Corrosion/noise reduction in the lubrication system
Engine oil performs many other functions apart from lubricating moving components. Two other functions are corrosion protection and noise suppression.
Corrosion protection
Acids build up in the engine due to the accumulation of combustion by-products and moisture.
Blow-by gasses contain chemicals that are trapped in the oil. The chemicals react and form acids.
When the engine is turned off it begins to cool. As it cools, fresh air that contains small amounts of moisture is drawn into the crankcase via the PCV system. The moisture condenses into droplets that fall into the oil and form acids.
The acids attack the internal components causing unnecessary damage. The oil contains anti-corrosion additives that coat the engine surfaces, protecting them from the effects of the acid.
Noise suppression
As oil is pumped through the engine it is forced between moving components. This protects the components from wear and acts as a shock absorber dampening the shock loads between those parts and quietening the engine operation. The oil also coats all the internal walls of the engine providing an insulating barrier to noise.
