Radiator Cap: Service and Repair

Hold the cap in your hand, right side up. The vent valve at the bottom of the cap should open with a slight pull. If the rubber gasket has swollen, preventing the valve from opening, replace the cap.
If any light can be seen between vent valve and the rubber gasket, replace the cap. Use only a replacement cap that has a spring to hold the vent shut.
A replacement cap must be of the type designed for coolant reserve systems. This design ensures system pressurization.