There is no possibility to calculate those viscosities on the basis of the ISO VG value alone. Because no viscosity index is defined, the viscosity at other temperatures then at 40 degrees C can differ quite considerably for the same ISO VG grade. The ISO viscosity grades just define a certain viscosity range at 40 degrees C.(nominal value plus or minus 10%). Oils with a lot of VI-improver usually exhibit this type of behaviour at low temperatures (ATF, multigrade engine oils). For non-Newtonian fluids this type of calculation is less accurate, especially at lower temperatures. If you know the viscosity of a Newtonian fluid at two different temperatures the equation can be solved and kinematic viscosities at other temperatures can be calculated. The socalled Walther equation describes the temperature-viscosity relationship of Newtonian fluids.
