What is the difference between SAE 30 and 40 engine oil?

[OJohn]

The main differences between SAE 30 and 40 engine oil are as follows: 1. Different fluidity. SAE 30 oil has better fluidity than SAE 40 oil, which can better reduce fuel consumption and dissipate heat from the engine faster. 2. Different stability. SAE 40 oil has better oil stability than SAE 30 oil under extremely high temperature conditions of the engine. 3. Noise level. For older vehicles, using SAE 30 oil may result in slightly louder engine noise compared to using SAE 40 oil. Additional information: 1. Engine oil, also known as engine lubricant. It serves multiple functions for the engine including lubrication and friction reduction, auxiliary cooling, sealing and leak prevention, rust and corrosion protection, as well as shock absorption. 2. Engine oil consists of two components: base oil and additives. The base oil is the main component of lubricating oil, determining its fundamental properties. Additives can compensate for and improve the shortcomings of base oil performance, while also providing certain new characteristics, making them an important part of lubricating oil.