The Relative Wear Performance of Neutral and Basic Zinc Dithiophosphates in Engines©

Abstract

Over the years, many bench tests have been used to guide synthetic organic chemists in their quest for new molecules to prevent valve train wear. Which bench tests to choose has always been an important issue, especially when the goal is to prevent valve train wear in an internal combustion engine, a very complicated system. Essential antiwear additives in modern engine oils are zinc dithiophosphates (ZnDTPs) and, although these materials have been used extensively, the fundamental mechanisms of their chemistries are not that well understood. In this paper, several nontraditional bench tests have been evaluated, some involving surfaces but no rubbing, and others lacking rubbing surfaces entirely. Despite these apparent deficiencies, these nontraditional chemistry-based tests all could be interpreted to predict a wear advantage for the neutral ZnDTP species relative to the basic ZnDTP species. This paper reports on engine tests of a neutral commercial-like ZnDTP and a basic commercial-like ZnDTP, with the result supporting the interpretation of the nontraditional bench tests: the neutral ZnDTP is better than the basic ZnDTP in engines with respect to valve train wear performance, with high statistical significance. Fundamental understanding of the chemistry of neutral and basic ZdTP has been shown to yield a practical result. Presented at the 53rd Annual Meeting in Detroit, Michigan May 17–21, 1998