What is the difference between 5w40 and 0w40 engine oil?

[NaomiLynn]

5w40 and 0w40 engine oils differ in their low-temperature flow performance: 5w40 oil can flow normally at temperatures as low as -30°C, while 0w40 oil can flow normally at temperatures as low as -35°C. The functions of engine oil are: 1. To reduce friction and high temperatures; 2. To minimize gas leakage and prevent external contaminants; 3. To prevent contact between water, air, acidic harmful gases, and engine components; 4. To cushion the pressure rise in the engine cylinder ports; 5. To clean dirt generated on the working surfaces of components. Engine oil consists of base oil and additives. Base oils are categorized by quality into Group I, Group II, and Group III base oils, with Group I and II being mineral oils and Group III being synthetic base oils. There are various types of additives, and the quantity and quality of additives directly affect the API quality rating of the lubricant.