Caps are typically manufactured from zinc plated steel or stainless steel where fitted directly to the radiator, while for higher operating pressures, a different type of pressure caps, generally manufactured from plastic, are available. The function, and importance, of the radiator/expansion tank cap within a cooling system often goes unrecognised, yet it is a fundamental component. Invariably the replacement of a radiator cap is a simple and rapid fix for many coolant pressure problems. Integral to the fault-finding process, should be the replacement of an obvious component part such as the radiator cap/pressure cap.