What the numbers mean
- The first number with the W (“winter”) rates how the oil flows when cold. Lower means it flows faster at start-up, when most engine wear happens.
- The second number rates thickness at normal operating temperature. Lower means thinner.
So 0W-20 is easier-flowing on a cold morning and thinner when warm than 5W-30.
Can you switch between them?
Stick with what the manual specifies. Engines built for 0W-20 have tighter clearances and systems (like variable valve timing) designed around that thinner oil; using a thicker oil can reduce fuel economy and may not protect as intended. An engine designed for 5W-30 may not be adequately protected by a thinner oil.
Some manuals list more than one acceptable grade, or alternatives for very hot or cold climates. If yours does, any listed grade is fine.
Common questions
I put 5W-30 in a 0W-20 engine. Is it ruined?
Very unlikely from one oil change. Go back to the specified grade at the next change.
Is thicker oil better for a high-mileage engine?
It’s sometimes suggested, but your manufacturer’s grade is still the place to start. Ask a qualified mechanic if the engine is using a lot of oil — see our high-mileage plan.
Where do I find my car’s grade?
In the owner’s manual and often on the oil filler cap. See what oil does my car take.