Internal combustion engines need lubricant in order to operate. In cars, that lubricant is known appropriately as motor oil. The key measure of a motor oil is its viscosity. When heated, motor oil tends to lose its viscosity; if the oil is heated far enough, it will thin out enough that it cannot serve its primary function of lubricating the engine's moving parts.

Lubrication, however, is not oil's only function. It also serves as a coolant, transporting heat from inside the engine block to the oil pan, where it can be dissipated into the surrounding air. Problems arise when an engine is running fast enough and hot enough that the oil is never left in the pan long enough to properly cool. This usually happens suddenly, since engine temperatures rise with increased engine revs. As a result, engines that run fast and long are vulnerable to oil breakdown.

The oil cooler is one solution. An oil cooler is nothing more complicated than a separate radiator dedicated to the engine's oil supply. An oil line is run (usually from the oil filter adapter) to the oil cooler, which is placed somewhere in the flow of outside (cooler) air, such as behind the engine fan. Oil leaves the engine and then runs to the cooler, which is typically a finned metal block with passages through it for the oil. The increased surface area and cooler airflow cools the oil more quickly than the oil pan, and the oil (and engine) can withstand higher heat.