Water in engine oil.

Checked my engine today for the first time since I put the boat in the water at the beginning of June. The oil is milky. Obviously water is getting in somewhere. Did not have this problem last year or at the beginning of this year. The engine is a Mercruiser 165 (GM 250) in line six. It is 42 years old. The only thing on the engine that hasn't been replaced is the block (and internals) and the head. It is raw water cooled. No heat exchanger. All new exhaust manifold and exhaust/cooling system parts. All bellows and gaskets on sterndrive and so on. It is only used in fresh water. And, the engine runs very well. Reaches max rpm at WOT and does 30-35 mph.

Anyway here is my plan.

remove old oil and replace.
replace oil filter.
remove plugs one at a time, look for water, and crank to see if there is water in the cylinders.
check compression on each cylinder
run engine until it gets up to normal temp and run it for ten minutes or more.
drain and change oil and filter again
run engine
check oil for water.

I suspect a leaking head gasket (had that problem with another engine) but no white smoke in exhaust.

Worst scenario, cracked head or block.

Have I forgotten anything I should check or left out a step?
Any other suggestions, advice?

 

Those early engines were known to blow head gaskets. Maybe it was the gasket material and it won't happen with the new "not retorque" gaskets.

 

Thanks Gonzo. I am hoping that is all that it is. On this engine changing a head gasket is relatively easy, and since it doesn't seem to be getting water in the cylinders, just the oil, I suspect that it is the gasket.

 

Check the cover of the timing chain. It sits right under the water pump.
My old Mercruiser developed a few tiny holes and the water pump seal leaked a bit, exactly on those holes.
Much easier to repair than changing the head gasket, although the cover turned out to be a very expensive piece of iron.

 

Changed oil and filter. Ran engine for about 15 minutes.
Changed oil and filter again. Oil is still slightly milky but clear.
There is a small amount of water coming out of the manifold gasket just forward of the carb, right about where one of the bolts for the manifold is located. When the engine heats up the leak stops (at least on the outside). I checked the torque on the bolts and two were not as tight as the others. There are no other visual leaks. There is no water in the cylinders so I am now thinking (and hoping) it is just the manifold gasket

checked plugs and compression
cylinder
1 dry plug looks good 125#
2 dry looks good 120#
3 slight amount of oil, no water, 120#
4 slight amount of oil, no water, 120#
5 dry looks good 120#
6 dry looks good 120#

The engine runs well. However, it does not seem to be warming up to normal operating temps. I shot it with a infrared heat gun and temp was about 103 deg F, a lot cooler than it should be. I think the thermostat is stuck open.

 

The headbolts go through to the waterjacket. If water seeps through, the sealant is probably dried up.

 

Turned out to be a leaky gasket between the Riser and the exhaust manifold. All fixed. Cost $306.50 almost all labor. The gasket was $3.46.

 

Too bad it wasn't a closed cooling system. My old farm book said you can fix that kind of problem by putting a few raw eggs and a bunch of pepper into the radiator. Not that I'd try that, but one time I did pour a pint of hydrogen peroxide into my trucks carburetor while it was running, under the suggested theory that it was mostly oxygen and it would burn up all the carbon deposits in the cylinders and spit them out the exhaust. The truck had a hard time with that and I don't think the peroxide did what it was supposed to, but at least the truck still ran after that.