ZDDP and engine break-in history

"...by 1958, as reported by Larson; The compound type zinc dialkyl dithiophosphate has gained wide acceptance in the United States for high quality motor oils. Two out of three of the major United States automobile manufacturers either require zinc dithiophosphate at about 1 % of an 80% concentrate in the initial fill in new automobiles or require qualification tests which only zinc dithiophosphate can pass."'

This quote speaks volumes about OEM (Original Equipment Manufacturer) car companies conclusions 50 years ago regarding the use of ZDDP in the initial fill oil, but what is the situation today? We have analyzed the break-in oil supplied with numerous major manufacturers, and found contrary to the OEMs' claims that ZDDP is now much less necessary than it was historically, many break-in oils installed at the factory are loaded with ZDDP. Specifically the higherperformance engines of today seem to be filled at the factory with a high level of ZDDP. This indicates that in the viewpoint of OEMs, the inclusion of ZDDP is still mandatory for high-performance engine break-in.
ZDDP was originally blended into engine oils as a potent anti-corrosive and anti-oxidative additive. Early fuels were high in sulfur, and the resulting blow-by from combustion contributed a large amount of sulfuric acid and moisture to the oil. ZDDP eliminated much of the corrosion problem which had plagued the automotive industry up to that point. An additional problem with early oils was the rapid oxidation of the highly unsaturated base oils, but fortunately ZDDP displays a strong antioxidant action. Improved oil refining and a move to base oils consisting of more highly hydrogen saturated molecules would eventually reduce but not eliminate the base oil oxidation problem. By the 1940s and the advent of higher-power engines, it was observed that oils with ZDDP would also greatly prolong the life of high-wear components, such as the cam and lifter.
These highly beneficial characteristics of ZDDP have resulted in the incorporation of ZDDP in virtually all automotive engine oils for the last 70 years. The fact that the one economical additive can perform triple duty has ensured its continued use.
The recent catalytic converter life mandate by the EPA has led to declining ZDDP levels in most API rated oils. In order to replace the functionality of the ZDDP, additions are now made to the additive package to control corrosion and serve as antioxidants. In order to deal with the lower antiwear agent concentration, a few approaches have been taken to ensure new car compatibility: substitution of roller cam followers for flat cam followers, and the addition of different
anti-wear agents, such as boron to augment the lowered ZDDP level in the oil. Unfortunately, since part of the remedy for the reduced ZDDP levels was the redesign of new engines, the newer oils no longer represent a complete lubrication package for older high-performance and classic engines, especially during break-in.

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