0W-20 is a thin, fuel-efficient multi-grade oil that flows like a 0-weight in extreme cold and protects like a 20-weight when hot. Many late-model engines are engineered specifically for it, so substituting a thicker grade is usually not recommended unless your manual says so.
Cold-start (winter) behavior
The "0W" gives excellent cold-start flow, ideal for very cold climates and quick lubrication on startup.
Grade anatomy
What 0W-20 means
0Cold-flow rating
WWinter test
20Hot viscosity grade
The first number describes tested cold-start behavior. The second number describes the
viscosity band at operating temperature; it is not a quality rating.
Commonly specified for
Many modern Toyota, Honda, Subaru and other late-model gasoline engines
Engines tuned for fuel economy (CAFE) and specifying API SP / ILSAC GF-6A
How to read “0W-20”
0W — the Winter rating. The 0 means it flows very easily in extreme cold, giving fast protection on cold starts.
20 — viscosity at full operating temperature (100 °C). It is thinner when hot than a 30-grade, which reduces internal drag and improves fuel economy.
Modern engines are often built with tighter tolerances designed around this thin oil.
Why so many new cars specify 0W-20
Thinner oil reduces pumping losses and friction, which helps fuel economy and emissions targets. Manufacturers engineer the oil pump, bearings, and clearances for the specified grade — which is why using a thicker oil than specified can work against the engine’s design.
Viscosity is not the same as specification
0W-20 describes thickness only. Your engine may also require a specification such as API SP, ILSAC GF-6A, or dexos1 Gen3. Match both the grade and the spec from your manual.
0W-20 from cold start to operating temperature
How 0W-20 behaves from cold start to operating temperature
Cold startOperating temp
At 20 °C the engine is near ambient — the 0W winter rating governs
how quickly 0W-20 reaches moving parts on start-up.