high pressure in cooling system

[jarekt]

I'm wonder if anyone can help diagnose high pressure of gases in cooling system.
Car is running great, still after approx 100 miles on HWY temp is going up.
I can't see any oil in coolant or coolant in oil system. Still there's very high pressure of gases (air?). To be more specific, driving on 5th, 100m/h is not a problem, only as soon as i idle engine, temperature is going up. accelerating will bring tmp down again. When engine stop, there's a lot of spill from overflow tank and i can release a lot of steam from radiator!. When engine is cool, coolant from overflow will go back to radiator.
There's not "white" smoke from pipe, no lost power.
one more: on old engine i have "burbling" noise in core heater. This sound didn't go away when i installed new engine two years ago.

Any ideas?
BTW When it happed first time, i replaced thermostat.

[IHateHacks]

Your head gasket is leaking. Actually, the head gasket is warped around the exhaust side cooling passages.

But you don't have to take my word for it. Run a block test to confirm

[jarekt]

how i can run block test? just cylinder pressure?

[mrnickleye]

No. Have a shop perform it. It is a special liquid that is used at the radiator top, and can tell if gasket is blown.

OR/AND....the radiator top can be sniffed by an exhaust gas analyser. Hydrocarbons means exhaust gasses in the cooling system....means BHG.

PS: Your symptoms are exactly what mine were, $800, my labor, 2 1/2 yrs ago.