What is the difference between 5W-30 and 5W-40?

[McCayden]

The differences between 5W-30 and 5W-40: 1. Different kinematic viscosity: The kinematic viscosity of 5W-30 oil at 10°C is 30; the kinematic viscosity of 5W-40 oil at 10°C is 40. 2. Different oxidation resistance: 5W-30 oil has poorer oxidation resistance, providing weaker engine protection during startup; 5W-40 oil has better oxidation resistance, offering stronger engine protection during startup. 3. Different detergency: 5W-30 oil is more effective at inhibiting carbon deposits, varnish, and sludge formation or removing these deposits; 5W-40 oil is less effective at inhibiting carbon deposits, varnish, and sludge formation or removing these deposits. In practical applications, the difference between the two is not significant, as both 5W-30 and 5W-40 have a wide applicable temperature range and are all-season motor oils, providing both low-temperature startup fluidity and a thicker oil film at high temperatures for better engine protection.