What does 'adding small oil' mean?

[MatteoDella]

Small oil refers to illegally processed (self-processed and produced) diesel or gasoline, which is cheaper than fuel from gas stations. The following are the hazards of adding small oil: 1. Diesel filter clogging: Once small oil is used for a long time, the diesel filter will become clogged with impurities in the oil, leading to poor fuel supply, reduced power, and other issues. Not only will the replacement cycle of the diesel filter be shortened, but the fuel pump may also be damaged due to clogging by impurities. 2. Fuel injector clogging: Some impurities in small oil adhere to the diesel filter, while others pass directly through the fuel injector without being filtered. Over time, the fuel injector will also become clogged, which not only affects vehicle performance but also causes the fuel injector to fail prematurely. 3. Engine carbon deposits: Impurities in impure diesel will turn into carbon deposits inside the engine cylinders after combustion. When carbon deposits accumulate excessively, the vehicle may experience unstable idling, weak acceleration, increased fuel consumption, and other problems.