I'm curious, should there be pressure in coolant system when the engine is hot? i cant see bubles during cold start at all but when i start the car with cap removed, coolant level is rising slowly.

 

http://en.wikipedia.org/wiki/Thermal_expansion ?

 

yes

there could be air in your coolant system trying to escape

 

Haha, yes, that's normal. As the coolant gets hotter it expands. If you're not getting burnt off coolant in the exhaust or losing a lot of coolant on a regular basis, I wouldn't worry about the coolant system.

 

I believe that is why they put a 13 psi pressure cap on the cooling system. It is designed to have increased pressure as it heats up. The increased pressure causes a corresponding rise in the boiling point of the coolant. Since vapor doesn't transfer heat as well as liquid, you want your coolant to stay in it's liquid state. Hence the pressurized system.