An ACDelco GM Original Equipment Radiator Cap is a spring loaded cap that seals the radiator filler neck or surge tank, and is a GM-recommended replacement for your vehicles original component. It maintains pressure on the cooling system while the engine is operating, which raises the boiling point of the engine coolant. It also replenishes the system with coolant from the expansion tank (if equipped) when the engine cools off. This original equipment radiator cap has been manufactured to fit your GM vehicle, providing the same performance, durability, and service life you expect from General Motors.