch below the filler neck.

I am positive it is coolant.

Yesterday, I did start it up and idle up to temp. I do get some white smoke out of the exhaust. I watched the clear tube running to the recovery bottle and didn't notice any bubbling. I let it sit a while and checked the oil, and it looked ok.

I plan to take it out in a couple days and run it under load a little to see what happens...
 

muc

"Retired" Association of Marine Technicians...
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Jul 7, 2004
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2,064
Re: Mercruiser 6.2 with coolant in oil

The next page in the manual covers what to do if the pressure doesn’t drop. Might want to do those tests.
 

mikedz

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Jun 12, 2013
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Re: Mercruiser 6.2 with coolant in oil

I took it out for a cruise yesterday. It ran fine at 3500 rpm for 10-15 minutes. Temp and oil pressure were normal. I had someone watching the clear tube running to my overflow bottle. There was no bubbling or anything odd...just normal expansion into the bottle.

This morning I re-ran the coolant pressure check after letting the engine warm up a bit. This time the pressure slowly dropped off.
 
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