cooling system to much pressure!

Check for any clogging, maybe you could have restricted flow of coolant?

Thanks Dane. Do you think partial clogs in core or radiator would be enough?.
I have flushed both but radiator did not seem to be flowing as freely as I've seen on others I have flushed.

how are you identifying that you have too much pressure?
it's pretty common for the overflow cap to fail. have you replaced it?

I'm thinking the same thing. The system can't build up too much pressure. Once it hits the psi marked on the cap it blows by. Have you changed your cap

RE-test for combustion gases...

something clogged could bring up your pressure, like if your radiator was clogged real bad, you could spring a leak somewhere or blow your cap under load. Also, x2 on what PT said, good idea to double check that.

The cap is spring loaded set to18psi - iirc. If pressure rises above this it leaks by The seal and out of Tue overflow tube making it very hard to blow a cap and equally hard to build any pressure past this point.

I agree with the chemical block test. If a head gasket was causing it to boil out it should show up there. Also, again, the cap itself is a good place to start for these situations. 1psi lost through the cap seal reduces the boiling point of the coolant by 10 degrees.