Firstly, the blackening of lubricating oil is related to the fuel used. The higher the olefin and sulfur content in the fuel, the easier it is to form sludge.

Secondly, when changing the lubricating oil, do not clean the inside of the engine and the oil pan. The sludge in the previously used lubricating oil deposits in the oil pan and inside the engine. After adding new lubricating oil, due to the effect of the cleaning dispersant, some sludge, carbon deposits, and glue inside the engine are cleaned and dispersed making it black.

Furthermore, after oil change, the high temperature of the engine caused the lubricating oil to oxidize and turn into a gum like substance. Due to the effect of the detergent dispersant in the new lubricating oil, it became suspended in the lubricating oil and turned black.

In addition, the blackening of lubricating oil is also related to the quality and replacement cycle of the lubricating oil filter and air filter. If the air filter is of poor quality or not replaced in a timely manner, dust and impurities will enter the cylinder and adhere to the cylinder wall, then mix with the lubricating oil to contaminate the lubricating oil.

Poor quality oil may turn black shortly after use, it has poor antioxidant and high-temperature resistance, making it prone to deterioration. However, blackening of lubricating oil may not necessarily be due to poor lubricating oil quality, as good lubricating oil contains an efficient cleaning and dispersing agent that can clean and disperse the gum, paint film, carbon deposits, etc. that previously existed inside the engine, making them suspended in new oil and making the oil more prone to turning black.