http://www.ftc.gov/opa/2001/02/zmax1.shtm
"The agency alleges that enhanced performance claims for the product are unsubstantiated, that tests cited to support performance claims actually demonstrated that motor oil treated with zMax produced more than twice as much bearing corrosion than motor oil alone, and that the three different products - an engine additive, a fuel line additive and a transmission additive - were all actually tinted mineral oil. "