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where U is the oil's kinematic viscosity at 40 °C (104 °F), Y is the oil's kinematic viscosity at 100 °C (212 °F), and L and H are the viscosities at 40 °C for two hypothetical oils of VI 0 and 100 respectively, having the same viscosity at 100 °C as the oil whose VI we are trying to determine.
Increasing temperature results in a decrease in viscosity because a larger temperature means particles have greater thermal energy and are more easily able to overcome the attractive forces binding them together. An everyday example of this viscosity decrease is cooking oil moving more fluidly in a hot frying pan than in a cold one.
Consequently, if a liquid has dynamic viscosity of n centiPoise, and its density is not too different from that of water, then its kinematic viscosity is around n centiStokes. For gas, the dynamic viscosity is usually in the range of 10 to 20 microPascal-seconds, or 0.01 to 0.02 centiPoise. The density is usually on the order of 0.5 to 5 kg/m^3.
The oil fails the test at a particular temperature if the oil is too viscous. The grade of the oil is that associated with the coldest temperature at which the oil passes the test. For example, if an oil passes at the specified temperatures for 10W and 5W, but fails at the 0W temperature, the oil is grade 5W. It cannot be labeled 0W or 10W.
The viscosity index is a measure of how much the oil's viscosity changes as temperature changes. A higher viscosity index indicates the viscosity changes less with temperature than a lower viscosity index. Motor oil must be able to flow adequately at the lowest temperature it is expected to experience in order to minimize metal to metal contact ...
Viscosity index (ASTM D2270 [11]) is a measure of the extent of viscosity change with temperature; the higher the VI, the less the change. VI is calculated from viscosity measurements at 40°C and 100°C. The viscosities of paraffinic and naphthenic base oils have very different behavior with temperature change.
Grape seed oil: 216 °C: 421 °F Lard: 190 °C: 374 °F [5] Mustard oil: 250 °C: 480 °F [11] Olive oil: Refined: 199–243 °C: 390–470 °F [12] Olive oil: Virgin: 210 °C: 410 °F Olive oil: Extra virgin, low acidity, high quality: 207 °C: 405 °F [3] [13] Olive oil: Extra virgin: 190 °C: 374 °F [13] Palm oil: Fractionated: 235 °C [14 ...
Under standard atmospheric conditions (25 °C and pressure of 1 bar), the dynamic viscosity of air is 18.5 μPa·s, roughly 50 times smaller than the viscosity of water at the same temperature. Except at very high pressure, the viscosity of air depends mostly on the temperature.