What is the difference between 5W-30 and 10W-40?
3 Answers
The differences between 5W-30 and 10W-40 are as follows: 1. Different viscosity. The number after the letter W indicates the viscosity characteristics of the oil at high temperatures. 10W-40 oil has a higher viscosity than 5W-30. High-viscosity oil may be more suitable for high-speed driving or heavy-duty vehicles. 2. Different low-temperature fluidity. Oil starting with 5W has better low-temperature fluidity and can be used in colder regions. Oil starting with 5W can handle environments above -30 degrees Celsius, while 10W can only be used above -25 degrees Celsius.
I've been driving old cars for over a decade and have plenty of experience with oil changes. The main differences between 5W-30 and 10W-40 lie in cold-start performance and high-temperature behavior. During winter cold starts, 5W-30 flows much faster, quickly lubricating all engine components and reducing wear noise. In summer when driving long distances in high temperatures, 10W-40's thicker oil film provides better engine protection against overheating damage. However, 10W-40 has weaker low-temperature performance, feeling sluggish during cold starts. Regarding fuel consumption, the thinner 5W-30 typically saves fuel, while the more viscous 10W-40 consumes slightly more. Choose based on season and region - I recommend 5W-30 for cold northern areas, and 10W-40 for warmer regions or frequent high-temperature driving. Never use the wrong oil as it wastes money and damages your engine.
The engine oil numbering system is actually quite easy to understand. The 5W in 5W-30 represents low-temperature viscosity, with a smaller number indicating smoother flow in cold temperatures. The 10W in 10W-40 flows slightly slower, but the 40 indicates higher high-temperature viscosity, providing better protection by maintaining thickness in hot conditions. In short, 5W-30 offers superior low-temperature performance but lacks high-temperature protection, while 10W-40 is the opposite—strong in high temperatures but weaker in cold. They suit different climates: temperate regions may opt for medium viscosity like 15W-40 as a compromise. Additionally, vehicle type matters—newer compact engines often use 5W-30 for fuel efficiency, while older machines rely on 10W-40 to fill gaps and maintain seals. Just check the user manual instead of guessing blindly.
