Radiators are used for cooling internal combustion engines, mainly in automobiles but also in piston-engined aircraft, railway locomotives, motorcycles, stationary generating plants and other places where such engines are used.

To cool down the engine, a coolant is passed through the engine block, where it absorbs heat from the engine. The hot coolant is then fed into the inlet tank of the radiator (located either on the top of the radiator, or along one side), from which it is distributed across the radiator core through tubes to another tank on the opposite end of the radiator. As the coolant passes through the radiator tubes on its way to the opposite tank, it transfers much of its heat to the tubes which, in turn, transfer the heat to the fins that are lodged between each row of tubes. The fins then release the heat to the ambient air. Fins are used to greatly increase the contact surface of the tubes to the air, thus increasing the exchange efficiency. The cooled coolant is fed back to the engine, and the cycle repeats. Normally, the radiator does not reduce the temperature of the coolant back to ambient air temperature, but it is still sufficiently cooled to keep the engine from overheating.

This coolant is usually water-based, with the addition of glycols to prevent freezing and other additives to limit corrosion, erosion and cavitation. However, the coolant may also be an oil. The first engines used thermosiphons to circulate the coolant; today, however, all but the smallest engines use pumps.


Intercoolers increase the efficiency of the induction system by reducing induction air heat created by the supercharger or turbocharger and promoting more thorough combustion. This removes the heat of compression (i.e., the temperature rise) that occurs in any gas when its pressure is raised (i.e. its unit mass per unit volume - density - is increased).

A decrease in intake air charge temperature sustains use of a more dense intake charge into the engine, as a result of forced induction. The lowering of the intake charge air temperature also eliminates the danger of pre-detonation (knock) of the fuel/air charge prior to timed spark ignition. This preserves the benefits of more fuel/air burn per engine cycle, increasing the output of the engine.

Intercoolers also eliminate the need for using the wasteful method of lowering intake charge temperature by the injection of excess fuel into the cylinders' air induction chambers, to cool the intake air charge, prior to its flowing into the cylinders. This wasteful practice (before intercoolers were used) nearly eliminated the gain in engine efficiency from forced induction, but was necessitated by the greater need to prevent at all costs the engine damage that pre-detonation engine knocking causes.[2]