Engines which operate under severe conditions may use an oil cooler to cool the oil in the engine.
In diesel engines, the oil cooler and oil filter are often on the same mounting , on the cylinder block.
The oil cooler is a heat exchanger. It transfers heat from the oil to coolant from the cooling system. Coolant circulates through tubes in the cooler, and oil fed from the lubrication system surrounds the tubes. As the coolant circulates, heat is removed from the oil.
In another design, the oil cooler is mounted in the airstream at the front of the vehicle. This type of oil cooler uses the flow of air passing across its fins to cool the air circulating through it. It is called an oil-to air heat exchanger.