Is SAE5w40 a Fully Synthetic Engine Oil?

1 Answers
LeDaniel
07/30/25 6:24am
SAE5w40 is a semi-synthetic engine oil. SAE stands for the Society of Automotive Engineers, representing the viscosity index of the oil. The 'W' is an abbreviation for Winter, and the number before 'W' indicates the low-temperature viscosity—the smaller the number, the lower the viscosity and the better the low-temperature fluidity. The number after 'W' represents the high-temperature viscosity—the larger the number, the higher the viscosity. Below are methods for selecting engine oil: Choosing Based on Oil Grade: API standard classification starts with 'S,' followed by letters E, F, G, H, G, L, M, N. The further back the letter, the higher the quality grade and the better the performance. Choosing Based on Oil Viscosity: Generally, subtracting 35 from the number before 'W' gives the minimum operating temperature of the lubricant. Low-temperature viscosity grades are 0W, 5W, 10W, 15W, 20W, 25W—the smaller the number, the better the low-temperature performance. The '-30' number indicates the viscosity at 100 degrees Celsius, typically categorized as 20, 30, 40, 50, 60—the larger the number, the higher the viscosity.
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