Tiny,
I don't think anyone is full of BS. This is my uneducated explanation on this slippery subject.
We take an oil and measure its viscosity at zero degrees, and assign it a grade of 10 weight.
We take that same oil, heat it to 210 and measure its viscosity...wow, pretty thin. Maybe a 2 weight...way too thin for any automotive use.
We take that same oil and pump it full of viscosity index improver's and do the same test again.
It still flows as a 10 weight at zero, but when heated to 210, because of the goodies in it, it does not 'thin out' as much, or loose its viscosity. Now it measures as a 30 weight at 210 degrees.
This is a multigrade oil.
The parameters for determining viscosity at zero are not the same as those for determining the viscosity at 210 degrees.
As the oil is heated and tested, it doesn't get "thicker", it just doesn't thin out as much as a oil that has not been modified by the chemists.
STP is a VI improver in drag. When you are playing with your Zahn cup, be your own chemist and mix some of into your concoction...you might invent a new oil.
Stuart
