The measure of the rate of change of viscosity with temperature. For example, the higher the VI the less tendency for the lubricants viscosity to change in the presence of thermal fluctuations.
Relationship between viscosity change of an oil with change in temperature; an empirical measure of the temperature coefficient of viscosity.
Arbitrary number that describes the rate at which oilís viscosity changes with changes in temperature. High VI oils are desirable because they display less viscosi‚ty change with temperatures.