The high fuel dilution in engine oil causes oil viscosity reduction and it is a serious impact on engine wear by oil lubricative degradation. This paper describes the study of engine wear status trough understanding for engine oil degradation degrees and uses one 2.0 liters diesel engine and one vehicle with 2.0 liters diesel engine for these tests. To measure reliable fuel dilution, GC-SIMDIS was used. And to the elements analysis, Spectrometer was used. Also, Engine oil sample test was performed on both the manufactured new engine oil samples for base data set-up and used oil samples from engine bench and fleet vehicle.