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

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.