Can I put 5W-40 oil instead of 5W-30?

Yes—if your owner’s manual lists 5W-40 as an approved grade for your engine and climate, you can use it; it will be thicker at operating temperature than 5W-30, which can slightly reduce fuel economy but may help in high-heat or high-load use. The key is to match the manufacturer’s required specifications (API/ACEA and any OEM approvals) and consider warranty, emissions systems, and driving conditions.

What changes when you go from 5W-30 to 5W-40

Both oils have the same winter rating (5W), so cold-start performance is broadly comparable. The difference is at operating temperature: 5W-40 is more viscous than 5W-30, typically providing a higher high-temperature high-shear (HTHS) viscosity. That can bolster film strength under heat and load, which some turbocharged or older engines benefit from. The trade-offs can include a modest hit to fuel economy and, in engines designed around lower-viscosity, lower-HTHS oils, potentially less optimal operation of tight-tolerance components.

When it’s okay—or even beneficial

These are scenarios where stepping up from 5W-30 to 5W-40 is commonly acceptable or advantageous, provided the oil meets your manufacturer’s approvals.

• Your manual lists both 5W-30 and 5W-40 on the temperature/viscosity chart.
• Hot climate, heavy loads, towing, spirited driving, or track use where oil temps run high.
• High-mileage engines that consume or burn 5W-30; the thicker 5W-40 may reduce consumption.
• European engines that specify high-HTHS oils (e.g., ACEA C3 or A3/B4) where 5W-40 is often the default.
• Turbocharged gasoline or diesel engines where the OEM explicitly approves 5W-40.

In these cases, 5W-40’s higher operating viscosity can enhance protection under stress without compromising cold starts, as long as it carries the correct specifications.

When you should not substitute 5W-40

There are also situations where switching from 5W-30 to 5W-40 is not recommended.

• Your vehicle requires a specific grade for fuel-economy or design reasons and does not approve 5W-40.
• Engines designed around lower-HTHS oils (many modern gasoline engines targeting efficiency) that expect 5W-30 meeting ILSAC/API “resource conserving” performance.
• Vehicles with diesel particulate filters (DPF) or gasoline particulate filters (GPF) that require low-SAPS oils where your chosen 5W-40 lacks the necessary ACEA C-class/OEM approvals.
• You are under warranty and the manufacturer does not list 5W-40 among approved grades.
• Extremely cold climates where a 0W-30/0W-40 is recommended for easier cranking below the 5W range.

Ignoring the OEM’s approved grades or emissions-system requirements risks warranty issues and, over time, can increase ash buildup in particulate filters if the oil chemistry isn’t correct.

Check the approvals, not just the numbers

Viscosity is only part of the story. Match the specification your manual calls for. For gasoline engines, API SP (current category) is typical; for fuel-economy–focused oils, ILSAC GF-6A/6B remains common in 2025, while newer ILSAC formulations are emerging. European specs are often ACEA C3 (low SAPS, HTHS ≥ 3.5) or A3/B4 (higher SAPS, HTHS ≥ 3.5). Many 5W-40 oils meet ACEA C3 or A3/B4 and carry OEM approvals like Mercedes-Benz 229.5/229.51/229.52, BMW Longlife-01, Porsche A40, or VW 502 00/505 00. If your manual requires a specific approval (for example, VW 504 00/507 00 or MB 229.52), choose an oil that explicitly lists it on the label. A generic “5W-40” without the right approvals is not a safe substitute.

Climate and driving profile

Ambient temperature and driving style help determine whether 5W-30 or 5W-40 is better for you.

• Cold climates: 5W-30 and 5W-40 crank similarly, but in extreme cold a 0W grade may be superior.
• Hot climates/high loads: 5W-40 often maintains thicker oil film at sustained high temperature.
• Short-trip, stop‑and‑go driving: Sticking with the OEM’s lower-viscosity recommendation can aid efficiency.
• Track days or mountain towing: 5W-40 (with the right approvals) can add a margin of thermal protection.

Selecting viscosity around your real-world conditions, within the OEM’s approved range, yields the best balance of protection and efficiency.

Warranty and emissions system considerations

If your vehicle is under warranty, use only viscosities and approvals listed by the manufacturer. For DPF/GPF-equipped vehicles, ensure the oil is the correct low-SAPS formulation (commonly ACEA C3/C5 with the proper OEM code). Using a non-approved 5W-40 can increase particulate filter ash over time and may jeopardize emissions-system longevity and compliance.

Practical steps to decide

Use this process to determine whether 5W-40 is appropriate in place of 5W-30.

1. Read the owner’s manual viscosity chart and specification section.
2. Check the oil filler cap and under-hood labels for approved grades.
3. Match the exact API/ACEA category and OEM approval required by your vehicle.
4. Consider climate and usage; favor 5W-40 for sustained heat/load if the manual allows it.
5. If under warranty, stay within listed options; when out of warranty, weigh benefits vs. economy.
6. After switching, monitor oil level, sound, and fuel economy over a few tanks.
7. For top-ups, mixing small amounts of 5W-40 into a 5W-30 fill is safe; keep to the required spec.

Following these steps ensures the oil change supports both engine health and compliance with manufacturer requirements.

After switching, what to watch for

Observing your vehicle’s behavior will confirm whether the change suits your engine.

