0W-20, 5W-30, C3, C5: choose engine oil by spec, not by viscosity

“It takes 5W-30” is the most common thing we hear on the phone — and it is only half the answer. Viscosity tells you how thick the oil is. The specification tells you what it is made to do.

Reading viscosity

In 5W-30, the first number (with the W, for winter) is how easily the oil flows cold; lower is thinner. The second number is how thick it stays at operating temperature. Modern engines with tight tolerances are designed around thin oils — using something thicker can slow oil getting to the turbo and variable valve timing at start-up.

Reading the specification

The spec is the part that matters for warranty and for protecting emissions equipment. In Europe you will see ACEA grades and manufacturer approvals:

Our advice

1. Start with the handbook or service schedule, not the viscosity on the old bottle.
2. Match the manufacturer approval first, then the ACEA grade, then viscosity.
3. Do not “upgrade” a 0W-20 engine to 5W-30 thinking thicker is better, or the other way round.
4. Always change the filter with the oil.

Not sure? Call the parts desk with the reg and we will tell you exactly which oil and how many litres.