The engine oil turns black just one day after it was added. Did I buy fake engine oil?
author: Leila
2025-05-07
The engine oil turns black just one day after it was added. Did I buy fake engine oil? No. In fact, the better the engine oil, the faster it may turn black.
The better the quality of the engine oil, the better its cleanliness and dispersibility will be, so high-end engine oil turns black faster than low-end engine oil, and synthetic oil turns black faster than mineral oil.
Why does the engine oil turn black after it is added to the car?
The engine oil washes away the black sludge and metal impurities
The reason why the engine oil turns black is that metal impurities and sludge are generated when the engine is running. These impurities and sludge enter the oil pan with the operation of the engine and deposit, and the engine oil can play a role in cleaning and dispersing.
The cleanliness and dispersibility of the engine oil can inhibit the formation of carbon deposits, oil films, and sludge, and flush the generated sediments into the lubricating oil for removal. Simply put, the engine oil washes away the sludge in the engine oil circuit and some deposited metal impurities in the engine oil pan, so the engine oil turns black. Just like washing clothes, the clothes are clean and the water becomes dirty.
The reason why the engine oil turns black is that metal impurities and sludge are generated when the engine is running. These impurities and sludge enter the oil pan with the operation of the engine and deposit, and the engine oil can play a role in cleaning and dispersing.
The cleanliness and dispersibility of the engine oil can inhibit the formation of carbon deposits, oil films, and sludge, and flush the generated sediments into the lubricating oil for removal. Simply put, the engine oil washes away the sludge in the engine oil circuit and some deposited metal impurities in the engine oil pan, so the engine oil turns black. Just like washing clothes, the clothes are clean and the water becomes dirty.
The engine oil itself oxidizes and turns black
Secondly, when the engine is working, the temperature and pressure are very high, and the engine oil is always circulating in this environment, which will also oxidize and change color. The physical and chemical properties of lubricating oil will change with high-temperature oxidation, high-temperature degradation and fracture. The most obvious change in appearance is the color change. Just like the apples we usually eat, the surface will oxidize and change color after being cut for a few minutes.
Although there are antioxidants in engine oil, antioxidants are not colorants, and they themselves will also make the color of the engine oil darker. Experiments show that DOS (diethylhexyl sebacate) oil samples with added antioxidant NPNA will gradually change from colorless and transparent oil samples to yellow, light brown, and reddish brown after oxidation. The color is getting darker and darker.
The remaining old oil will also make the new oil turn black
Finally, due to the internal structure of the engine, the old oil cannot be completely drained, so once the engine is running, the new oil just added will mix with the remaining old oil, and the oil will turn black. However, a little bit of old oil residue will not affect the performance of the new oil, so don't worry.
In general, it is normal for the oil to turn black, so don't worry too much. As long as the channel for purchasing the oil is regular and the merchant has relevant authoritative test reports, it will be fine.
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