With the continuous rise of energy conservation and environmental protection standards, optimizing the high temperature cleaning performance of lubricating oil and reducing engine piston deposits have become a top priority in the field of lubricating oil. In this study, the heat pipe oxidation test was adopted to conduct oxidation deposit tests on ethylene?propylene copolymer （OCP?type viscosity index improver）at 250, 280, and 310 ℃ respectively. Characterization of the wall deposits was performed using Fourier Transform Infrared Spectroscopy （FT?IR）, Scanning Electron Microscopy/Energy Dispersive Spectroscopy （SEM/EDS）, and 1H Nuclear Magnetic Resonance （1H?NMR） to analyze their morphological features, elemental composition, and functional group structures. The results indicate that at a temperature of 250 ℃, the deposit contents of the base oil and the mixed sample (1% mass fraction of OCP?type viscosity index improver + 99% mass fraction of base oil) were relatively close. The deposit amount of the mixed sample was greater than that of the base oil at 280 ℃, and the contents of C and S elements increased in this deposit, while the content of O element decreased. Due to the synergistic effect between the OCP and the base oil, the changes in hydrocarbons and oxygen?containing functional groups in the deposits of the mixed sample were reduced at 310 ℃, and sulfides escaped in the form of SO?, leading to a decrease in S element content.
