Engine oil viscosity drops are usually contaminated by fuel oil. There are many reasons for fuel oil pollution, mainly in the following aspects:

(1) The fuel supply system is not working properly, and the fuel atomization is not good, which will cause the fuel or a large amount of excessively rich fuel mixture to be mixed into the crankcase to mix with the oil to dilute the oil.

(2) The engine idles for a long time, and it does not turn on the vehicle when it is repeatedly started. It will cause the fuel mixture to enter the crankcase.

(3) Oil leakage from the fuel injection pump or the oil pump will also make the oil diluted by the fuel.

(4) The oil has not been changed for a long time, and the fuel gradually accumulates in the oil.

(5) The engine starts and stops frequently and cannot run continuously under stable conditions, which will cause the fuel to not evaporate from the oil and gradually accumulate.

(6) If the cylinder wall of the engine is worn, the piston ring is damaged or the piston ring is improperly installed, the gap between the cylinder liner and the piston friction pair is increased, and the fuel enters the crankcase to dilute the oil.

When the engine oil is polluted by fuel, it will have adverse effects on the anti-wear and anti-corrosion of the engine. When the diesel engine oil contains more than 5% of fuel, it is recommended to change the oil. The changed oil can be filtered by a filter oil machine, and the oil can be used continuously.