Engine oil, also known as engine lubricant, has a density of approximately 0.91×103 (kg/m3). It serves functions such as lubrication and wear reduction, auxiliary cooling, sealing and leakage prevention, rust and corrosion protection, as well as shock absorption and buffering. It is hailed as the "blood" of automobiles. Engine oil consists of two main components: base oil and additives. The base oil is the primary constituent of lubricating oil, determining its fundamental properties, while additives compensate for and enhance the shortcomings of the base oil's performance, imparting certain new characteristics. Additives are an essential part of lubricating oil.

1. Diesel Engine Oil

The selection of diesel engine lubricating oil quality grade is based on two main criteria. One is the combined mechanical and thermal load of the automobile engine, expressed by the intensification coefficient; the other is the severity of the engine's operating conditions.

For high-speed naturally aspirated and turbocharged four-stroke diesel engines produced after 1990, diesel engine oil of CF-4 grade or higher should be used. For high-speed four-stroke diesel engines introduced after 1998, to meet the requirements of engine technological improvements and emission regulations, diesel engine oil of CH-4 grade or higher should be used. The CH-4 grade can replace CF-4 and CD. For high-speed four-stroke naturally aspirated and turbocharged, heavy-duty diesel engines produced after 2002, due to the presence of exhaust gas recirculation systems, formulation regulations, and exhaust aftertreatment technology requirements, diesel engine oil of CI-4 grade or higher should be used, which can replace CH-4, CF-4, and CD.