Why Do Cars Need Oil Changes?
3 Answers
Car engines require oil changes because over time, the oil can evaporate and deteriorate, losing its original properties. Engine oil, also known as motor oil or engine lubricant, is a substance enhanced with additives in a base oil, primarily containing anti-wear additives, detergents, dispersants, and multi-grade viscosity index improvers. The main functions of engine oil are to reduce friction and wear on moving parts, clean sludge (one function of dispersants) and varnish (detergents) from the engine, neutralize acids produced by fuel combustion and lubricant oxidation (detergents), improve piston ring sealing, and cool the engine by carrying away heat from moving components.
Once, my old car that had been running for seven or eight years suddenly made strange engine noises. The experienced mechanic checked it and said the engine oil was long overdue for a change. Engine oil circulates through the engine like blood, and it mainly does three things: First, it lubricates metal parts—components like the crankshaft and pistons rub against each other thousands of times per minute, and without the protection of an oil film, they’d grind themselves to scrap. Second, it acts as a cleaner—carbon deposits from gasoline combustion mix into the oil, turning fresh golden-clear oil into thick, black sludge; if changed too late, these particles can clog oil passages. Third, it helps dissipate heat—don’t underestimate this one; my neighbor’s turbocharged car had its bearings melt due to degraded oil. Following the manual’s mileage interval is the safest bet, but if you’re often stuck in traffic, changing it 20% earlier gives extra peace of mind.
Last week when I took my sister's grocery-getter car for maintenance, the 4S shop said her engine oil had severe viscosity breakdown. While full synthetic oil can indeed last around 10,000 kilometers nowadays, it depends on driving conditions. For her case - daily school runs of 2 kilometers taking 20 minutes, where the engine barely warms up before arriving - incomplete fuel combustion dilutes the oil viscosity. This situation is like honey mixed with water: neither properly coating metal parts nor effectively carrying contaminants. The mechanic showed me the oil test paper - the diffusion ring edges had completely blurred into jagged patterns. He suggested judging by the dipstick condition: check monthly - whitish means water contamination, black indicates heavy carbon deposits, and metal particles mean immediate oil change is required.
