Will a coolant pressure test show a blown head gasket?

Yes. Not only does coolant travel through the radiator and hoses, but it also works its way through passages inside your engine. Those passageways are kept separate from the combustion chambers and crankcase by gaskets. If the head gasket or intake manifold gasket are bad, coolant can leak internally. A pressure test can indicate a leak, even if it is not apparent exactly where the leak is located. It can also suggest a cracked or warped head.

How much pressure is in a car cooling system?

Typically, the radiator cap is responsible for maintaining a consistent pressure in the cooling system. When the coolant gets too hot, it produces steam and pressure. The radiator cap is a type of pressure relief valve, usually set to hold up to about 15 psi of pressure in the system.

Can coolant run low without a leak?

It is possible for your engine coolant to run a bit low over time, even if there is no visible leak. Evaporation from the overflow tank is possible, so there is a fluid level indicator on the side of the tank to let you know when to top it off with coolant. But there are other reasons that your engine seems to be low on coolant, such as an internal leak that allows some of the coolant to be burned off in the combustion process. That can indicate a serious problem, such as a blown gasket or cracked manifold.