How to read: 5W-30
5W
is the winter grade (W - winter): the lower the number, the lower the temperature at which the oil stays pumpable and the starter can crank the engine. 30 is the summer grade: working viscosity at 100 °C. Together they make a multigrade oil good for both frost and a hot engine.
SAE winter grade
| Grade | Cold start down to | Pumpable down to |
|---|---|---|
| 0W | −35 °C | −40 °C |
| 5W | −30 °C | −35 °C |
| 10W | −25 °C | −30 °C |
| 15W | −20 °C | −25 °C |
| 20W | −15 °C | −20 °C |
SAE summer grade
| Grade | Viscosity at 100 °C, mm²/s |
|---|---|
| 20 | 5.6-9.3 |
| 30 | 9.3-12.5 |
| 40 | 12.5-16.3 |
| 50 | 16.3-21.9 |
API and ACEA
| Marking | Meaning |
|---|---|
| API S… | petrol engines; a later letter means a newer standard: SL → SM → SN → SP |
| API C… | diesel engines: CI-4, CJ-4, CK-4 |
| ACEA A/B | petrol/diesel passenger cars, full SAPS: A3/B4 - robust oils for older engines |
| ACEA C | low SAPS - low-ash oils for cars with a particulate filter and catalyst: C2, C3, C5 |
The approval matters most
Viscosity and API are the baseline; a specific engine needs oil with the carmaker's approval (e.g. Renault RN0700/RN0710, VW 504 00, MB 229.51). The approval is printed on the label - look for it, not for a "suitable for" claim.
Less ash - longer filter life
If the car has a DPF/GPF, use only low-ash ACEA C oils - full-SAPS A3/B4 gradually clogs the filter with incombustible residue.