The radiator plays a critical function in all internal combustion engines as it help keeps a vehicle from overheating. It is connected to several channels running through the engine and cylinder head, through which is pumped a liquid which is usually a mixture of water with ethylene glycol (antifreeze). The liquid then flows through a thermostat and back again to the radiator. As such, heat is conducted away from the engine parts, making the vehicle safe from overheating.

To keep the radiator, the fluid inside, and the engine in peak conditions, the radiator is typically mounted behind the vehicle's grille, as cold air is driven through it. There is also a system of valves installed to simultaneously operate a small radiator called the heater core inside the car. This small radiator serves to warm the vehicle's interior cabin.

A device located between the engine and the radiator called the thermostat is another key component of a vehicle's cooling system. The thermostat remains closed and restricts coolant flow until the engine reaches the thermostat's activation temperature. This enables the engine temperature to remain in the ideal operating range. The thermostat closes and allows heat to build up in the engine when the engine gets too cold and it opens and allows heat to be removed by the radiator when the engine becomes too warm.

The invention of the radiator is widely attributed to Karl Benz. Nowadays, some engines have an additional oil cooler which is a separate small radiator to cool the motor oil while most turbo-charged engines may even have an intercooler.