Cobblehillfarms

Older formulations of oils contain an additive called ZDDP (zinc dialkyl diphosphate) that controlled sliding friction. This was most useful in protecting lifters from galling due to extreme loads placed on the tappets. Roller valvetrains and OHC followers of today's cars do not require this additive. The idea was that ZDDP was degrading catalytic converter and oxygen sensor performance. Due to the fact that the are no domestic cars running these cams today, the feds stepped in and mandated that it be removed from the formula. This led to a rash of failed cams in the hot rod/drag racing community where flat tappets are quite the norm. Fortunately, this additive can still be found in Shell's Rotella Oils and other diesel oils. Look for the starburst symbol on the bottle. API ILSAC GF-4 energy saving oil is the first indication that your oil does not carry the ZDDP additive. To quote Hot Rod magazine... "Modern heavy duty truck diesel oil with lots of ZDDP will be marked Cl-4 and Cl-4 Plus. They also easily pass the API Service SL gasoline performance test, but due to the ZDDP content, not the SL chemical composition specs. Such truck oils are an economical and effective solution for flat tappet longevity, according to many sounces." Hot Rod June 2006

Hope this Helps

Let's go Mountaineers

Aaron