The increasing importance of reducing greenhouse gas emissions and the ongoing evolution of vehicle-to-vehicle connectivity technologies have generated significant interest in platooning for commercial vehicles, where two or more vehicles travel in same traffic lane in relatively close proximity. This paper examines the effect of platooning on four increasingly aerodynamic tractor-trailer configurations, using a Lattice Boltzmann based CFD solver. Each platoon consisted of three identical tractor-trailer configurations traveling in the same lane at 65mph. Two different vehicle to vehicle gaps were studied, 5m and 9m, in addition to singleton (solitary) vehicles, representing an effectively infinite gap. Aerodynamic drag for the lead, middle, and trailing vehicle in the platooning configurations were compared to the corresponding single vehicle tractor-trailer configuration. Unlike similar investigations on platooning that solely focused on the potential fuel economy gain via aerodynamic drag reduction, this paper also highlights the adverse impact of platooning on the engine cooling performance in trailing vehicles, due to the reduction in ram air cooling caused by wake of the upstream vehicle. Since much of the fuel economy gain from aerodynamics could be at risk if the fan has to be engaged to meet engine cooling demand, this analysis should be an essential part of the cost-benefit consideration of platooning in the context of reducing fuel consumption and thereby, greenhouse gas emissions.