ASTM D2270 for calculating viscosity index from kinematic viscosity at 40 and 100°C
5. Procedure A - For Oils of Viscosity Index Up to and Including 100
5.1 Calculation:
5.1.1 If the kinematic viscosity of the oils at 100°C is less than or equal to 70 mm2/s (cSt), extract from Table 1 the corresponding values for L and H. Measured values that are not listed, but are within the range of Table 1, may be obtained by linear interpolation. The viscosity index is not defined and may not be reported for oils of kinematic viscosity of less than 2.0 mm2/s (cSt) at 100°C.
5.1.2 If the kinematic viscosity is above 70 mm 2/s (cSt) at 100°C, calculate the values of L and H as follows:
L = 0.8353 Y(2) + 14.67 Y - 216
H = 0.1684 Y(2) + 11.85 Y - 97
where:
L = kinematic viscosity at 40°C of an oil of 0 viscosity index having the same kinematic viscosity at 100°C as the oil whose viscosity index is to be calculated, mm2/s (cSt),
Y = kinematic viscosity at 100°C of the oil whose viscosity index is to be calculated, mm2/s (cSt), and
H = kinematic viscosity at 40°C of an oil of 100 viscosity index having the same kinematic viscosity at 100°C as the oil whose viscosity index is to be calculated mm2/s (cSt).
5.1.3 Calculate the viscosity index, VI, of the oil as follows:
VI = [(L - U)/(L - H)] x 100
where:
U = kinematic viscosity at 40°C of the oil whose viscosity index is to be calculated mm2/s (cSt).
5.1.4 Calculation Example:
Measured kinematic viscosity at 40°C of the oil whose viscosity index is to be calculated = 73.30 mm 2/s (cSt)
kinematic viscosity at 100°C of the oil whose viscosity index is to be calculated = 8.86 mm 2/s (cSt)
From Table 1 (by interpolation) L = 119.94
From Table 1 (by interpolation) H = 69.48
Substituting in Eq 3 and rounding to the nearest whole number:
VI = [(119.94 - 73.30)/(119.94 - 69.48)] x 100 = 92.43
VI = 92
5.2 ASTM DS 39b Viscosity Index Tables for Celsius Temperatures is based on the above calculation and may be used instead of 5.1 - 5.1.4.
