Originally Posted by M45
I guess to get the API icon on your oil you have to pay for the tests as well but not having it there doesn't mean you wouldn't pass the tests. kind of like organic food. sometimes it's just not worth the certification process.
do you have any information on why signature series didn't get the API cert?
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.