raditor cap on 1999 Acura Integra

why does my raditor cap keeb breaking apart between the plunger and cap

Asked by for the 1999 Acura Integra
The cap basically has two valves in it one to relieve pressure and one to recover coolant from the expansion tank. Look at neck in the radiator and the only thing after that I can think of if you had an acidic cooling system due to a blown head gasket the cap can fail. An acidic cooling system often turns the coolant from green to orange rust color.