Water in oil
 

Whats the best way to determin the source of water in the oil? Is there some way to pressure check a non closed system ?

#1 manifolds or risers. remove from engine and pressure test. #2 Intake and heads remove from engine and check gaskets for failure. #3 block, when intake is off check for cracks in lifter galley

You did not say what kind of power you had in the boat. I just had to replace my stock risers on a pair of HP 500s for a pair with about a 9inch rise because i was getting water ingestion on th strbd motor. Its a cam thing on the HPs. Went through about 400 dollors worth of oil on that motor before the guys at AtoZ marine told me what the problem was. No more problems.

Had to do this myself recently. If you need to pressure test your water system, best place to start is by blocking off the exhaust hoses. Pull the hoses off the exhaust risers and either loop them back on themselves or just put a 'plug' in the hose. Then use your house water in the raw water intake hose to pressurize the system. Watch your water pressure gauge, I use a ball valve to slowly pressurize the engine up to about 20-25 psi and the listen/watch for leaks, your residential supply should be around 35-40 psi, hence the reason for the valve. Pull the spark plugs out before you do this, so if its the head gaskets you'll see the water coming out of the cylinders. If your don't immediately find a leak, leave it sit for awhile and check back off and on.