What does SJ15W40 engine oil mean?
4 Answers
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.
I've been driving for over a decade and always pay attention to oil specifications when changing engine oil. In SJ 15W-40, 'SJ' is an API standard representing the oil's protection level, such as anti-wear capability and cleanliness, but it's a relatively old specification, not as efficient and energy-saving as the newer SP grade. The '15W-40' indicates the oil's viscosity characteristics: 15W means good fluidity during cold starts, capable of flowing smoothly at around -15 degrees Celsius; 40 represents medium viscosity at high temperatures, providing stable protection during high-speed engine operation. It works decently in my older car model, reducing engine noise and extending engine life. However, modern engines demand higher specifications, so newer grades might be more suitable. Using this oil long-term in newer cars could lead to higher fuel consumption. Always choose engine oil based on your vehicle's manual recommendations—don't compromise quality for price, or you might face expensive engine repairs later.
When working in the garage, I often get asked about motor oil ratings. In SJ 15W-40, 'SJ' refers to the API service category, specifically designed for gasoline engines. It provides basic carbon deposit and friction protection, but compared to newer ratings, its oxidation resistance is weaker, making it potentially more suitable for vehicles from the 1990s. 15W-40 is the viscosity rating: the 15W's low-temperature performance ensures easy cold starts in winter, while the 40 indicates higher viscosity at high temperatures for better protection, ideal for regions with significant seasonal temperature variations. Many mid-sized cars can use this oil without issues, as long as the viscosity matches the temperature environment. I must remind you, if the engine frequently overheats or fuel consumption suddenly increases, check if the oil has been mixed or expired, as this could lead to internal component damage. Regular oil changes are crucial.
Hey, I'm a regular car owner who does my own vehicle maintenance. The term SJ 15W-40 oil means that SJ represents a quality grade, ensuring basic cleanliness and protection, while 15W-40 indicates viscosity numbers: 15W means quick cold-weather starts with less risk of seizing, and 40 means thicker oil in hot weather to protect the engine. This type of oil is quite versatile, and my family's SUV has been using it for three years without any issues. However, it's important to note that newer fuel-efficient cars might not be compatible with older grades like SJ. It's best to refer to the manual to choose the right viscosity oil to avoid premature wear. Also, don't delay oil change intervals too much—engine longevity depends on it.
