Why Does Engine Oil Turn Black?

[LaTaylor]

Engine oil turns black for the following reasons: Incomplete Combustion: Incomplete combustion of engine oil, especially prone to forming black sludge, poor air filter filtration quality, and excessively high engine temperatures causing oil oxidation to produce gums and carbon deposits. High-Power High-Temperature Operation: Prolonged high-power, high-temperature operation of the engine under overload conditions oxidizes the oil and turns it black, not cleaning the engine or replacing the oil filter when changing the oil. Incomplete Drainage of Used Oil: Adding new oil without completely draining the old oil contaminates the new oil, as the cleaning function of the new oil washes down existing gums, carbon deposits, and sludge inside the engine, mixing them into the oil and turning it black. Low-Quality Diesel: Using low-quality diesel causes the engine oil to turn gray or white after some use, mainly due to water mixing in during oil filling or usage, leading to oil emulsification.