by Robert Sanborn on Mon, Oct 15, 2007, who was a member of the STLE Society of Tribologists and Lubrication Engineers for 15 years.
ZDDP (Zinc Dithiophosphate)
In 2006 when a new motor oil warranty category for gasoline engines was developed GF-4, problems started occurring with older cars. When a new warranty specification is put on the market and licensed by the American Petroleum Institute (API) it makes all other previous specifications obsolete. All cars are supposed to be able to run on the new oil, however this is not the case with GF-4.
Zinc and the New Catalytic Converters
For many years major oil companies have used ZDDP (zinc dithiophosphate) in their motor oil formulations. The reason for this is ZDDP acts as a good anti-wear agent, and until metals of all kinds have escalated wildly in price, it was relatively cheap. Furthermore due to the skyrocketing price of platinum and palladium, Original Equipment Manufacturers (OEM) decided to change the composition of your vehicles catalytic converter. With the new catalytic converter material, the new GF-4 specification is fine for new vehicles, however cars with flat tappet engines are not so lucky. Due to the pressure on flat tappets the new additives in the GF-4 are not working and customers are reporting early failure in droves! This is not an isolated problem, and the oil companies were aware of this problem. What has happened is that the EPA has mandated that sulfur, phosphorus and zinc (sulfated ash) were to be removed from the oil as it destroys the catalytic converter over a long period of time.
Older cars have run into a myriad of problems with flat tappet camshafts. Premature failure seems to be the rule rather than the exception. Car owners are mad and want answers fast. The fact is that older cars with their different catalytic converters need a product like zinc to protect its critical parts.