Radiator Caps

Radiator caps maintain cooling system pressure, raising the boiling point of coolant, and allow coolant to return from the overflow tank as the engine cools. A weak cap can cause boil-over and coolant loss; a cap that does not vent correctly can collapse hoses or crack tanks.

Caps are specified by pressure rating (in kPa or bar), neck style (shallow or deep, radiator or expansion tank thread) and vacuum valve design. Pressure ratings must match the vehicle; fitting a higher-pressure cap to resolve boiling can overstress radiator tanks and hoses. Caps are small, low-cost and easy to add to a mixed shipment alongside radiators.