Comparisons
5W-30 vs 5W-40 Engine Oil: What's the Difference?
Understand the difference between 5W-30 and 5W-40 engine oil and why viscosity matters.
Learn how oil grades affect lubrication and how to select the correct oil for your vehicle.
Quick Answer
5W-30 and 5W-40 oils share the same cold-start viscosity rating but differ in how they behave at normal operating temperatures. The higher second number indicates that 5W-40 generally maintains a thicker oil film at higher temperatures compared with 5W-30. However, this does not mean it is automatically better for every engine. The most important factor is using an oil viscosity and specification approved by the vehicle manufacturer. Selecting the wrong oil can affect lubrication performance, fuel economy, and long-term engine durability.
5W-30
- Commonly specified for many modern passenger vehicles.
- Often supports fuel-efficiency targets.
- Provides good cold-start performance.
- Frequently recommended by manufacturers.
5W-40
- Maintains a thicker viscosity at operating temperature.
- Common in some high-performance and heavy-duty applications.
- May be specified for certain engines and operating conditions.
- Not a universal upgrade over 5W-30.
Key Differences
- Hot operating viscosity.
- Manufacturer application requirements.
- Potential fuel economy differences.
- Engine-specific suitability.
Best For / Which Should You Choose?
- Follow the viscosity specified in the owner's manual.
- Consider climate, engine design, and manufacturer approvals.
- Avoid changing viscosity solely based on internet recommendations.
Sources
- Mobil — Motor Oil Viscosity Guide — Mobil Motor Oils
- Shell — Engine Oil and Lubricants Information — Shell Lubricants
FAQs
- Can I switch between 5W-30 and 5W-40?
- Only if both viscosities are approved by the vehicle manufacturer for that engine.
- Does thicker oil provide more protection?
- Not always. Engine designs are developed around specific oil viscosity ranges.
Still not sure what this means for your car?
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