1. Lubricating moving parts
Lubrication is achieved by forming a minuscule barrier layer between moving parts. The lubrication, specifically between the piston rings and cylinder walls, helps to reduce friction, thereby reducing wear. This provides a longer life for the engine and better performance throughout its life.
2. Improving cylinder compression
The lubricating barrier mentioned above fills in any gaps between the piston ring and the cylinder wall. This improves the seal of the cylinder, which helps to improve the ability of the engine to compress the air-fuel mixture and to capture the maximum about of energy from the resulting combustion.
3. Cleaning and preserving
As oil is being produced, a variety of additives are introduced into the formula that help the oil to protect the engine from a variety of different conditions. These can include anti-frothing agents (bubbly liquids include a lot of air, which doesn’t lubricate as well), anti-corrosion agents (which protect against rusting), viscosity modifiers, detergents (which sequester carbon deposits and other insoluble materials in the oil), and pour point depressants (which allow the oil to flow at cold temperatures).
4. Cooling the engine
Oil isn’t as good as water at storing heat (lower specific heat), but it still has a significant conductive cooling effect on the engine via contact with internals and the oil galleries in the engine block. This is in addition to the heat reduction benefit of reducing friction between internal components. Many high-performance cars will feature oil coolers to help maximize this effect.