The difference between engine oil 5w40 and 5w30:

1. The numbers 40 and 30 after 5w represent the viscosity. The larger the number, the greater the viscosity, and the higher the applicable maximum temperature. In other words, 5w40 can adapt to higher temperature environments than 5w30, and high-viscosity engine oil (with a higher value) may also be more suitable for high-speed or heavily loaded vehicles.

2. But both start with 5w, which means that the lowest temperature they can withstand is the same. The smaller the number before W, the smaller the low-temperature viscosity and the better the low-temperature fluidity. It is suitable for The lower the minimum temperature; using oil with a lower value in front of W will make it easier to start the engine in cold weather. So which one is better mainly depends on the driving environment of the vehicle. If it is a hot area like Hainan in China, it is better to use 5w40. If not, it will be better to use 5w30.