What is the Difference Between 10W30 and 10W40?

[AriannaMarie]

The differences between 10W30 and 10W40: 10W30 and 10W40 share the same low-temperature fluidity, maintaining normal viscosity at temperatures above -25°C, ensuring the vehicle operates normally. The engine can function properly. However, their high-temperature viscosities differ. 10W30 has lower high-temperature viscosity, better fluidity, and can reduce fuel consumption. The engine dissipates heat faster, but after application, the engine noise tends to be slightly louder. 10W40 has higher high-temperature viscosity, is thicker, and after application, the engine can handle higher loads with less noise, smoother operation, and greater stability. However, its fluidity is poorer, creating higher resistance for internal engine components and consuming more fuel. Comparison of 10W30 and 10W40 performance: Relatively speaking, the lower viscosity and better fluidity of 10W30 provide stronger power compared to 10W40, which has some disadvantages. Although 10W30 is more fuel-efficient and offers stronger power, its high-temperature shear resistance is weaker, and the oil film is prone to breaking, leading to higher wear than the higher-viscosity 10W40. Although 10W40 has poorer fluidity, higher resistance, and consumes more fuel, its performance is more stable, ensuring the engine operates normally under high-temperature conditions. Japanese naturally aspirated engines are more suitable for low-viscosity 10W30 oil, while German turbocharged engines are better suited for high-viscosity 10W40 oil. Choosing engine oil should not only consider power but also require comprehensive evaluation to select the most suitable oil for your engine.

[LucyLee]

Both 10W30 and 10W40 are multi-grade engine oils suitable for all seasons, with the key difference lying in their high-temperature viscosity. Simply put, the higher the number after the 'W,' the thicker the oil film at high temperatures. 10W40 provides stronger protection than 10W30 when the engine is under heavy load, especially during long summer trips or frequent hill climbing. However, 10W30 offers slightly better fluidity, enabling faster cold starts and better fuel efficiency, making it ideal for daily urban commuting. The choice depends on your driving conditions. For instance, in southern regions where summer temperatures often reach 40°C, or for older vehicles with over 80,000 kilometers, 10W40 is a safer bet. But for newer cars driven in northern areas, 10W30 is sufficient. Also, always check the maintenance manual—some vehicles explicitly require 10W30 oil, and using 10W40 might negatively impact performance.

[DiLilah]

These two engine oils can be used in both winter and summer, but their suitable temperature ranges differ. While their performance during cold starts is similar (the '10' before the W indicates usability down to -25°C), the difference becomes apparent once the engine warms up. The 10W30 is thinner at 100°C, making it suitable for gentle driving; whereas the 10W40 is thicker at high temperatures, preventing the oil film from breaking easily during high RPMs. If you frequently drive fully loaded on highways or prefer a sporty driving style, the 40 variant offers better engine protection. However, higher viscosity also means slightly increased fuel consumption, roughly 0.5-1 liter more per 100 km. A friend who worked at an auto repair shop mentioned that German cars generally perform better with 40-grade oil, while Japanese cars mostly use 30-grade. When changing oil, remember to check the ACEA certification mark on the container to avoid buying the wrong one.

[VonAlexis]

The most obvious difference is the high-temperature viscosity numbers, where 30 and 40 represent the kinematic viscosity at 100°C. A 40-weight oil is less prone to thinning when the engine overheats, making it especially friendly for high-mileage vehicles. My decade-old classic car would burn a slight amount of oil when using 30-weight, but switching to 40-weight solved the issue. However, never blindly use high-viscosity oil in new cars—modern engines have tighter tolerances, and using 40-weight can actually increase resistance. Additionally, there's almost no difference in performance between the two at -20°C in winter. When choosing oil, consider your driving habits: use 30-weight for daily city traffic jams, and opt for 40-weight if you frequently haul loads or drive on construction sites. Remember, full synthetic oils offer a wider performance range than mineral oils, providing better protection at the same viscosity grade.

[Rogers]

10W40 provides better high-temperature protection than 10W30 but with slightly higher fuel consumption. The key lies in oil film thickness: 40-grade oil maintains stable lubrication under extreme engine conditions (e.g., continuous 4000 RPM hill climbing), reducing metal friction. Meanwhile, 30-grade oil flows more easily, reaching lubrication points faster during cold starts. If you're in hot regions like Hainan or drive turbocharged vehicles, 40-grade is recommended. For Northeast China with mainly short-distance commuting, 30-grade suffices. A common misconception is that higher viscosity oil is always better, but modern engines actually favor lower viscosity. Last year's test on identical vehicles showed 30-grade oil saved 0.8L gasoline per 100km.