What is the difference between 5W-30 and 5W-40 engine oil?
2 Answers
5W-30 and 5W-40 engine oils mainly differ in the following aspects: 1. 5W-40 oil provides better protection for the engine under high-temperature conditions compared to 5W-30. 2. 5W-40 has slightly higher viscosity than 5W-30. Due to its greater viscosity, the resistance to crankshaft rotation increases, making 5W-40 less fuel-efficient. Additional information: 1. Both 5W-30 and 5W-40 are SAE standard viscosity grades for engine oil. The first number indicates the lowest temperature at which the oil can be used. 2. The second number represents the kinematic viscosity of the oil at 100°C. A higher number indicates greater viscosity, better protective performance under high temperatures, and improved stability in high-temperature conditions.
I've been driving for over a decade, and the difference between 5W-30 and 5W-40 motor oil mainly comes down to high-temperature performance. Both are labeled '5W' for the low-temperature part, meaning they have similar fluidity at around -25°C in winter, making the engine easier to start. The difference lies in the numbers '30' and '40': 5W-30 has lower viscosity when the engine heats up—it's thinner—making it suitable for cold regions or daily short-distance driving, which can help reduce fuel consumption. On the other hand, 5W-40 is thicker at high temperatures, with a more robust oil film, making it better for hot weather or long-distance highway driving, protecting the engine from high-temperature wear. Living near the boundary between northern and southern regions, I noticed that using 5W-40 in winter made the engine start slightly slower, but in summer, it felt more stable during high-speed driving. I recommend checking your car's manual or local temperatures when choosing—don’t just switch back and forth to save money, as it could affect engine longevity over time. Additionally, higher-viscosity oil might slightly increase fuel costs, but it reduces maintenance hassles in the long run.
