A conjugate heat transfer study was undertaken using STAR-CD. The boundary conditions are given by vehicle operation and engine operation. All three mechanisms of heat transfer, i.e., convection, conduction, and radiation, were included in the analysis. The vehicle exhaust system components temperatures were analysized at certain several separate variables such as the velocity and temperature of the exhaust gases which depend on the engine operation conditions and the velocity and temperature of the external airflows which depend on vehicle operations. The results showed all three mechanisms of heat transfer and increased quantitative understanding of the flow conditions surrounding vehicle exhaust system.