This paper focuses on the fuel contribution to crankcase engine oil degradation in gasoline fueled engines in view of insoluble formation. The polymerization of degraded fuel is responsible for the formation of insoluble which is considered as a possible cause of low temperature sludge in severe vehicle operating conditions. The main objective of the study is to understand the mechanism of formation of partially oxidized compounds from fuel during the combustion process, before their accumulation in the crankcase oil. A numerical method has been established to calculate the formation of partially oxidized compounds in spark ignition engines directly, by using 3D CFD. To further enable the possibility of running a large number of simulations with a realistic turn-around time, a coupled approach of 3D CFD (with simplified chemical mechanism) and 0D Kinetics (with full chemical mechanism) is proposed here. Information such as pressure, air-fuel ratio, temperature at the time when the flame approaches the wall is extracted from 3D CFD and is applied as initial condition in the detailed analysis of 0D Closed Homogeneous Reactor(CHR) model for the formation of partially oxidized compounds. By using this approach, spatial variation around the combustion chamber can be easily evaluated by sweeping parameters such as pressure, temperature and equivalence ratio, etc. in 0D chemical kinetic calculations.