5W30 vs 5W20
Verdict: Use whichever grade your owner's manual specifies. The two oils flow the same when cold, but 5W-20 is thinner at operating temperature, while 5W-30 is thicker and leaves a heavier film.
In both grades the first number with the W (for winter) describes how easily the oil flows in the cold. Both read 5W, so cold-start flow is rated the same. The second number is viscosity at normal engine temperature, about 212 degrees F, and that is where 20 and 30 differ.
A 20 is thinner when hot than a 30. Thinner oil can help fuel economy and suits modern engines built with tight tolerances. A 30 gives a thicker film. Engines are designed around one grade, so the manual should win over general advice, and an occasional mix-up is unlikely to cause lasting harm.
5W30 vs 5W20 side by side
| Trait | 5W30 | 5W20 |
|---|---|---|
| Cold rating (first number) | 5W | 5W |
| Rated viscosity at 100 C (212 F) | Thicker (30 grade) | Thinner (20 grade) |
| Cold start flow | Same winter rating as 5W-20 | Same winter rating as 5W-30 |
| Film at operating temperature | Thicker protective film | Thinner film |
| Fuel economy tendency | Slightly less benefit | Thinner oil helps fuel economy |
| Typical fit | Older or many general-purpose engines; 5W-30 is the most common grade | Newer engines designed for lighter oil |
| Who decides | Owner's manual | Owner's manual |
| Swapping from the other grade | Occasional one-grade change should not cause lasting damage, but use the specified grade | Same, use the specified grade |
Last verified October 2026. Typical values; individual animals, products and local prices vary.
Which one fits you
5W30
- Your owner's manual or oil cap specifies 5W-30
- You want a slightly thicker film at operating temperature in an engine rated for it
- You drive an older engine whose manual lists 5W-30 as the standard grade
- A previous owner or shop already ran 5W-30 and the manual allows it
5W20
- Your owner's manual or oil cap specifies 5W-20
- Your engine is a newer design with tight tolerances built for lighter oil
- You want the small fuel economy benefit a thinner oil gives within the manual's spec
- You are replacing 5W-20 that the manufacturer called for
How this works
The quiz uses cues that point to the grade your engine was built for: the manual, the cap or sticker, and the engine's age. It cannot know your specific engine, so a manual answer outweighs everything else here. Treat the quiz as a prompt to check the manual, not a replacement for it.
Viscosity grade is only one part of an oil spec. Your manual may also require a performance standard or synthetic oil, so match those as well as the numbers. Viscosity grade is only one part of an oil spec. Your manual may also require a performance standard or synthetic oil, so match those as well as the numbers shown here.
Where these numbers come from
The figures and defaults on this page are based on:
- U.S. Lubricants: What Does 5W-30 Mean? Engine Oil Grades Explained, Explains the W number, operating-temperature number and checking the manual. (checked October 2026)
- AMSOIL Blog: 5W-20 vs 5W-30 vs 10W-30, Compares cold and hot viscosity, fuel economy and manual advice. (checked October 2026)
General information, not mechanic advice. Both sources are oil industry publishers, so the owner's manual is the authority for your vehicle.
Frequently asked questions
What do the numbers in 5W-30 and 5W-20 mean?
The 5W is the oil's cold-temperature rating, with W standing for winter, and lower numbers flow better when cold. The 30 or 20 is the viscosity at normal operating temperature, about 212 degrees F.
Can I use 5W-30 instead of 5W-20?
Both have the same cold rating. The best practice is the grade in your owner's manual. Using one grade higher or lower occasionally should not cause lasting damage, but it is not what the engine was designed for.
Does 5W-20 give better gas mileage?
Thinner oil generally helps fuel economy, so 5W-20 has a slight edge in an engine designed for it. The effect is small, and it does not apply if your engine calls for 5W-30.
Is 5W-30 or 5W-20 better in winter?
Neither has an edge at start-up, because both carry the same 5W rating. The difference shows up once the engine is hot.
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