A fleet test study was initiated to compare the use of a unique boundary chemistry (UBC) containing PTFE engine treatment, as a supplement to a current 10W-30, API SJ/GF-2 motor oil, versus the use of the oil without any supplement. The test was conducted with a taxi fleet of 1998 Chrysler 2.4L minivans. The factory-fill oil was drained after 5 thousand km and the group of vehicles entered the test program designed as a double-blind study, wherein, neither the drivers nor analysts knew the identities of reference and treated engines.Half of the taxis received a one-time application of the engine treatment. Subsequent oil drain intervals were conducted every 6.5 thousand km so that at 11 thousand km a baseline and treated engine were pulled from the vans and sent to the laboratory for analysis. The rest of the fleet continued on to 50 thousand km, six oil changes later, when two more engines were obtained as before. The last data point was at the 82 thousand km mark.Wear metal analysis of the drain oils was performed at each oil drain interval. The camshaft lobes were photographed, measured and then sectioned to remove the nose and foot of representative specimens for surface analysis by x-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). This revealed the presence of PTFE surface features, in addition to, the formation of iron fluoride on components subjected to boundary lubrication conditions. These same tribochemical films and PTFE inclusions were still detectable at the high mileage accumulation points. This illustrated that a one-time, initial treatment of UBC displayed a carryover effect in terms of anti-wear film formation. Hypotheses and mechanisms are proposed to account for the analytical and physical observations.