What does 10w/40 written on the front of the engine oil mean?
2 Answers
The 10W-40 marked on the bottle represents the viscosity grade of the lubricating oil product (indicating better fluidity at low temperatures and better viscosity at high temperatures). For detailed information, please see below: 1. The American Petroleum Institute classifies engine oils into different grades based on their quality levels: This standard uses the letter "S" to represent gasoline engine oils, and different grades are arranged in alphabetical order after the letter "S", such as SE, SF, SG, SH, SJ. The letters following "S" indicate higher oil grades as they appear later in the alphabet. 2. Classification of oil quality by viscosity grade: (1) The first category is single-grade viscosity, which is further divided into high-temperature and low-temperature types. (2) The second category is multi-grade viscosity all-weather type: Oil grades include SAE5W-30, SAE15W-40, SAE20W-50. The first part before the hyphen in this grade indicates the oil's low-temperature viscosity performance in winter, and the second part after the hyphen indicates its high-temperature viscosity performance in summer.
As an auto mechanic with a decade of experience in oil specifications, I can explain that the 'W' in 10W/40 stands for Winter. The 10W indicates the low-temperature viscosity grade - the lower this number, the better it performs in cold starts, with this grade suitable for winter temperatures as low as -25°C. The 40 represents high-temperature viscosity - higher numbers mean thicker oil films at high temperatures, providing effective engine protection during summer highway driving. This combination signifies an all-season motor oil suitable for most temperate climate variations. Always consult your owner's manual when selecting oil - using the wrong viscosity can increase fuel consumption or cause engine wear (for instance, older vehicles requiring high-mileage oil shouldn't use alternatives). These grades are defined by SAE standards, and regularly checking your oil condition is more crucial than anything - don't wait until engine knocking occurs to take action.
