Why does engine oil need to be changed?

[AngelaFitz]

Engine oil needs to be changed for the following reasons: 1. Engine oil has a shelf life, and over time its performance degrades, leading to accelerated wear of mechanical components; 2. After undergoing high-temperature operation within the engine, the physical and chemical properties of engine oil change, consequently altering its mechanical properties; 3. With prolonged engine operation, impurities in the oil increase, which can accelerate the wear rate of mechanical parts. The functions of engine oil are: 1. To reduce wear between the piston and cylinder, as well as between the main shaft and bearing bush, providing lubrication; 2. To assist in cooling the engine internally; 3. To clean carbon deposits, sludge, and wear metal particle impurities from engine components; 4. To reduce gas leakage and prevent external pollutants from entering; 5. To cushion and absorb shocks, reducing the load on pistons, piston rings, connecting rods, and crankshaft bearings.