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Even a new gasket should be considered in regular maintenance.
FYI.... the new caps are designed for 'easy on' and 'easy off'.
Many new caps are made by Stant, and packaged under various brand names, including ACDelco.
According to Stant, all new caps are designed for both 'open' and 'closed' systems.
What I have seen is that radiator caps lose their pressure rating and allow the radiator to boil over when the engine is turned off. You can hear a gurgling sound as the coolant boils into the overflow tank (assuming you have one -- later cars have a remote tank with cap on it).
i test mine every summer. thought i would upgrade to the stant racing one because i thought it is better than the standard one. WRONG. the stant racing looks good and cost three times as much, but fails 1 to 2 psi out of the box and after a few months it was 5 psi off. wrote to stant to find out why it failed so bad and their QA dept didn't catch it or what. never was responded to and questions remain unanswered. I have the best luck with ac delco and also change the thermostat at the same time. a good cap will hold pressure and cause other problems that you may not know of. in my case intake gasket and radiator started to leak. just saying if you don't have any overheating issues, changing an old cap may cause more indepth problems. currently i have the intake off because of this.