Pressure Cap: Inspection

Hold the cap in your hand, right side up  . See Fig 1. The vent valve at the bottom of the cap should be normally closed. The vent valve should open with a slight pull with your finger nail. Replace the pressure cap for any of the following:

• Rubber gasket has swollen, preventing the valve from opening, replace the cap.
• Any light can be seen between the vent valve and the rubber gasket.Use only a replacement cap that has a spring to hold the valve shut  .
• Gasket on the bottom of the cap shows noticeable thinning.
• Cap has been through more then one engine overheat.

Fig 1: Cooling System Pressure Cap

Courtesy of DAIMLERCHRYSLER CORP.