Oil in water, but only after shut down

[Leedanger]

4.3L Mercruiser (early 90s). This is a replaced long block due to a crack. Engine runs great, but found milky oil after a year of running it. Thought it was water getting in from up top (down from the cover). Changed oil, ran it...no issues. Next day I come out and the oil is milky. No rain, no sprinklers, and oil was perfect the day before. I've went through this process twice now where the oil was changed, run for 30-40 min with no issues, then the next day it's milky. At a loss, hoping for help. Thanks

 

[alldodge]

Oil turns milky only after the motor is run while water is being mixed with the oil. If water goes into the oil with the motor off, it will just sink to the bottom of the pan.

If your seeing the milk on the dip stick there is four possible locations from my thoughts:
Head gasket, intake gasket, crack block or exhaust manifold.

Suggest start with pulling plugs then check compression. If that checks out, pressurize the cooling system to 15 psi

 

[Leedanger]

Pressurize the cooling system, that's a good idea. J will do that. Thanks.

 

[Rick Stephens]

An exhaust manifold leak would top my list.

 

[flipbro]

An exhaust manifold leak would top my list.

x2.