VISCOSITY INDEX: ASTM D2270
(Equivalent Test Methods: IP 226, ISO 2909, and AFNOR T60-136)
EXPLANATION
The Viscosity Index is a widely used and accepted measure of the variation in kinematic viscosity due to changes in the temperature of a petroleum product between 40 and 100° C. Viscosity index is an arbitrary number used to characterize the variation of the kinematic viscosity of a petroleum product with temperature. For oils of similar kinematic viscosity, the higher the viscosity index the smaller is the effect of temperature on its kinematic viscosity. This practice specifies the procedures for calculating the viscosity index of petroleum products, such as lubricating oils, and related materials from their kinematic viscosities at 40 and 100° C.
TEST PRECISION
The calculation of viscosity index from kinematic viscosities at 40 and 100° C is exact, and no precision limits can be assigned to this calculation.
The accuracy of the calculated viscosity index is dependent only on the accuracy of the original viscosity determination. Test Method ASTM D445 has a stated repeatability limit of 0.35 % and a reproducibility limit of 0.70 %.
The calculation of viscosity index from kinematic viscosities at 40 and 100° C is exact, and no bias can be assigned to this calculation.
