Which oil is best for 5W-30 or 5w40?
There isn’t a universal “best” oil; the right choice depends on your vehicle’s requirements, climate, and driving style. Most modern engines call for 5W-30, which offers good fuel economy, but some engines and hot conditions benefit from 5W-40.
Ultimately, the decision between 5W-30 and 5W-40 centers on the engine maker’s specifications, operating temperature, and your climate. This article explains how to decide which grade to use and what other factors matter for protection and longevity.
When to choose 5W-30
5W-30 is a versatile, widely prescribed grade that balances cold-start performance, protection, and efficiency in a broad range of modern engines. Use 5W-30 when the manual or OEM permits it and you want better fuel economy or easier cold starts in temperate climates.
- Manufacturer specification: Follow the owner's manual or OEM bulletins that specify 5W-30 (or an approved equivalent).
- Fuel economy and emissions: 5W-30 typically yields lower friction at cold start and can improve efficiency in many engines.
- Cold-start performance: Suitable for moderate and cold climates, providing adequate lubrication on startup.
- Engine design and durability: Commonly recommended for many modern gasoline engines and some diesel engines that specify this grade.
The main takeaway is to prioritize the OEM spec and select 5W-30 when it is listed as the approved viscosity, especially for efficiency-driven designs.
When to choose 5W-40
5W-40 is a thicker-at-temperature option that can provide more robust protection in hot conditions or high-load situations. It’s worth considering when the manufacturer calls for it or when you operate under conditions that stress the engine (high temps, towing, or performance variants).
- High-temperature or heavy-load operation: Hot climates or engines under sustained high load can benefit from a thicker oil film at operating temperature.
- Manufacturer specification: Some engines explicitly require 5W-40 to meet OEM performance specs or warranty requirements.
- Turbocharged or performance engines: Boosted engines may need 5W-40 to maintain stable lubrication under boost and higher RPMs.
- Older or high-mileage engines: In certain cases, 5W-40 can help with wear protection, provided the spec allows it.
Concluding for List B: Use 5W-40 when the manufacturer specifies it or when your driving profile and climate justify a thicker-at-temperature oil for protection and reliability.
Other considerations
In addition to viscosity, ensure the oil meets the required API/ILSAC grades and OEM approvals. For many modern vehicles, synthetic or full-synthetic blends offer better protection and longer drain intervals. The correct specification often includes viscosity, API service category, and manufacturer approvals (e.g., MB 229.5/229.51, VW 502 00, BMW LL-01, etc.).
Practical recommendations
Key steps to choose the right oil:
- Always consult the owner’s manual or dealer for the exact grade and spec.
- Choose synthetic or semi-synthetic oil if your manual allows it, especially for high-temperature or turbocharged engines.
- Do not mix grades or switch grades outside the manufacturer’s approved options, and adjust drain intervals accordingly.
- Consider climate and driving: colder climates favor grades with better cold flow; hot climates can tolerate thicker oils if approved.
In short, the best oil for any given vehicle is the one that matches the OEM specification for viscosity, performance, and approvals, with 5W-30 being a common default and 5W-40 used in hotter or high-load contexts.
Summary: The decision between 5W-30 and 5W-40 hinges on the carmaker’s specification, engine design, and operating conditions. Use 5W-30 if the manual specifies it and you want efficient cold starts and fuel economy; opt for 5W-40 if the manual requires it or you routinely operate in hot climates, under heavy loads, or with higher-performance engines. Always check OEM approvals and conduct regular oil changes.
When should you use 5w40 oil?
5w40 is better for starting your engine at low temperatures as it flows more easily at these temperatures. When the engine is running and hot, 5w40 and 10w40 have high viscosities and are equally effective in protecting against engine wear.
Is 5w-30 or 5w-40 better for hot weather?
In practice, this means that each oil is just as viscous at lower temperatures and will remain viscous at -30°C, however 5w40 oil outperforms 5w30 oils at higher temperatures, being effective up to ambient temperatures of 50°C, as opposed to 30°C.
Which is better engine oil, 5w30 or 5w40?
5w30 vs 5w40: oil characteristics
5w30 is ideal for operating temperatures ranging from -25°C to 25°C, while 5w40 extends its range slightly to -25°C to 35°C. This means that if you're driving in colder climates, 5w40 might offer better performance due to its ability to withstand lower temperatures.
What will happen if I use 5w40 instead of 5w30?
Putting 5W-40 instead of 5W-30 will result in slightly decreased fuel efficiency and potential performance issues, but is unlikely to cause major damage, especially in warmer climates or for older engines. The main difference is that 5W-40 oil is thicker at operating temperature, which can slightly increase friction and oil pressure. It's always best to follow the manufacturer's recommendation, which is found in your owner's manual or on the oil fill cap.
What to expect
- Slightly reduced fuel economy: Thicker oil creates more drag on engine components, leading to a small decrease in fuel efficiency.
- Potential performance impact: A thicker oil may slightly reduce high-end horsepower.
- Increased oil pressure: 5W-40 has higher viscosity, which can lead to higher oil pressure readings.
- Potential benefit for older engines: A thicker oil may be beneficial for older, high-mileage engines that have increased wear and tear, as it can help maintain oil pressure.
- No harm in cold starts: The "5W" rating is the same for both oils, meaning both will have similar flow characteristics during cold starts.
When to be cautious
- Modern engines: Modern engines are designed with precise tolerances, and using a thicker oil can cause problems that the manufacturer did not design for, so it is best to stick with the recommended 5W-30.
- Warranty issues: Using an oil that does not meet the manufacturer's specifications can potentially void your warranty.
- Stop-and-go traffic: If your engine runs hot in stop-and-go traffic, the thicker oil could be a benefit.
Best practices
- Check your owner's manual: The manufacturer's recommendation is the safest guide. Check the manual for the correct oil viscosity and specifications.
- Don't switch for "just because": There's no need to switch from 5W-30 to 5W-40 unless you have a specific reason, such as a high-mileage engine or a preference for heavier oil in a hot climate.
- Stick to a single type: If you do switch, make sure to use the new oil at your next oil change, as mixing different viscosities is not ideal.
