![]() Thanks to the synthetic base oils and the viscosity modifier additives, nowadays most motor oils are so-called multigrade oils that don’t change their viscosity with temperature that much, so they meet the limits of a winter and that of a summer viscosity grade at the same time. These products were monograde oils and car owners had to change oil at least twice a year: once for the winter and once for the summer. Several decades ago motor oils either fell in one of the winter viscosity grades or in one of the summer viscosity grades. The numbers that have a W after them are the so-called winter viscosity grades while the numbers that don’t have a W are the so-called summer- or operating temperature viscosity grades. SAE J 300 - Table of engine oil viscosity grades Low-Shear-Rate Kinematic Viscosity (cSt) at 100 ☌ max. Low-Shear-Rate Kinematic Viscosity (cSt) at 100 ☌ min. Low-Temperature (☌) Pumping Viscosity, cP max with no yield stress Low-Temperature (☌) Cranking Viscosity cP max. These limits are listed in the SAE J 300 table: SAE Viscosity Grade In case of engine oils, these grades, also known as “weights” were set by the SAE (Society of Automotive Engineers) and in order for a fluid to fall in a given category it has to meet certain limits. The viscosity is measured in mPa*s (millipascal-seconds) or its equivalent cP (centiPoise) but in everyday life we don’t use the actual measured viscosity, we use viscosity grades instead. In case of lubricants the viscosity is very important because it affects the oil’s ability to reduce friction and transfer heat. To find out which oil and which viscosity you should use for your vehicle, refer to the manufacturer's service manual.Viscosity is a fluid’s resistance to flow. The numbers to the right of the letter “W” are its hot grade.The higher the grade, the more viscous the oil will be at high temperatures. The lower the viscosity when cold, the more fluid the oil is at low temperatures and the more easily it can be pumped.Greater levels of fluidity at low temperatures make cold starts easier. The viscosity designation is made up of two numbers separated by the letter “W” (for “Winter” for the cold grade).The numbers that come before the W refer to the product’s cold grade, i.e., its viscosity at low temperatures. The SAE (Society of Automotive Engineers) has developed a means of classifying lubricants in order to specify their viscosity levels when hot and when cold. It should remain fluid at low temperatures (to make cold starts easier) and viscous at high temperatures (in order to provide protection and sealing).The grades that have been optimized for each of your oils are detailed in your service manual. To ensure that your vehicle performs optimally, your oil should retain a certain level of viscosity in all weather conditions: Viscosity varies according to temperature in the following way: the higher the temperature, the more fluid and less viscous the oil will be. An oil can, in effect, be characterized by its viscosity, its flow resistance or by the thickness of its oil film. ![]() Lubricants behave differently at high and low temperatures. Engine Oil Viscosity/ Motor Oil Viscosity
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