Cap, Radiator: Inspection

Hold the cap at eye level, with the vent valve pointing down. The vent valve at the bottom should open. If the rubber gasket is swollen and prevents the vent valve from opening, replace the cap.

Hold the cap at eye level, with the vent valve pointing up. If any light can be seen between the vent valve and the rubber gasket, replace the cap. Do not use a replacement cap that has a spring to hold vent shut.  A replacement cap must be the type designed for a coolant reserve/overflow system with a completely sealed diaphragm spring and a rubber gasket. This gasket is used to seal to radiator filler neck top surface. Use of proper cap will allow coolant to return to the radiator.