How to choose engine oil from your car manual

You don't choose the right oil by brand or price but by two details in your car manual: the carmaker's specification and the viscosity.

1. Find the carmaker's specification

Look in the manual or service book for a code such as VW 504 00, MB 229.51, BMW LL-04, GM dexos2 or Renault RN17. The specification matters more than viscosity: it covers ash content, protection of the particulate filter and whether the oil can last an extended service interval.

If the maker gives only a general category such as ACEA C3 or API SP, the oil must meet at least that.

2. Check the viscosity

Viscosity is written as 5W-30 or 0W-20. The first number with W describes cold starting (lower = easier start in frost), the second the thickness at the 100 °C operating temperature.

If the manual allows several grades, climate and driving style decide. Do not use a thinner oil than the carmaker specifies, even if it saves fuel.

3. Compare the oils that meet it

The specification page lists every oil that meets it according to its data sheet. In the class table you can compare HTHS, TBN, pour point or ash and put up to four oils side by side.

Before buying, always check that the specification is printed on the label itself. Manufacturers update their data sheets over time.