Viscosity refers to the viscosity of an oil. Depending on the temperature, any oil changes its viscosity. As the temperature increases, it becomes more fluid. At the same time, its adhesion to metal and the ability to form an oil film under pressure deteriorate. In the cold, it becomes dense and viscous, poorly flowing, and the internal friction resistance increases. This property requires the use of an oil with such a viscosity that, with a change in temperature, changes its properties as little as possible.
With a cold engine, it should be fluid enough so as not to overload the work of the starter and so that after starting it reaches the rubbing parts as quickly as possible.
Viscosity or flowability is the same as the internal friction of the oil and is indicated by the SAE system (Society of Automobile Engineers), such as SAE30, SAE10, etc. High SAE numbers indicate thick oils, low SAE numbers indicate thin oils. At the same time, viscosity alone does not give a conclusion about the lubricating properties of the oil.
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