The water tank can be used to heat water. Drain the water from the water tank and heat the water. This can heat the engine and make it easier to start. The car water tank is called the radiator and is a component in the car cooling system. The function is to dissipate heat. The cooling water absorbs heat in the water jacket. After flowing to the radiator, the heat is dissipated and returned to the water jacket for circulation to achieve temperature regulation.