What is SAE 10W-40 engine oil?
1 Answers
SAE 10W-40 is a fully synthetic engine oil, where SAE stands for the viscosity grade designation of the oil and is the abbreviation for the Society of Automotive Engineers. The "W" stands for Winter, and 10W indicates resistance to external low temperatures of -25°C. The smaller the number before the W, the better the oil's low-temperature fluidity, meaning it can be used in lower environmental temperatures and provides better engine protection during cold starts. The number after the W represents the oil's kinematic viscosity at 100°C, with 40 being the indicator of the oil's high-temperature resistance. Therefore, this is just one type of engine oil, and higher numbers indicate higher viscosity. Engine oil (Engine-oil) is the lubricant used by engines. It consists of base oil and additives. The density of engine oil is approximately 0.91×103 (kg/m3), and it serves functions such as lubrication and wear reduction, auxiliary cooling, sealing and leak prevention, rust and corrosion prevention, and shock absorption. It is often referred to as the "blood" of a car. Engine oils are classified as follows: Mineral oil: A commonly used lubricant on the market, it is derived from the distillation of petroleum to extract useful substances like gasoline and aviation fuel, followed by further processing of the remaining base oil. Semi-synthetic oil: Made from semi-synthetic base oil, it is a product refined from mineral oil through hydrocracking technology. It is a mixture of mineral oil and fully synthetic oil in a 4:6 ratio. Semi-synthetic oil's purity is very close to that of fully synthetic oil, but its cost is slightly higher than mineral oil, making it an ideal transitional product from mineral oil to synthetic oil. Fully synthetic oil: The highest grade of engine oil, derived from ethylene and propylene dispersed from natural gas or crude oil, undergoes complex chemical reactions such as polymerization and catalysis to form a lubricating fluid composed of large molecules. Notes on selecting engine oil: The viscosity of engine oil changes with temperature, so special attention should be paid to its performance under low and high temperatures. For example, in 5W-30, the number before the W indicates low-temperature fluidity, with 5W representing the ability to withstand -30°C. The smaller this number, the better the low-temperature fluidity, ensuring smoother cold starts for the car. The number after the W represents the oil's kinematic viscosity at 100°C, with higher numbers indicating better ability to maintain viscosity at high temperatures, which can also be understood as better lubrication performance under high temperatures. Engine oil should be selected based on the engine's requirements. It is unnecessary to use overly advanced oil in engines with lower requirements, nor should lower-grade oil be used in engines with higher requirements. Multi-grade oils are preferred due to their cost-effectiveness, long lifespan, and high efficiency, providing better protection for the engine. Based on the characteristics of multi-grade oils, they may appear darker prematurely and have lower oil pressure compared to conventional oils, both of which are normal phenomena.
