What does SJ15W40 engine oil mean?

[OGenevieve]

SJ is the grade designation of the engine oil, and 15W40 represents the viscosity rating of the oil. Here, 15 indicates the lowest winter operating temperature of -20°C. The smaller the number before the 'W', the lower the low-temperature viscosity, the better the low-temperature fluidity, and the lower the applicable minimum temperature. Meanwhile, 40 represents the high-temperature viscosity, meaning the higher the number after the 'W', the higher the applicable maximum temperature. Additional notes on adding engine oil: 1. Higher viscosity does not necessarily mean better engine protection: High-viscosity oil not only adversely affects overall fuel consumption but also fails to protect the engine effectively. Another function of engine oil is cooling and heat dissipation. Blindly using high-viscosity oil will inevitably weaken the engine oil's heat dissipation performance. 2. Engine oils should not be mixed: The additive components in oils from different manufacturers are entirely different. The chemical compositions of these additives vary not only between brands but can also differ significantly within the same brand's different product lines. Mixing two brands of engine oil can cause chemical reactions under the engine's high temperatures, such as the formation of flocculants in the oil or an increase in viscosity.