Is it necessary to change the engine oil when it turns black?

[PeterLynn]

Engine oil turning black does not necessarily require replacement. The functions of engine oil include the following three points: 1. Lubrication: There is rapid relative sliding between the piston and cylinder, as well as between the main shaft and bearing bush. To prevent excessive wear of parts, an oil film needs to be established between the two sliding surfaces. A sufficiently thick oil film separates the surfaces of the relatively sliding parts, thereby reducing wear; 2. Auxiliary cooling: Due to its lower specific heat value and location inside the engine, where heat energy is generated by fuel combustion, the engine oil can carry heat back to the oil tank during engine operation and then dissipate it into the air, assisting the radiator in cooling the engine; 3. Cleaning: It can carry carbon deposits and sludge from engine parts back to the oil tank through circulation, and flush away dirt generated on the working surfaces of parts through the flow of the lubricating oil.