A radiator helps to eliminate excess heat from the engine. It is part of the engine’s cooling system, which also includes a liquid coolant, hoses to circulate the coolant, a fan, and a thermostat that monitors the coolant temperature. … After the coolant passes through the radiator, it recirculates through the engine.
When the heat causes the pressure in the vehicle’s cooling system to increase above its psi/kPa rating, the radiator cap, by means of a spring-loaded valve, releases some of the coolant from the system into the overflow tank. As coolant exits the system, the pressure drops.