What's the Difference Between 5W30 and 5W40 Engine Oil?

[DiEva]

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.

[AthenaFitz]

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.

[SanSavannah]

Regarding these two types of engine oil, simply put, 5W-40 is thicker at high temperatures, making it more suitable for high-load driving. They perform the same in low temperatures, but the 40-grade oil is less prone to thinning at higher engine temperatures, offering better protection, especially during long-distance driving at high speeds or in hot regions. The downside is it might slightly increase fuel consumption. The 30-grade oil is thinner, more fuel-efficient, and smoother for daily commuting, but it may not withstand the wear and tear of aggressive driving, such as mountain road climbs. My suggestion is to choose based on your car's age: use 30 for newer engines and switch to 40 for older cars for added security. A related tip: don’t just focus on the oil grade; the brand and quality of the oil matter too, with synthetic oils being more durable than mineral oils. If you drive aggressively, consider changing the oil more frequently to avoid engine issues.

[Miriam]

The difference between 5W30 and 5W40 engine oil lies in their high-temperature viscosity. The 5W part is the same, meaning they perform identically during cold starts. However, the 40 grade is thicker when the engine is hot, providing better protection, making it suitable for aggressive driving or hot climates. The 30 grade is thinner, offering better fuel efficiency and smoother operation. Beginners shouldn't worry—just follow the owner's manual recommendations and avoid switching grades arbitrarily.