Can Mixing Oils Be Harmful to Diesel Engine？

Motor oil plays the role of lubrication, cooling, cleaning and sealing in diesel engine. There are differences in the composition and performance of different types and sizes of motor oil. Mixing motor oils may cause various hazards to diesel engine.

First, it affects lubrication. The viscosity of motor oil is a key performance indicator. When oils with different viscosities are mixed, the viscosity may deviate from the range required by the engine. If the viscosity decreases, the oil film is easy to rupture, can not effectively isolate moving parts, resulting in increased friction. If the viscosity increases, the fluidity of the oil becomes poor, the lubrication is not timely when the engine starts, and the wear of the parts will be aggravated. For example, mixing low-viscosity oil with high-viscosity oil may make the oil insufficiently viscous at high temperatures to protect high-speed moving parts such as pistons and cylinder walls.

Second, a chemical reaction may be triggered. Different brands or types of motor oil have different additive compositions. There are differences in the base oil compositions of mineral oil, semi-synthetic oil and fully synthetic oil, and the types and proportions of additives may also be different. When mixed, the additives may react chemically and produce deposits or gums. These substances can clog oil filters and oil passages, resulting in blocked oil circulation and inadequate lubrication of key engine components. At the same time, the precipitate will also adhere to pistons, valves and other components, affecting their normal operation.

Furthermore, it will reduce the cleaning and dispersing ability. High-quality oil can adsorb carbon, sludge and other impurities inside the engine, and will be dispersed in the oil, filtered through the filter. Mixing oils may destroy this ability and allow impurities to be deposited inside the engine. Excessive carbon deposits can affect fuel combustion efficiency, and sludge clogging oil passages can cause parts to overheat and shorten engine life.

In addition, sealing performance may be affected. Oil enhances sealing by forming an oil film on the seal surface. Mixing oils may cause seals to expand or contract. For example, additives in some oils may react with the seal material, hardening or softening the seal and causing an oil leak. Oil leakage not only reduces the amount of oil, but may also contaminate other engine parts and cause more serious malfunctions.

Practice shows that the piston ring wear rate of a diesel engine with long-term oil mixing is more than 30% faster than that of an engine using a single oil, and the probability of oil passage blockage also increases significantly. Therefore, in order to avoid jeopardizing the diesel engine, you should use the same brand and specification of engine oil, try to empty the old oil when replacing the engine oil, and do not mix different types of engine oil at will.