What is 5W-40 oil used for?

5W-40 engine oil is a multigrade lubricant used in many gasoline and diesel engines to provide good cold-start flow and strong high-temperature protection.

In addition to its dual-temperature characteristics (5W at cold start and 40 at operating temperature), 5W-40 can be synthetic or synthetic-blend and is commonly recommended for engines that experience a wide range of temperatures or high-performance operation. It is widely used in European vehicles and in various regions where OEMs specify a 5W-40 viscosity.

Applications and suitability

The following summary highlights typical situations where 5W-40 is commonly chosen or required.

• Passenger cars with gasoline engines that specify 5W-40 in the owner's manual.


• Diesel engines, including modern turbocharged or common-rail designs, that call for 5W-40 or a similar high-temperature viscosity oil.


• Turbocharged or high-performance engines that need strong protection during high engine speeds and temperatures.


• Vehicles operating in a broad temperature range, including cold climates where easy cold-start lubrication is important.

When selecting oil, always verify the OEM specification, as some engines may require a different viscosity or a different multi-grade (for example, 0W-40 or 5W-30) depending on model year and climate.

Identifying the right 5W-40 on the bottle

Look for the following indicators on motor oil labels to ensure compatibility with your engine:

• Viscosity grade: 5W-40 (the primary rating you need to match).


• API service category: a current API rating such as SN/SN Plus or newer.


• ACEA rating or OEM approvals: many 5W-40 oils carry ACEA A3/B4 and/or OEM approvals, depending on the formulation.


• Oil type: synthetic, synthetic-blend, or mineral; synthetic or semi-synthetic oils are common for 5W-40 applications.


• Manufacturer notes on usage: climate and engine notes; some engines require full synthetic for long drain intervals, others accept blends.

Note: Always check the bottle and your owner’s manual for the exact requirements for your vehicle; using the wrong specification can impact protection, emissions, and warranty coverage.

Choosing the right oil for your engine

To select the best oil, consider the following steps:

1. Consult the vehicle's owner manual to confirm the recommended viscosity and any OEM approvals.


2. Assess your climate and driving style; cold climates and frequent short trips may benefit from one oil, while hot climates and prolonged highway driving may favor another.


3. Evaluate engine type and condition, including turbochargers, direct injection, and high-performance designs that may require more robust protection.


4. Check for OEM approvals (such as manufacturer-specific specifications) on the oil label and confirm compatibility with your engine.


5. Decide between synthetic, synthetic-blend, or mineral options based on maintenance schedule, budget, and warranty considerations.


6. Follow recommended drain intervals and use the correct fill quantity; if in doubt, consult a qualified technician or the dealer.

In short, 5W-40 is a versatile and widely used oil grade that suits many engines when the manufacturer specifies it and that climate and driving conditions demand a broad temperature range.

Summary

5W-40 engine oil provides versatile lubrication for a wide range of gasoline and diesel engines, delivering good cold-start flow and robust protection at operating temperature. Its use is most common where OEMs specify a multi-grade 5W-40 or where engines demand a blend that performs well across cold and hot conditions. Always follow the vehicle’s manual and look for the appropriate OEM approvals on the oil container.

What happens if I put 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. 

What cars can you use 5w40 oil for?

Fully Synthetic Oil 5W-40 – Mercedes-Benz, VW, Renault, Porsche. Redex 5W-40 is a fully synthetic motor oil that's suitable for use in a range of engines, including Mercedes-Benz, VW, Renault, and Porsche models.

What is 5W-40 oil best for?

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.

Which is better 5w30 or 5w40?

Neither 5w30 nor 5w40 is universally "better"; the right choice depends on your vehicle and climate. 5w30 is better for cold weather and fuel efficiency because it flows more easily when cold, while 5w40 is better for hot climates and demanding conditions like towing or high performance, as it provides a thicker protective film at high temperatures. Always check your vehicle's owner's manual to determine the manufacturer's recommendation, as it is the most important factor. 
This video explains the key differences between 5W30 and 5W40 engine oils: 52sHonest Mechanic ColoradoYouTube · Jan 13, 2024
Choose 5w30 if:

• You live in a colder climate: Its lower viscosity at operating temperature allows for faster lubrication and easier engine startups in cold weather. 
• Fuel efficiency is a priority: 5w30 causes less drag and can lead to better gas mileage. 
• Your engine is a modern gasoline engine: It's the recommended oil for many modern gasoline applications. 

Choose 5w40 if:

• You live in a hot climate: The thicker oil provides better protection under high heat conditions. 
• You frequently tow or carry heavy loads: The thicker oil offers better protection for high-stress situations. 
• You have a high-performance or high-mileage engine: 5w40 can provide better protection and help maintain oil pressure in older or more demanding engines. 
• Your vehicle is a diesel: 5w40 is the suggested oil for most diesel applications. 

This video demonstrates the performance difference between 5W30 and 5W40 engine oil in a diesel engine under heavy load: 1mThe Auto BrainsYouTube · Oct 27, 2025
The bottom line

• Consult your owner's manual: The manufacturer's recommendation is the most crucial factor to consider. 
• Consider your climate: Choose 5w30 for cold climates and 5w40 for hot climates. 
• Consider your driving habits: 5w40 is better for demanding use, while 5w30 is generally suitable for average use and prioritizing fuel economy.