What Causes Engine Oil to Turn Black?
2 Answers
Engine oil turns black due to: 1. Poor fuel quality; 2. Prolonged high-temperature operation of the engine under overload conditions; 3. Failure to replace the oil filter and air filter in a timely manner. Solutions to prevent engine oil from turning black include: 1. Using higher-quality fuel; 2. Avoiding prolonged high-temperature operation of the engine under overload conditions; 3. Replacing the oil filter and air filter promptly. The functions of engine oil are: 1. To separate the surfaces of relatively sliding parts, thereby reducing wear; 2. To carry heat back to the oil tank and dissipate it into the air, assisting the radiator in cooling the engine; 3. To circulate carbon deposits, sludge, and metal wear particles from engine parts back to the oil tank, flushing away contaminants generated on the working surfaces of parts through the flow of the lubricating oil.
Engine oil turning black is primarily a result of normal wear during its operation inside the engine. Like when I perform car maintenance in the garage, I always check the dipstick—fresh oil has an amber color, but after a few thousand kilometers, the high temperatures in the engine cause the oil to oxidize and darken, mixing with carbon particles and soot from combustion residues. This is as natural as dust accumulation. Additionally, impurities generated from the friction of the engine's metal components are carried away by the oil, making it progressively darker. This isn’t always a bad thing; it indicates the oil is doing its job. However, if the oil darkens too quickly or loses viscosity, it may suggest incomplete combustion or a clogged filter, affecting lubrication efficiency. That’s why I often remind my friends: regular oil changes are crucial. Follow the manual’s recommendation—replace the oil every 5,000 kilometers or six months—and don’t just rely on color; also test the viscosity to ensure it’s normal. This way, the engine’s lifespan will be extended.
