What does 10w-40 mean in engine oil?

1 Answers
Jenna
07/29/25 9:45pm
10W40 in engine oil represents the viscosity of the oil. 10W-40 is a specification indicating the viscosity grade. The '10w' indicates that the minimum temperature this oil can be used in is -25 degrees Celsius, where 'w' stands for winter, and the number before 'w' represents the oil's low-temperature fluidity. The smaller the number, the better the oil's fluidity at low temperatures. The number after 'W' represents the oil's viscosity at 100 degrees Celsius. Contrary to the number before 'W', a higher value here means better protection for the engine. Regions that typically meet the usage conditions for 10W40 oil include North China and the central-western parts of the country. Engine oil must have a certain viscosity to ensure that moving parts have an oil film at various operating temperatures, effectively preventing wear between the contact surfaces of moving parts inside the vehicle and reducing damage to car components. However, the viscosity of the oil does not affect engine startup, nor does it mean that higher viscosity is always better. On the contrary, excessive oil viscosity can lead to increased wear on certain parts.
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