When, and how often, should I replace the radiator cap?

[galant]

It won’t blow, it would start leaking or rather not holding pressure and you loose coolant. Rarely an emergency if you are in the habit of checking under the hood once a week. My Caravan’s cap decided to go last week at 106KM, so 100KM sounds about right. I noticed some whitish dried stuff around the cap after the coolant had dried.