• Oil pressure: A slight rise at operating temperature is normal; large changes warrant a recheck.
• Noise: Equal or reduced valvetrain/turbo noise under heat/load is a good sign.
• Consumption: Many engines use less oil with 5W-40; if consumption increases, revert to 5W-30.
• Fuel economy: Expect a small decrease; if it’s significant, reconsider.
• Cold behavior: Starts should remain normal; any sluggishness in very cold weather suggests a 0W grade.
• Emissions/DPF: For diesels, ensure the oil is low SAPS; note any increase in regeneration frequency.

These checks help you confirm the substitution is delivering the expected protection without undesirable side effects.

Myths vs. facts

Here are common misconceptions about switching from 5W-30 to 5W-40.

• Myth: Higher numbers always mean better protection. Fact: Only if the oil also meets the required OEM/ACEA specs and suits the engine design and climate.
• Myth: 5W-40 ruins cold starts. Fact: Both are 5W; cold-cranking performance is broadly similar within the grade.
• Myth: You’ll void the warranty no matter what. Fact: Using an OEM-approved 5W-40 listed in the manual preserves warranty.

Understanding the nuances helps you choose based on engineering requirements, not marketing or hearsay.

Summary

You can use 5W-40 instead of 5W-30 if—and only if—your vehicle’s manual approves it for your engine and conditions, and the oil meets the exact API/ACEA and OEM specs required. Expect slightly higher operating viscosity with potential benefits under heat and load, balanced against a small fuel-economy penalty. Pay special attention to emissions-system compatibility (low SAPS where required) and warranty terms. When in doubt, follow the viscosity and approvals printed in your owner’s manual.

What oil can you use instead of 5w30?

You should consult your car’s owner’s manual to find the manufacturer’s recommended oil viscosity, which is the most critical factor. While a 10W30 might be a suitable substitute in warmer climates or for older, high-mileage engines, using a 5W30 offers better cold-weather protection. Other options like 0W30 provide thinner cold-viscosity and 5W20 is thinner than 5W30 at operating temperatures, but it’s best to avoid drastic changes in oil weight. 
Consider your environment and engine age 

• For Warm Climates: If you live in an area where temperatures rarely drop below freezing, a 10W30 oil can be a suitable substitute for 5W30 because the “30” viscosity rating is the same at operating temperature. 
• For Cold Climates: If your region experiences regular temperatures below 0°F (-18°C), you should stick with 5W30 or a thinner, like 0W30, for better cold-start protection. 
• For High-Mileage Engines: Some mechanics suggest 10W30 might offer marginal benefits for older, higher-mileage engines with potential oil consumption or blow-by issues. 

Potential alternatives

• 10W30: A safe option in warmer climates or for older, high-mileage engines, as the operating viscosity is the same as 5W30. 
• 0W30: This oil is even thinner than 5W30 at cold temperatures, which can provide better cold-start protection and potentially offer more horsepower due to less friction. 
• 5W20: This is a thinner oil than 5W30 at operating temperatures. It’s best to use it only if your vehicle’s manufacturer specifically recommends it, as it’s not a direct substitute. 

Important considerations

• Consult the Owner’s Manual: Always check your vehicle’s owner’s manual for the exact viscosity recommended by the manufacturer. 
• Avoid Dramatic Changes: Avoid making large jumps in viscosity, such as going from a 0W20 to a 20W50. 
• Maintain Oil Quality: When using a substitute, consider a high-quality synthetic oil and a top-grade oil filter to help protect your engine, according to Quora. 

Is 5w30 or 5w40 better for old cars?

Recommended for 5W30: New vehicles, urban commuting, fuel efficiency prioritization, Japanese/Korean/American models. Recommended for 5W40: Older vehicles, turbocharged engines, high-temperature/long-distance driving, German models.

Can you mix 5W-40 and 5w30?

Yes, you can technically mix 5W30 and 5W40 engine oil, especially for a quick top-off in an emergency, but it’s not recommended for regular use as it slightly thickens the oil at high temperatures compared to 5W30. To avoid potential issues and maintain optimal engine performance, it’s best to stick to the single viscosity recommended by your car’s manufacturer for your vehicle and climate. 
Why mixing is generally a bad idea:

• Reduced performance: Mixing creates a hybrid viscosity (like a “5W-35”), which might not provide the specific level of protection and performance your engine was designed for, particularly at high temperatures. 
• Potential for issues: Some experts suggest that mixing oils can alter their additive balance and potentially lead to carbon buildup, though this is less of a concern with synthetic oils from the same brand. 
• Follow the manufacturer’s advice: The specific oil viscosity listed in your owner’s manual is crucial for ensuring the engine’s optimal operation and longevity. 

When mixing might be necessary:

• Emergency top-off: If you need to add a small amount of oil and the correct type isn’t available, a mix is better than running the engine low on oil. 
• Common base oils: You can safely mix different viscosities as long as they are the same type (e.g., both fully synthetic) and share the same viscosity rating at cold temperatures, like both being “5W” oils. 

What to do if you must mix:

• Check compatibility: Ensure both oils share the same cold-temperature rating (“5W” in this case) and are from the same brand and formulation if possible. 
• Address the mix soon: Top off the oil in an emergency, but plan for an oil change with the correct viscosity as soon as possible. 

When should you use 5w40 oil?

5w40 is better for starting your engine at low temperatures as it flows more easily in this environment. When the engine is running and hot, the differences are negligible; 5w40 and 10w40 both have high viscosities and are equally effective in protecting against engine wear.