@twincamhq: What do the numbers on engine oil bottles actually mean? When you buy a bottle of motor oil, you have to find the correct grade for your car, and it’s defined by a set of numbers. But what do they actually mean, and why’s there often a ‘W’ in the middle? It's a measurement of the oil’s viscosity, its thickness, and this metric was developed by the Society of Automotive Engineers, hence back in the day, an oil can may have said ‘SAE 20’, which was thinner than ‘SAE 50’. These measurements are taken at 100⁰C, but when you start your car on a cold morning, the oil is not 100⁰, so to ensure it adequately lubricates the engine, and so you can use the same grade year-round, modern oils use additives known as viscosity modifiers to produce a multi-grade oil – something like 5W-30. The suffix is therefore the high-temperature viscosity, while the prefix, with a ‘W’ for ‘winter’, is an equivalent at something in the region of -30⁰C. If you’ve owned a number of cars over the years, it’s likely you’ll have noticed that modern cars tend to use very thin oils, partly due to tighter tolerances within modern engines, but also to maximise fuel economy and minimise emissions. You see, the engine’s components have to move through the oil, so if it’s gloopy, it’ll sap power, and if it’s thin, it may not properly lubricate, so next time you need a top-up, think about what’s going in. Or just read the handbook.

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Friday 28 August 2026 19:00:06 GMT