Brian Whatcott wrote:

I can always learn something new about oil.
Then I saw their definition of viscosity index as ability to maintain
viscosity over a wide range of temperatures.

That was enough for me.
Forget it.

???

You must have read something Jax wrote. The quote below is directly cut
and pasted from the site ... it is about as accurate a definition as you
will find anywhere.

"The viscosity index of an oil is a measure of its tendency to change
viscosity with temperature changes. The higher the viscosity index (VI)
the more consistent an oil's viscosity is with temperature changes."

Rick