Functions of oil

Summary
Oil reduces unwanted friction. It reduces wear on moving parts, and helps cool an engine. It also absorbs shock loads and acts as a cleaning agent.

One function of a lubrication system is to reduce friction. Friction occurs between
all surfaces in contact. When moving surfaces come together, friction tends to slow
them down.

Sometimes that’s just what’s wanted. Friction can be useful.

But it can also cause serious damage. It can make metal parts so hot they melt and fuse together. When that happens, an engine is said to have seized.

How long an engine lasts depends to a large extent on how well it’s lubricated, especially at the points of extreme loading.

So lubrication reduces unwanted friction, and controls it where it is useful.

It reduces wear on moving parts. Clearances fill with oil so that engine parts move or float on layers of oil instead of directly on each other. Much less power is needed to move them and that’s a plus.

It helps cool an engine. It collects heat from the engine, then returns to the sump, where it cools.

It helps absorb shock loads. A power stroke can suddenly put as much as 2 tonnes force on main bearings. Layers of oil cushion this loading.

Oil is also a cleaning agent. It collects particles of metal and carbon and carries them back to the sump. Larger pieces fall to the bottom.

reference
CDX