In the modern diesel engine, engine oil must perform four basic tasks without having a negative impact on engine performance and longevity of the engine. These functions of the oil are discussed here.
The engine oil provides a film of protection between the moving parts of the engine. This oil film reduces friction, wear, and heat in the engine. In order to maintain the proper thickness of this oil film the engine must run at the correct temperature, the engine oil pump must produce the correct pressure, and the oil must have the correct viscosity.
The combustion that takes place in the engine produces a tremendous amount of heat, especially on the pistons. The engine oil is the primary cooling agent for the pistons. Much of the heat is removed by the oil that is between the cylinder wall and the piston and by “splash” oil thrown off moving parts. Additionally, many engines have piston cooling jets that spray oil at the underside of the pistons, providing a tremendous cooling effect to the pistons. This is a primary reason that engine oil is required to withstand high temperatures without losing its properties.
As the engine operates there will be some amount of blowby. There will also be some amount of foreign debris in the engine from one source or another. It is the responsibility of the engine oil to carry the contaminants out of the moving engine components, so that the contaminants will be cleansed from the system by the engine oil filter. This is especially important in the engines equipped with the HEUI fuel system. The HEUI fuel system uses engine oil to operate. The engine oil helps to keep contaminants from collecting in the engine.
The engine oil creates a film between the piston rings and the cylinder walls. This film not only lubricates, but also helps to seal the combustion chamber of the engine off from the crankcase. This helps to prevent blowby.