5W-20 and 0W-20 are the same thickness at full operating temperature (both are 20-grade), but 0W-20 flows better in extreme cold while 5W-20 is slightly thicker when cold. Use whichever grade your owner's manual specifies for your engine and climate.
Attribute
5W-20
0W-20
Cold-start flow The lower first number flows better at low temperatures.
5W — very good cold flow
0W — best in extreme cold
Hot viscosity (100 °C) Both give the same film thickness when hot.
20 — identical
20 — identical
Extreme-cold suitability
Good, slightly behind 0W
Best for very cold winters
Typically specified for
Many engines tuned for a 20-grade
Same engines, with an edge in harsh cold
Bottom line: Same hot thickness, different cold flow — follow the grade your manual specifies for your climate.
The one real difference
Both oils are 20-grade, so at full operating temperature they hold the same film thickness — there is no hot-running difference between them. The only meaningful difference is cold behavior. 0W-20 has the lower first number, so it stays thinner and pumps faster when the engine is very cold; 5W-20 is slightly thicker at low temperatures.
For most drivers in mild or moderate climates, both grades reach healthy oil pressure quickly and the difference is small. The 0W advantage shows up in genuinely cold winters, where its faster cold flow gets oil to the top of the engine sooner after start-up.
Which should you use?
Use the grade your owner’s manual specifies for your engine and climate. Because the two share identical hot viscosity, the choice is essentially about cold-start performance, and the 0W grade is the safer pick when winters are severe.
Many manuals list 0W-20 as the primary recommendation and allow 5W-20 as an alternative, or vice versa, sometimes tied to a temperature range. If yours lists both, either is fine within the stated conditions; in very cold weather, lean toward 0W-20. Remember that viscosity is separate from specification: whichever grade you choose still has to meet the oil standard or approval your manual requires.
Frequently asked questions
Is 0W-20 thinner than 5W-20?
Only when cold. 0W-20 stays thinner at low temperatures and flows faster on a cold start. When hot, both are the same thickness because both are 20-grade.
Can I use 5W-20 instead of 0W-20?
Only if your manual lists 5W-20 as acceptable. They match when hot, but 0W-20 flows faster in extreme cold, so the 0W grade has an advantage in harsh winters.