What do numbers on oil mean

Different cars require different kinds of motor oil , which is why those numbers on the bottle are so important. Jason Fenske at Engineering Explained has a quick video explanation of what those numbers mean. Note that the video is sponsored by Mobil1, though Jason uses the video to explain oil weights rather than extol the virtues of one brand of oil over another.

The numbers refer to what's known in the industry as the oil "weight," but that term is a bit misleading. Oil weight doesn't refer to how heavy an oil is; it's a measure of viscosity, or the thickness of a fluid.

Syrup, for example, has a high viscosity, while water has a low viscosity. The higher the number on the bottle, the thicker the oil. However, the numbers are also temperature dependent.

A 10W rating means an oil has a viscosity grade of 10 in cold temperatures "W" stands for "winter" , and 30 in warm temperatures. That doesn't mean the oil gains viscosity as it heats up, though.

It just means the oil will behave like a weight when cold and a weight when hot. In general, oil's viscosity actually decreases as it heats up. Manufacturers typically uses additives to achieve temperature-specific viscosity ratings, and those ratings are certified with multiple tests.

Cold testing usually ranges from degrees Celsius to degrees Celsius 14 degrees Fahrenheit to degrees Fahrenheit , according to Fenske. Testers want to see if the oil will be thin enough for the engine to turn over, and to flow once the engine is running. This is why you would see something like this on the label: SAE 5W In a 5W for example, the number before the W describes the viscosity of the oil at low temperatures.

Multigrade oils such as SAE 5W and 10W are widely used because, under all but extremely hot or cold conditions, they are thin enough to flow at low temperatures and thick enough to perform satisfactorily at high temperatures. Pay attention! Your browser is outdated, this can have a negative effect on the user experience. Download Google Chrome. Overhead engines. Because the oil needs to travel to the overhead cams and valve train, most mechanics recommend a lower weight for overhead engines.

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