What is the difference between engine oil 30 and 40?

[Jonah]

Here are the differences between oil 30 and oil 40: 1. Oil 30 has better fluidity than oil 40, which can further reduce fuel consumption and dissipate heat from the engine more quickly. 2. For older vehicles, using oil 30 may result in slightly louder engine noise compared to oil 40. 3. Oil 40 has better oil stability than oil 30 under extremely high-temperature conditions in the engine. Additional information: Characteristics of oil grades: 1. SAE grade, also known as viscosity grade, is represented as **W**. The W stands for winter. The smaller the number before the W, the lower the viscosity at low temperatures, the better the low-temperature fluidity, and the lower the applicable minimum temperature. During normal use, the resistance is smaller, which helps reduce fuel consumption. 2. The larger the number before the W, the higher the viscosity at low temperatures, the worse the low-temperature fluidity, and it cannot be used below temperatures beyond its capability; otherwise, the engine may fail to start.