Originally Posted By: BobFout
Dnewton, the Evolution section here explains it.
http://www.machinerylubrication.com/Read/533/base-oil-trends
Googling for group III+ also nets some more info.
My apologies; wasn't trying to pick on you; not my intent.
It's just that, like I said, there is no "pure" oil; they all exist with some secondary base stocks and varying additive packages. No one ever dares to refer to Mobil 1 as a "Group IV-" just because it has some lower base stocks in it to help carry the additives. Mobil 1 is not PURE PAO, but we all consider it group IV. It's a manipulated oil product just like T6, Edge, Synpower, and everything else.
Is a group III+ the "same" as a group IV-? We've heard of group II+, but would that be much different than a group III-? Are we splitting hairs so thin? Are we even concerned about the percentage of each base stock used? What makes something a "PAO" when it may have 51% group IV, but if it only had 48% group IV, what would it then be called?
Conceptually, it's like debating the merrits of a "C+" versus a "B-". The distinction is there, but it's so whacked and overblown because the you also have to include the sub-topics to give it frame of reference.
The reality is that marketing folks will never want well defined descriptions with % content on their product labeling; that would make it too easy to know what you're buying ...
I makes litte sense to keep sub-dividing the subdivisions ... Perhaps it's time for the lube industry to redefine the entire class description system.