1, Lubrication performance: 5W30 has low viscosity and good fluidity, and can lubricate and dissipate heat faster. The high viscosity of 5W40 can not form a stable oil film on the surface of engine parts, which leads to increased friction and wear, thus affecting the life and performance of the engine.

2. Cleanliness: 5w30 engine oil disperses lead compounds causing carbon deposition in the fuel into small particles through the action of its dispersant, and filters them out with the engine, thus cleaning the engine. 5W40 will produce sludge and block the oil circuit, resulting in poor lubrication and aggravating engine wear. So 5W30 is good.