What's the Difference Between 5W30 and 5W40 Engine Oil?
2 Answers
The difference between 5W30 and 5W40 engine oils lies in their viscosity: 5W30 oil has a viscosity index of 30 at 100 degrees Celsius, while 5W40 oil has a viscosity index of 40 at the same temperature. In 5W30 oil, the number 5 indicates that the oil is suitable for temperatures above -25 degrees Celsius, and the 'W' stands for winter. The smaller the number before the 'W', the better the low-temperature fluidity. The functions of engine oil are: 1. To reduce friction and high temperatures; 2. To minimize gas leakage and prevent contamination from external pollutants; 3. To protect against contact with water, air, acidic harmful gases, and parts; 4. To cushion the pressure rise in the engine cylinder port; 5. To clean dirt generated on the working surfaces of parts.
I often get asked this question. The main difference between these two types of motor oil lies in their viscosity at high temperatures. The 5W in both 5W-30 and 5W-40 is the same, indicating similar fluidity in cold winter conditions, making engine starts easier. However, the 30 and 40 are different: 5W-40 is thicker than 5W-30 when the engine is running hot, like a slightly thicker sauce, providing better protection against wear on engine components, especially during long-distance driving or in hot weather. That said, thicker oil may slightly increase fuel consumption and make the car feel a bit heavier during acceleration. On the other hand, 5W-30 is thinner, more fuel-efficient, and offers smoother driving, but it may not provide sufficient protection for older engines or under aggressive driving conditions. Which one to choose depends on your car's manual recommendation—generally, newer cars use 5W-30, while older ones use 5W-40. Never switch randomly! Regular oil changes can extend your engine's lifespan, and remember to check if the viscosity is appropriate when the seasons get warmer for safe and worry-free driving.
