Engine oil fulfills several important functions in a car engine, as it not only lubricates the internal parts of the engine, but also, for example, cleans and provides cooling.
When it’s time to top up or change the oil, it’s easy to get confused by the different grades of motor oil available to choose from.
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A matter of viscosity
What the motor oil numbers indicate is its viscosity, or how viscous it is, at different temperatures.
The format is usually a one- or two-digit number combined with a W, followed by a hyphen and a two-digit number.
The first number in combination with W indicates the viscosity of the oil when it is completely cold. The second number indicates the viscosity of the oil when the engine is up to operating temperature, more specifically at 100 degrees Celsius.
In most cases, the best choice for an everyday car is to simply buy the engine oil recommended in the car’s owner’s manual.
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The W number is important in winter
There is one exception though, and that is if you live in a place that experiences extremely low temperatures. Then you have to think about it when choosing engine oil.
The W on the motor oil stands for “winter”, or “vinter” in Swedish, and is especially important for cars that are driven in the winter. Oil becomes more viscous the colder it gets.
If you choose an oil that is too thick when it is cold, there is a risk that it will not lubricate the engine properly at low temperatures, as the oil pump will not be able to pump it around properly. This in turn leads to great engine wear during cold starts.
The most easily flowing oil at a cold start is designated 0W, and lubricates properly all the way down to -35 degrees Celsius. The designations rise after this in powers of five. 5W can handle cold start down to -30 degrees, 10W down to -25 and so on.
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