Calling all diagnostic gurus.
 

Hey guys,
I'm desperate, got our huge 25th anniversary party on this Friday the 10th and need my boat to be ready. One of my motors picked up a bunch of water in the oil. What's the fastest way for me to check what's going on? Oil cooler? head gasket? intake manifold gasket? The motor still starts and runs a little rough; it had run 15-20 minutes before I noticed the problem. The particulars: 38' Scarab, 502's, not sure what vintage or type ( probably bored to 509), TRS drives, approx 500 hp. Thanks in advance. - Jeff

Most likely culprits are blown head gasket, leaking manifolds, or blown oil cooler.

Pull the plugs for a visual and do a compression and leakdown test

You may also have to loop some of the cooling lines to make it a closed system, then pump about 20 pounds of air, and see if it holds the presure and if it does not hold see where it is leaking...NOTE do not put to much air presure in the system, you will blow the intake or other gaskets!!

thanks guys,
I appreciate the help; I just checked the oil cooler and its seems fine. I'll do a visual spark plug test then leakdown. you gotta love the power of oso.- jeff

Cracked head for me. Let go by the number 5 exhaust valve after a hard run. 454 Magnum. Good luck.

Bad exhaust did it for me once long ago.
Took the manifold off put the hose to it and found it right away, ordered new exhaust and was in water 3 days after initial problem.