Motor oil viscosity grades explained
An SAE grade like 5W-30 has two numbers. The number before the W (winter) shows how easily oil pumps at low temperature; the number after shows its thickness at high temperature. Pick the grade your car maker recommends for your climate.
| Grade | Cold (W) rating | Hot viscosity | Typical use / climate |
|---|---|---|---|
| 0W-16 | W = winter; flows at very low temp | Very low hot viscosity | Hybrid/modern engines; best fuel economy, mild climates |
| 0W-20 | Winter rating, pumps cold to -40C class | Low hot viscosity | Newer petrol engines; cold climates, fuel saving |
| 5W-20 | Winter grade, good cold flow | Low hot viscosity | Many US/JP petrol engines; moderate climates |
| 5W-30 | Common winter grade | Medium hot viscosity | Most modern petrol/diesel; wide climate range |
| 0W-30 | Winter grade, very cold flow | Medium hot viscosity | Cold regions; long-drain modern engines |
| 5W-40 | Winter grade, broad use | Higher hot viscosity | Turbo petrol/diesel; hot climates, towing |
| 10W-30 | Pumps at moderately cold temp | Medium hot viscosity | Older engines; temperate climates |
| 10W-40 | Standard winter grade | Higher hot viscosity | Older/high-mileage engines; warmer areas |
| 15W-40 | Needs warmer start | High hot viscosity | Diesel, trucks, older engines; hot climates |
| 20W-50 | Thick, warm-start only | Very high hot viscosity | High-temp, heavy load, older V8; hot climates |
Notes
- Always follow the vehicle manual; using too thick an oil can hurt fuel economy and cold starting.
- Synthetic oils keep their grade better across temperatures than conventional oils.
Frequently asked questions
- What does the W in 5W-30 mean?
- W stands for winter; the number before it (5) shows the oil's cold-temperature pumping grade, tested at low temperatures.
- Which number is the hot viscosity?
- The number after the W (30) is the high-temperature viscosity grade, measured at 100°C.
- Can I use a thicker oil than recommended?
- Not advised. Thicker oil can reduce fuel economy and may not flow well at cold start; follow the maker's spec.
- Is 0W-20 better than 5W-30?
- Neither is universally better; 0W-20 flows easier in cold and saves fuel, but only use a grade your engine is approved for.