Engine oil is in front of 5W30, generally there will be an S/L, S/M, S/N, S stands for gasoline, L, M, N, the later the better.
5, generally refers to the temperature, refers to the working range of low temperature, and 5 refers to-15℃.
30, 40, generally refers to the viscosity of engine oil. In general, the thicker the oil, the better the protection for the engine. However, it doesn't mean that 30 or 20 oil is bad for the engine.
Note that if you don't drive a violent car, or a racing car, or a * * * performance car, the speed can easily be lowered to 6000-7000 rpm, generally 30 is enough, enough. Moreover, the thicker the engine oil, the more fuel is consumed, and the thinner the engine oil is, which saves fuel. At the same time, the viscosity of engine oil also has an effect on engine mute (the difference is not big, and the time can be ignored).