Pressure Cap: Inspection

Hold the cap in your hand, right side up  . The vent valve at the bottom of the cap should not open. See Fig 1. If the rubber gasket has swollen and prevents the valve from closing, replace the cap. The vent valve should open with a slight pull with your finger nail.

Hold the cap in your hand upside down.  If any light can be seen between vent valve and rubber gasket, replace cap.

Fig 1: Pressure Cap

Courtesy of DAIMLERCHRYSLER CORP.