ASTM D2270 Practice for Calculating Viscosity Index from Kinematic Viscosity at 40ºC and 100ºC
Oil viscosity (see ASTM D445) typically decreases as temperature increases. If this decrease is large, the system may not be properly lubricated over the entire operating temperature range. Viscosity index describes this change – a high viscosity index indicates a smaller viscosity change with temperature increase than a low viscosity index. This method determines the viscosity index of lubricating oils that conform to the general properties of Newtonian fluids. It is a calculation applied to the viscosities that have been determined by ASTM D445.