might not own D4 7U

It could be several things like a bad head gasket, a low liner or cracked head. Could be the seat damaged where the chamber wasn,t being sealed by the copper gasket.You may end up taking the head off and going through things step by step.

Would these things not show up with a pressure test. any suggestions on how long i should keep air on the cylinder.

thanks, again

was the radiator pressure tested? I had a radiator that showed no signs of leaking but would foam up and push out of the radiator. Took the radiator in to get it tested and it was all pin holes. Ended up getting a new core.

When the head on my D4C was cracked the coolant had many tiny bubbles come to the surface not big bubbles and didn't push coolant out. Got a reconditioned head from Cat 1500.00 ouch Charlie

How much water does it use how hot does it get and how soon does it staer frothing? Mine has done it since I got it 6 yrs ago but only when its running fast or workining the harder I work it the more it foams but in 5 yrs it hasnt used 2 gal. of water or got over 180 and the cause of mine is Im too lazy to tighten fan belt you can almost spin the fan when stopped so if yours acts like mine you may wanna chech fanbelt,waterpump impellers ohow clen the rad is inside and out

My RD4 does that too when I'm working her hard, but I know I've got a combustion related problem because the water goes black in an hour or two of working. Is your radiator water clear, or black?

When you pressurize a cyl do bubbles appear in the radiator?