The relative oxidation inhibition performance of some neutral and basic zinc dithiophosphate salts

Recent engine testing on separate neutral and basic zinc dithiophosphates ( ZnDTPs) showed a difference in valve train, wear performance, with the neut ral ZnDTP giving statistically better wear inhibition in Sequence VE tests. Since the literature was lacking on the oxidation inhibition performance o f the separate neutral and basic salts, Me systematically examined the rela tive antioxidancy of several neutral and basic ZnDTP salts in various formu lations. The results were dependent on the type of base oil and formulation used and the presence of other additives. P-31 NMR Spectroscopy: coupled w ith Oxidator Bench Test studies, were used to reach these conclusions.