Why is the engine oil black when drained?

[VonElliana]

The reason why the engine oil turns black when drained is due to not changing the oil in time. The functions of engine oil are: 1. To alleviate friction and high temperatures; 2. To reduce gas leakage and prevent external pollutants; 3. To prevent contact between water, air, acidic harmful gases, and engine parts; 4. To buffer the pressure rise in the engine cylinder ports; 5. To flush away dirt generated on the working surfaces of parts. The method for changing engine oil is: 1. Lift the car and remove the bottom guard plate; 2. Place an oil container under the oil pan and loosen the drain plug; 3. After the oil is completely drained, replace the oil filter and apply a layer of oil around it; 4. Tighten the drain plug, reinstall the guard plate, lower the car, and pour in the new engine oil.