0W-20 and 10W-30 differ on both axes: 0W-20 flows much better on cold starts and is thinner at operating temperature, while 10W-30 is thicker when hot and needs milder winter conditions to flow well. 0W-20 is common in modern fuel-economy engines, and 10W-30 appears in many older or higher-mileage engines — follow the grade printed in your owner's manual.
Attribute
0W-20
10W-30
Cold-start flow
0W — flows better when cold
10W — needs milder winters
Hot viscosity (100 °C)
20 — thinner when hot
30 — thicker when hot
Typical use
Modern fuel-economy engines
Many older or higher-mileage engines
Fuel economy
Lower friction can aid economy
Thicker oil, slightly more drag
How to choose
Use if your manual lists 0W-20
Use if your manual lists 10W-30
Bottom line: Different on both axes: 0W-20 flows better cold and runs thinner hot; 10W-30 is thicker hot and built for milder winters. Use your manual.
What the grades mean
0W-20 and 10W-30 differ in both numbers, so they behave differently in cold and in heat. The first number with the W describes cold-start flow: 0W flows more freely at low temperatures than 10W, so a 0W-20 engine cranks and circulates oil faster on a cold morning. The second number describes thickness once the engine reaches operating temperature: a 20 is thinner when hot than a 30.
That makes 0W-20 the lighter oil overall — easier flowing cold and thinner hot. 10W-30 sits a step heavier on both counts. Neither is “better” in the abstract. Each is correct only for engines designed around it.
Which one your engine needs
Use the grade printed in your owner’s manual. Many recent engines specify 0W-20 because lower-friction oil supports fuel economy, and their internal clearances are built for a thinner film. Plenty of older engines, and some higher-mileage ones, call for 10W-30, which gives a slightly thicker hot film suited to their design.
These two grades are not freely interchangeable. Putting 10W-30 in an engine that asks for 0W-20 can raise internal drag and may not match the maker’s economy and protection assumptions; putting 0W-20 in an engine built for 10W-30 may give a thinner film than intended. Some manuals list more than one acceptable grade or adjust the recommendation by climate — if yours does, follow that guidance.
When in doubt, the manual settles it. The grade on that page already accounts for your engine’s design and the temperatures it was built to handle, so match it rather than guessing by feel.
Frequently asked questions
Can I use 10W-30 instead of 0W-20?
Only if your manual lists 10W-30 as acceptable. They are not interchangeable by default — the engine is designed around a specific grade.
Is 0W-20 too thin to protect my engine?
No. In an engine designed for it, 0W-20 protects fully. Thinner is not weaker — the grade is matched to the engine's clearances.
Why does my new car call for 0W-20?
Many modern engines use thinner oil to reduce friction and improve fuel economy, with tighter tolerances designed for that grade.