Radiator Cap (Pressure Cap)

Pressure raises the boiling point of the coolant. A valve releases excess pressure and lets coolant return when the engine cools. The pressure rating is printed on the cap. Pressure testers can check both the cap and the system for leaks. Replacing an old cap is cheap and can solve unexplained coolant loss. Use a cap with the correct pressure rating, as a higher rating can stress hoses and the radiator.

A spring-loaded seal opens at the rated pressure.

A faulty cap can cause overheating or coolant loss. Never open the cap on a hot engine.