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Workshop: Oil Part V – How To Read An Oil-Can Label


Words Freddi Stafford

I hope that this series of articles on what seems to be the simple subject of oil has proved that when it comes to technology, our world has changed forever. This final article on the subject of automotive lubricants aims to summarise how to read and understand the label on an oil can.

That’s because brand and specification, if chosen correctly, will affect our vehicle’s service life, reliability, ongoing maintenance costs and fuel consumption, and help ensure the safety of all those whom we transport. In other words, make our lives more convenient.

One of my favourite writers, Isaac Asimov, had this pertinent comment to make: “The saddest aspect of life right now is that science gathers knowledge faster than society gathers wisdom.” This has a direct bearing on the subject of motor oils: a very difficult topic to comprehend.

Most people in the industry (including respected mechanics) think that they are experts in this field, but very few actually understand or have any idea of the complexity of engine oils. In fact, some of them will never be able to understand the theory. So, when we look at a can of oil before making the important decision to purchase it and place it in our vehicle, are we basing our decision on what feels right, a friend’s recommendation, the spares shop assistant’s endorsement, an advertisement, the brand our father used, the mostly marketing drivel on the can itself… or is our decision based on knowing something about oil? Here then, is an easy opportunity to gather wisdom and know something about oil.

What’s written on an oil can – or, in many cases, what is not written – will provide you with the answers you need. Besides the brand and product name, the packaging of all automotive lubricants should mention the purpose for which it is intended – such as motor oil, manual or automatic transmission oil, differential oil, etc.

The base oil type should be shown on the can: mineral, semi-synthetic, synthetic technology or fully synthetic. The viscosity should be shown clearly: 20w/50 or 5w/40 etc. for engine oils, and 75w/90 or 85w/140 etc. for gear oils.

All engines are not the same, so it shouldn’t be a surprise that oils are not the same, either. With this in mind, we should be able to see the performance specification, including those of the API (American Petroleum Institute) and ACEA (or Association des Constructeurs Européens d’Automobiles, in French). The API’s engine-oil quality marks (specifically the API Service Symbol “Donut” and Certification Mark “Starburst”) help consumers identify to quality engine oils for their petrol- and diesel-powered vehicles.