Originally Posted by oil_film_movies
Originally Posted by RamFan
My understanding is that VI has more to do with decreasing viscosity changes during low temperatures as opposed to high temperatures.
VII chemicals thicken a base-oil when hot. Hardly any effect at all when cold. For example, if you formulate a 0w30, you need to use thin base oils to get the "0w" rating, then you need to add VII to get the "30" rating. .... If you DIDN'T add any VII, then you might get something like a lighter-side "20" weight oil (kv100) hot.
My comment wasn't geared towards VII but the actual VI. I don't think I communicated that clearly in my original post. Say you have two 0w30 oils, one with a VI of 180 and one with a VI of 205. At operating temperature they will both have the viscosity of an Xw30. However the oil with the VI of 205 should maintain a viscosity that's closer to its operating viscosity in colder temps as compared to the oil that has a VI of 180, in theory at least.