I had a question if the OTC dino oil I was using had a Group I or Group II base stock and I was told it was a blend of the two base stocks. Then I got this comment: "In order to meet ILSAC GF-3 specification, the low viscosity grades, 5W-20, 5W-30 and 10W-30, of our motor oils include Group II base stock in their formulation." From the reply is seems that the 10w-40, which is not GF-3, would therefore be only a Group I. What is it about the GF-3 specs that would make it necessary for them to use some Group II for blending in the 5w-20,5w-30,10w-30 but not in the 10w-40 grade? Can anyone figure this out?