The BITOG chart I was looking at was this:
Putting the simple back into Viscosity.
ASTM D2270
Calculating Viscosity Index from Kinematic Viscosity at 40°C and 100°C
The viscosity index (VI) is an arbitrary measure of the variation in the kinematic viscosity of a petroleum product due to changes in temperature between 40°C and 100°C. For example, a higher viscosity index indicates that the kinematic viscosity of the lubricant will decrease very little when the temperature is increased. The VI is simply reported as a numerical value that has no units. (9)
I was expecting a non-linear like a post but another person said how can two data points give a curve (straight or not) which leads to my other question is how can two oils have similar end points and have diff VI unless they have non-linear relationships. I would expect depending on VI improvers they would not all react to temperature the same.
I was just comparing and for a simple ratio I could not do the math. The MC is the odd one here with a much higher VI.
John Deere Turf Gard 10w30
100 C 10.9
40 C 65.5
VI 138
Pennzoil Conventional 10w30
100 C 10.5
40 C 69.5
VI 138
Pennzoil Gold 10w30
100 C 10.53
40 C 69.7
VI 135
Motorcraft 10w30 semi-syn
100 C 10.4
40 C 69
VI 159
Of course, in looking at other threads before I posted, there is the debate on whether high VI is really meaningful measurement.
I used the VI calculator at Widman's and not all match from the published specs from the supplier's web site.
