I read it in an oil article that Amsoil use a lot of zinc and other anti-wear addicitives to make their oil superd. It is very good for the engine but bad for other part of the car. I just go by what the author said. It is a book on oil, so the source is trustworthy.

Many companies have oil additives that can kill engine because the additives are nothing but Teflon. Teflon is a DuPoint product and Dupoint said it is bad for the engine. DuPoint doesn't make the additive, it only sells the Teflon to companies to make it. Under the free trade law, Dupoint can't deny business to legitimate companies, so it must sell products even though it knows that the product can be harmful to engine.

I don't use additive because Mobil 1 is good enough. It is cheap to keep fresh oil in a car. A full tank of gas cost more than an oil change and I think people use more than a tank of gas a month. At least people driving their own cars anyway.