5W-20 vs 5W-30 Engine Oil
Reviewed by GarageDex editorial
5W-20 and 5W-30 flow the same when cold (both 5W); 5W-30 is thicker when hot. Use the grade your engine specifies - they are not interchangeable for long-term use.
| 5W-20 | 5W-30 | |
|---|---|---|
| Cold-start flow | 5W (same) | 5W (same) |
| Thickness when hot | Thinner (20) | Thicker (30) |
| Fuel economy | Slightly better | Slightly lower |
| High heat / towing | Adequate | Stronger film |
Both share the 5W cold rating, so start-up flow is identical. The difference is hot thickness: 5W-30 holds a thicker film at operating temperature, which helps under sustained heat, towing, or high RPM, while 5W-20 reduces drag for slightly better mileage.
Engines are designed around one or the other. A 5W-20 engine running 5W-30 sees higher oil pressure and a small economy loss; a 5W-30 engine running 5W-20 may have a thinner film than intended under load.
Which should you use?
Match the manual. Neither is universally better - it depends on the clearances your engine was built for.
Frequently asked
Can I mix 5W-20 and 5W-30?
A one-time mix in an emergency will not harm the engine, but you should return to the specified grade at the next change for correct protection and economy.
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