Why Do Cars Need Oil Changes?

[DiDominic]

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.

[McGrace]

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.

[VonAlexis]

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.

[LaLily]

While repairing the transmission, I noticed the apprentice forgot to reset the maintenance light, which reminded me how interesting the oil life monitoring principle is. Nowadays, new vehicles use oil quality sensors to monitor three key indicators: conductivity to detect impurity concentration, viscosity sensors to measure flow speed, and dielectric constant to reflect water content. Once, while handling an out-of-warranty complaint, I discovered the customer had used the wrong oil grade. For instance, German cars require 40 viscosity, but he used 20 viscosity, resulting in oil film that was too thin and camshafts with visible wear marks. Changing oil isn't just about pouring in new oil; it also involves replacing the filter and sealing gaskets simultaneously. Especially for some vehicles where the filter is located under the chassis, roadside shops often forget to install the sealing ring.

[DiMakayla]

It wasn't until the oil temperature soared to 150°C during the last track day that I truly understood the importance of engine oil. When conventional oil thins out at high temperatures, the oil pump delivers 30% less volume. My oil pan camera captured piston skirts completely devoid of oil film protection. Switching to racing oil solved the issue, but daily drivers must pay equal attention to low-temperature fluidity. Using 0W oil in northern winters makes morning startups noticeably smoother - old oil turning to jelly in cold weather is what really damages engines. Turbocharged cars demand even more frequent oil changes. A friend's Golf GTI suffered turbo bearing seizure; disassembly revealed carbon particles from degraded oil had infiltrated the bearing clearance.

[Sara]

An old pickup truck driver who frequently works on construction sites taught me a folk trick: every 5,000 kilometers, drip some engine oil and examine it under a UV light from a counterfeit detector. Fresh oil fluoresces green, indicating sufficient additives, while old oil turns brownish-yellow, signaling depleted antioxidants. The difference between mineral oil and synthetic oil is like that between rapeseed oil and olive oil—the latter has a more uniform molecular structure and resists breakdown under high temperatures. I once disassembled an engine that hadn’t had an oil change in 100,000 kilometers; sludge had clogged the oil passages like asphalt and sealed the crankcase ventilation valve. The overhaul cost 8,000 yuan, enough for 40 years’ worth of oil changes. My advice: don’t wait for the dashboard alert—replace the oil when it’s at 70% lifespan to best protect your engine.