Have a 500 hp. Port engine built a bunch of water pressure and blew water line off. Got it shut down before it got over 170 deg. Checked oil and it had about 3 quarts of water in it. Tour it down and had heads checked. They are fine. Gaskets all looked fine. Exhaust is fine. No reversion. Put all back together and still building water pressure and getting a lot of water in oil. Oil cooler is fine. Out of ideas except a cracked block for some reason. Any ideas?

first question, why are you building water pressure?? either its too much in or not enough out. Figure that one out first.

Have checked everything that I can think of for increased water pressure. This boat has been running for years. I'm wondering if I have a cracked block and have compression leaking into water system

Have you checked the thermostat and circulator pump? Is the intake leaking ?

I run small blowers so I don't have a circulation pump I run a crossover with no thermostat. Have a eikert water pump. I was wondering if my intake would of cracked for some reason if that would allow increased water pressure.

How much water pressure are you seeing on the port engine vs starboard ?

They used to run the same. Now it's running according to Gage's 15 pounds more. Frustrated

That's a lot of variation between engines. Something that comes to mind that will increase water pressure is a blockage of some type in the way the water exits the engine. Possibly a restriction in the water passages in the exhaust, or in the t-stat housing? do your engines have those check balls coming off the t-stat housing?

No they do not. I have gill exhaust and checked exhaust pipes with garden hose and they seem to be flowing the same as other side. When both motors running they appear to be the same on exhaust pipes and out the dumps. It also has supper chillers. Does anyone know if a cracked block or intake manifold could allow compression into water and increase pressure?

We had a similar issue with my brother in law's 500hp 396 in his Chevelle. It ended up being a cracked #2 cylinder wall, pressurizing the water jacket. It was cracked low on the cylinder wall. Had to rotate engine to bottom of stroke to see the crack. Might be the same issue you have.

Good luck