Although it is the fuel system (mixing fuel and air to flow into the cylinders) that makes our engines work, the lubrication system of a combustion engine makes sure that every moving part gets oil so that it can work easily.
The two main parts needing oil are the pistons (so they can slide easily in their cylinders) and any bearings that allow things like the crankshaft and camshafts to rotate freely. In most vehicles, oil is sucked out of the oil pan by the oil pump, run through the oil filter to remove any grit, and then squirted under high pressure onto bearings and the cylinder walls. The oil then trickles down into the sump, where it is collected again and the cycle repeats.
Oil collects contaminants from the combusting air and fuel in the engine. Exhaust gases can blow past the rings, dumping combustion products into your oil. These contaminants include fuel, acids, soot, and
water vapor. These materials react with the oil and the additives, causing sludge, varnish, oil thickening and acid formation.
Some engine oils are formulated with detergents, dispersants and antioxidants to resist the effects of these contaminants, but eventually they too will be depleted. Oil effectively breaks down as it ages and loses the ability to lubricate so old oil must be regularly drained from the engine and replaced with new oil.
In colder climates or during the winter, increased condensation can cause engines to burn oil at a faster rate. Consistently changing your oil will contribute to safer driving, longer vehicle life and better overall engine performance.