Originally Posted by flyboy1100
i think because they sometimes change basestock providers and with the Group IV/V oils you can't do that w/o getting re-certified, also the Zinc content might be too high for the SN standards, but Amsoil does a lot of QC so I'm not worried.
one thing I have found when researching this today is that with Group I-III oils you can change basestocks w/o recertification, but with IV-V you can't. so the API does play favorites just a little to the oil that comes out of the ground.
I just read someone else saying this on a different forum.