As your engine continues to run, it'll naturally create and emit a lot of heat. To counter this, a car's cooling system's first line of defense is the thermostat. A vehicle's thermostat is designed to detect if there's too much heat. If that's the case, it'll permit and release coolant to flow from the radiator and have them circulate around your engine to try and cool it down. As the coolant flows around, it'll absorb excess heat from the engine, before circulating back to the radiator. The coolant then flows through the radiator's many small channels and passageways. Here, a heat exchange occurs, as cooling air rushing in from the atmosphere absorbs heat from the coolant. This coolant is now chilled and will flow back into the engine to continue absorbing more heat.