Eastwood ZDDP Oil Additive has been designed to remove ZDDP(Zinc Dialkyl Dithio Phosphate) from all conventional and synthetic motor oils. If your engine was manufactured before 1989 the non-roller lifters require ZDDP to avoid premature deterioration. Eastwood ZDDP Oil Additive also alters bearing and journal surface characteristics to prevent metal to metal contact. Under extreme conditions like a high performance motor, ZDDP reduces the tendency of parts to scuff or gall under heavy loads. Eastwood ZDDP Oil Additive should be added to every 4-6 quart oil change. Which in return will give the added protection your motor needs.