What Engine Oil Does

The crankshaft never quite touches its bearings. As it spins, it drags oil into the narrowing gap beneath it, and that wedge of oil builds enough pressure to lift the shaft and hold it there. You met the same effect on a wet road in the tyre lesson: water dragged under a tyre lifts it off the road. Aquaplaning is a disaster for a tyre and exactly what a bearing wants.

That film is very thin, and it is the only thing keeping metal off metal. As the oil flows past hot parts, it also carries some of their heat away. Its other jobs, keeping the engine clean and protecting it from corrosion, all depend on it getting there.