5W-40 vs 5W-30 Engine Oil
Reviewed by GarageDex editorial
5W-40 and 5W-30 flow the same when cold (both 5W); 5W-40 is thicker when hot. 5W-40 suits high-heat, turbo, diesel, and many European engines; 5W-30 is the common modern grade. Use the one your engine specifies.
| 5W-40 | 5W-30 | |
|---|---|---|
| Cold-start flow | 5W (same) | 5W (same) |
| Thickness when hot | Thicker (40) | Thinner (30) |
| High heat / turbo / diesel | Stronger film | Adequate |
| Fuel economy | Slightly lower | Slightly better |
Both share the 5W cold rating, so start-up flow matches. The difference is hot thickness: 5W-40 holds a thicker film at temperature, which helps under sustained heat, high RPM, turbocharging, or in many diesels, while 5W-30 reduces drag for slightly better economy.
Engines are designed around one or the other. Many European and performance engines call for 5W-40; most mainstream modern engines specify 5W-30 or thinner.
Which should you use?
Match the manual. Use 5W-40 where it is specified (often Euro/turbo/diesel or hot-climate use); use 5W-30 where that is the listed grade.
Frequently asked
Is 5W-40 better than 5W-30?
Not universally - it is just thicker when hot. It is better for engines designed for it (high heat, turbo, diesel); in an engine that specs 5W-30 it can slightly reduce fuel economy without adding benefit.
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