The Effect of Engine Operating Temperature on Valve Train Wear: Mechanistic Understanding Through Used Oil Analysis

Abstract

Analysis of used oils from a series of Peugeot TU-3 engine tests has been performed to investigate the effect of engine operating temperature on valve train wear in this engine. Iron content of intermediate and end-of-test used oil samples has been used as a monitor of valve train wear during the test and has indicated that a significant proportion of the wear occurs during the initial low-temperature phase of the test. Analysis of used oils using 31phosphorus nuclear magnetic resonance spectroscopy (3lP NMR) suggests that this is associated with low rates of zinc dialkyldithiophosphate (ZDTP) degradation during low-temperature operation, resulting in levels of extreme-pressure (e.p.)/anti-wear materials which are insufficient to provide the necessary wear protection. Modification of the TU-3 test procedure, such that the high operating temperature phase precedes the low-temperature phase, results in very much lower observed levels of valve train wear.31 P NMR analysis indicates that this is associated with a much more rapid buildup of active ZDTP degradation products during initial high-temperature operation, which can then provide the necessary anti-wear protection during subsequent low-temperature operation.