The jet lubrication method is extensively used in the constant mesh high performance transmission system operating at range of speeds though it affects mechanical efficiency through spin power loss. The lubrication jet has a key role to maintain the meshing gears at non-fatal thermal equilibrium by effectively dissipating the heat generated to the surrounding. Heat Transfer coefficient (HTC) is the indicator of the thermal behavior of the system, which provides great insight of efficient lubrication system that needs to be employed for prescribed type of transmission. 1D and 3D simulations are of countless value in optimizing the automotive power train transmission system performance parameters. Thermal performance prediction of the jet lubricated transmission system through 3D CFD analysis is quite comprehensive task compared to 1D analysis. Both 1D and 3D methods complement each other to great extent in design process and one such exercise is demonstrated in the current activity. HTC on the transmission housing interiors and internal components from the simulation can be used later as look-up table in 1D computational methods. In this study, a segment of the transmission unit which constitutes a gear pair is used for the simulation. Parametric study is carried out by considering the crucial parameters affecting the thermal performance such as lubrication jet flow rate and rotational motions of the gears with speeds and temperatures. Multiphase CFD analysis with volume of fluid (VOF) approach and overset mesh motion method for rotational motion of the gears are used in Star CCM+. A grid independent study is done to choose the appropriate mesh distribution and to ensure the results are free from potential numerical errors. Physical phenomena such as oil sump formation, lube oil paddling, chaotic air motion and heat energy transfer, which make computational fluid dynamics methods quite complicated, were precisely captured. Heat transfer coefficient of the interior surfaces of the transmission housing, main gear surfaces and lay gear surfaces of the third gear pair as influence of jet flow and rotation is monitored and measured during the transient CFD simulation. Reported simulation results under typical operating scenarios enable designers to work towards better design of the transmission system.