All lubricants for car engines are multigrade (10W40 / 15W60 / 5W30). Without getting overly technical, this is the most important characteristic of the lubricant and one which determines where it is used. Before multigrades, it was necessary to change a monograde oil according to the season. Since a lubricant liquifies according to the temperature of the engine, it was crucial to precisely evaluate these properties with a viscosity grade (SAE) common to all of them.
In fact two exist, with, on one hand, a viscosity grade of 0W to 25W for low temperatures (the letter W stands for Winter) and, on the other, a summer grade which can vary from 20 to 60. Winter grades indicate the properties that are critical for starting a cold engine, while summer grades show the viscosity of the lubricant at its normal functioning temperature.
A multigrade lubricant thus offers a wide spectrum of utilisation with different performance capabilities. For example, 5W30 and 15W60 do not have the same features and so automobile manufacturers precisely determine the viscosity grade which is perfectly suited to each engine and it is crucial to respect those guidelines.
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