What does 5w40 mean for engine oil?
2 Answers
Engine oil 5w40 is a type of engine oil grade. 5W represents resistance to external low temperatures of -30°C, and 40 indicates that the kinematic viscosity standard at 100°C is between 12.5mm²/s and 16.3mm²/s. Meaning of engine oil grades: Engine oil grades consist of two parts: classification and viscosity specification. W stands for winter, and the smaller the number before it, the better the low-temperature fluidity of the oil, indicating a lower usable environmental temperature and better protection for the engine during cold starts. The number after W is an indicator of the oil's high-temperature resistance, with higher values indicating better protection performance at high temperatures. Classification of automotive engine oils: Automotive engine oils are specifically classified into 4 types for summer use, 6 types for winter use, and 16 types for all-season use. Summer oil grades include 20, 30, 40, and 50. Winter oil grades include 0W, 5W, 10W, 15W, 20W, and 25W. All-season oil grades include 5W-20, 5W-30, 5W-40, 5W-50, 10W-20, 10W-30, 10W-40, 10W-50, 15W-20, 15W-30, 15W-40, 15W-50, 20W-20, 20W-30, 20W-40, and 20W-50.
The oil grade 5W-40 is part of the SAE viscosity grading system. The 'W' stands for winter, and the preceding number '5' indicates the oil's low-temperature fluidity, meaning it remains less viscous at around -25°C, making the engine easier to start. The following number '40' indicates moderate viscosity at high temperatures, ensuring lubrication protection during high-temperature engine operation. This multi-grade oil is suitable for year-round use, avoiding issues like the oil being too thin in summer or too thick in winter. Choosing the wrong oil grade, such as using a single-grade oil or one with higher low-temperature specifications, may lead to difficulties in starting, increased fuel consumption, or accelerated engine wear. It is recommended to regularly check the dipstick and refer to the vehicle manual to select the appropriate oil grade.
