What is the difference between 20W50 and 15W40?

[Bentley]

15W40 and 20W50 are two different grades of engine oil with different low-temperature fluidity and high-temperature viscosity. The specific differences are as follows: Difference in low-temperature fluidity: The smaller the number, the better the low-temperature fluidity and cold-start performance. 15W40 has better low-temperature fluidity than 20W50 and can withstand lower temperatures. 15W40 can withstand temperatures as low as -20°C, while 20W50 can withstand temperatures as low as -15°C. Therefore, 15W40 offers better cold-start performance. Difference in high-temperature viscosity: The larger the number, the higher the viscosity and the better the high-temperature protection. 20W50 has higher high-temperature viscosity than 15W40, providing better cooling and lubrication at high temperatures, resulting in quieter engine operation. However, it has poorer fluidity and greater resistance, which also increases fuel consumption.