Viscosity index at 40 and 100 degree C?

why kinematic viscosity of oil(fuel or lubricating oil) is measured at 40 and 100 degree C.Is there any particular reason for measuring at these specific temperatures.Please explain as I already have read,at 100 degree C temperature the kinematic viscosity of standard oils are same but not able to understand what was the meaning of the statement.

Viscosity index at 40 and 100 degree C?
Viscocity and temperature relationship is exponential function


WHEN PLOTTED ON SEMI LOG PAPER THE GRAPH IS STRAIGHT LINE for all oils. To draw a viscocity vs temperature curve on semilog paper , the value of viscocity of the oil at two temperature are needed. Hence viscocity measurement at only two temperature is adequate . These two temperatures may be 40 and 100 deg. C as normal oil storage tank or maximum ambient temperature is around 40 deg. c and oil temperature rise of 60 deg.c is normally accepted values in running bearings or for mechanical atomisation of fuel oil under pressure.


kinematic viscocity = absolute viscocity/ densiity .


Putting actual values of a few standard oil at 100 geg. c you may check validity of what you have heard.
Reply:You want to check for the linearity of the curve of viscosity. You don't want the oil to be too viscous at a low temperature, and too low at high temperatures. Also, you want a linear curve that is as flat as possible, or as little a change from desired viscosity as temperature changes. Most fluids however are non-newtonian, and display a nonlinear viscosity index.
Reply:LOOK AT YOUR ASTM METHOD D-445-04,MANY PETRO PRODUCTS AND SOME NON-PETRO MATERIALS ARE USED AS LUBRICANTS AND THE CORRECT OPERATION OF THE EQUIPMENT DEPENDS UPON THE APPROPRIATE VIS OF THE LIQUID BEING USED FOR OPTIMUM STORAGE ,HANDLING, AND OPERATIONAL CONDITIONS.ALSO YOU MEASURE TO SEE IF YOUR CLIENT NEEDS TO BE IN SPEC FOR 180 OR 380.