Why is it necessary to change engine oil?

[ConnorLee]

Replacing engine oil is necessary because: if the oil is not changed for a long time, its performance will degrade and its effectiveness will diminish. Symptoms of insufficient engine oil in a car include: 1. Insufficient lubrication due to splashing of engine oil inside the engine; 2. Burning of the crankshaft bearings and bearing bush due to poor lubrication; 3. Abnormal engine vibration and reduced power; 4. Malfunctioning of the engine's variable timing solenoid valve. Engine oil, also known as engine lubricant, serves to lubricate and reduce friction, assist in cooling, seal against leaks, prevent rust and corrosion, and act as a shock absorber in the engine. It is composed of base oil and additives, with the base oil being the main component that determines the fundamental properties of the lubricant.