An internal combustion engine would not run for even a few minutes if the moving parts
were allowed to make metal-to-metal contact. The heat generated due to the tremendous
amounts of friction would melt the metals, leading to the destruction of the engine. To
prevent this, all moving parts ride on a thin film of oil that is pumped between all the
moving parts of the engine.
Once between the moving parts, the oil serves two purposes. One purpose is to lubricate
the bearing surfaces. The other purpose is to cool the bearings by absorbing the frictiongenerated heat.
The flow of oil to the moving parts is accomplished by the engine's
internal lubricating system.
a suction and pump the oil through one or more oil filters as shown in Figure 12. The
filters clean the oil and remove any metal that the oil has picked up due to wear. The
cleaned oil then flows up into the engine's oil galleries. A pressure relief valve(s)
maintains oil pressure in the galleries and returns oil to the oil pan upon high pressure.
The oil galleries distribute the oil to all the bearing surfaces in the engine.
Once the oil has cooled and lubricated the bearing surfaces, it flows out of the bearing
and gravity-flows back into the oil pan. In medium to large diesel engines, the oil is also
cooled before being distributed into the block. This is accomplished by either an internal
or external oil cooler. The lubrication system also supplies oil to the engine's governor,
which is discussed later in this module.