overflow cap adapter

[Pendaflex]

I am working on a 2004 Carver with 2 6.0L GM engines. I want to pressure test the antifreeze side of the cooling system. I have 16 different adapters for my pressure tester but none fit. I have called a couple Pleasurecraft dealers/repair facilities and none will take the time to answer my question. Does anyone know where I could purchase the adapter as it looks like a GM style reservoir but the GM adapter is too large. I have an overheating problem and loss of coolant. The exhaust manifolds and risers are new, the heat exchanger is new. The heads have been off pressured tested to 45psi, resurfaced and dye tested. New factory thermostat, water pump">raw water pump has good flow. The engine also fails the combustion(dye) leak detection exhaust in the cooling system test. The machine thinks it is corrosion around the water ports. Thanks in advance.

[RaymondR]

Risky business pressure testing.

Why not locate the drain plug and connect into the cooling system there. That way you don't risk over pressuring because the filler cap will act as a pressure relief valve.

[a64pilot]

Failing the combustion test, is awfully indicative of head gaskets. It means of course that combustion gasses are in the coolant, you have to ask yourself where could that happen?
Pretty much the heads or gaskets, possible but unlikely a cracked sleeve in a block?
These are dry sleeve motors so that so unlikely as to be almost impossible?

I don’t understand what the machine thinks it’s corrosion around the water ports means?
Machinist maybe? Which water ports? Ones in the block?

[Pendaflex]

Thanks for the reply. Yes machine shop thinks there is too much corrosion on the surface of heads, too extensive to cut out. Going to look at the block today, engine is 150 miles away from me at Remlik Mariner