DUNSHUN LUBRICANTSWhat 5W-30 Actually Measures Under SAE J300
Short answer: "5W" and "30" are two independent viscosity tests from SAE J300 — one at −30 °C for cold starting, one at 100 °C for hot operation. Neither number means thickness or quality by itself.
The "5W" — Winter (Cold-Start) Tests
The "W" stands for winter, not weight. For a 5W grade, SAE J300 limits two low-temperature measurements:
- CCS cranking viscosity at −30 °C: maximum 6,600 mPa·s — how hard the starter must work.
- MRV pumping viscosity at −35 °C: maximum 60,000 mPa·s — whether oil reaches the oil pump fast enough after a cold night.
A 0W oil just passes the same tests at a lower temperature (CCS at −35 °C). That's the whole difference between 0W-30 and 5W-30.
The "30" — Hot Viscosity at 100 °C
The second number is a kinematic viscosity window at 100 °C plus a high-temperature/high-shear (HTHS) limit at 150 °C:
- Kinematic viscosity at 100 °C: 9.3 – 12.5 mm²/s for an xW-30
- HTHS at 150 °C: ≥ 2.9 mPa·s for SAE 30 (fuel-economy ~2.9; standard ~3.5)
What This Means When Choosing a Grade
| Situation | Better choice | Why |
|---|---|---|
| Cold winters, frequent short trips | 0W-30 / 0W-20 | Faster oil pressure at −30 °C class starts |
| Hot climate, high mileage, heavy loads | 5W-40 | Higher hot viscosity holds film strength |
| Latest GDI / turbo engines with GPF | Follow OEM spec (often 0W-20 / 5W-30 API SQ) | Emission-system compatibility |
The grade is only half the story, though. The API/ACEA performance level (SJ → SQ) decides the additive chemistry; the SAE grade only decides flow. Match both to the OEM requirement.
Dunshun supplies 5W-30 in API SQ, SP+ and SL performance levels, plus CK-4 5W-30 diesel. Ask us which grade fits your market: contact.