Oils: What The Numbers Mean

One dizzying aspect of engine oil is the series of numbers and letters on the container. Adventure Rider Magazine set out to demystify the numerical classification on engine lubricants.

Last issue we had a look at the differences between synthetic and mineral oils. This issue we have a look at the letters and numbers on the label – because we’re, like, word geniuses, we’d say ‘the alpha-numeric designation’. After we’d said that we’d need a Bex and good lie down, but we’d’ve been right, as usual.

Capital letters

The letters are the easy part, so we’ll deal them first.

Oils are graded for viscosity – ‘thickness’ – using a scale set by the Society of Automotive Engineers. So that’s the ‘SAE’ part of your label.

The ‘W’ on some oils simply stands for ‘Winter’, and it specifies the oil’s viscosity when operating at about -30° Celsius. Commonly in Australia we’ll see ‘10W’ or ‘20W’.

The other letters which should be on the label of your oil container are either ‘API’ or ‘ACEA’. These stand for, respectively, ‘American Petroleum Institute’ and ‘Association des Constructoreurs d’Automobiles’. These two organisations represent the oil and natural-gas industries of their respective continents, and, along with a great deal of political lobbying and marketing to the general public, establish and certify standards for all kinds of things in their beaut, oily industries.

We don’t need to know any more about what they do or how they do it, but seeing those letters on a bottle of oil at the bike shop offers some reassurance the product in the bottle is what it claims to be.