Originally Posted by funola

You don't have to own the test equipment. That's why I suggested Autozone. You take the 2 caps you have, screw it onto the tester, pump it up, look at the pressure gauge when it vents and that's the opening pressure. If it does not vent and pressure continue to build, the cap is crap. It takes a minute to test. If the cap is fine, I would clean the seat of the exp tank and check that the vent hose is clear. You can also put the vent hose into a soda bottle to see how much coolant is vented.