After 70+ years of trouble-free, metal-to-metal engine protection, the E.P.A. is forcing ZDDP (Zinc Dialkyl-Dithio-Phosphate = Zinc and Phoshorus) from domestic motor oil. If your engine was designed prior to the 1990s, the non-roller lifters require ZDDP in the motor oil to avoid premature deterioration. Don’t let the lifters run metal-to-metal. Keep ZDDP, via ZDDPlus™, in your motor oil. Add the 4 fluid ounce contents of a bottle of ZDDPlus™ at every 4- to 5-quart oil change. It’s the perfect solution for owners of classic and high-performance vehicles.