2.0L / 2.7L

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 cap for any of the following conditions:

1. Rubber gasket has swollen, preventing the valve from opening
2. 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 vent shut. 
3. Gasket on the bottom of the cap shows noticeable thinning
4. Cap has been through more than one engine overheat.

Fig 1: Identifying Radiator Pressure Cap - Typical

Courtesy of DAIMLERCHRYSLER CORP.