What does 15w40 and 20w50 mean for diesel engine oil?

1 Answers
DeJackson
07/29/25 4:16pm
15W40 and 20W50 are two different grades of engine oil, both belonging to multi-grade oils. The following are the differences between the two: 1. Different low-temperature fluidity (the smaller the number, the better the low-temperature fluidity and the better the low-temperature starting performance). The low-temperature fluidity of 15W40 is better than that of 20W50, and it can withstand lower temperatures. 15W40 can withstand a minimum temperature of -20°C, while 20W50 can withstand a minimum temperature of -15°C. Therefore, 15W40 has better low-temperature starting performance. 2. Different high-temperature viscosity (the larger the number, the higher the viscosity and the better the high-temperature protection performance). The high-temperature viscosity of 20W50 is higher than that of 15W40, providing better cooling and lubrication at high temperatures, resulting in quieter engine operation. However, its fluidity is poorer, and the resistance is greater, which also increases fuel consumption.
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