Oil, passing through the operating engine, absorbs heat from the metal parts. Since engine oil is recirculated and used over and over, it is continually absorbing additional heat. Unless the heat is removed, the oil temperature will rise to excessive values. At extremely high temperatures, oil tends to oxidize rapidly and form carbon deposits.
Excessive engine operating temperatures also cause an increase in the rate of oil consumption.
Consequently, oil coolers are required to remove excess heat from the oil so that the oil will retain its lubricating qualities. The coolers used to remove heat from lubricating oil are of the same type as those used to remove heat from other fluids common to internal-combustion engines. These coolers are referred to as shell and tube, strut tube, or plate tube coolers. Oil must also be cleaned regularly while it is being recirculated through the engine. Dust and dirt particles from the intake air get into the oil system.