Quote Originally Posted by wbute View Post
That's not right. Running a radiator at higher pressure causes the coolant to have a higher boiling point. There is more advantage than not losing coolant.
The pressure the cap vents at is independent of whether or not you have a recovery system. The pressure the cooling system runs at is set by the engine designers and affects the type of seals and gaskets used in the engine. Thats why different pressures for 6, 8, Ford GM etc. You can have a low pressure cap on one engine and still have a recovery system so you don't vent to ground.

When you don't have recovery, the radiator vents an inch or so of fluid out of the header tank and then finds an equilibrium so that when you keep checking there is always about an inch or so missing. This is under normal running. This can change if you tow or otherwise load up the cooling system. That's why I'm pretty sure A/C cars used to run slightly more pressure.