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. 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 critical 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 independence 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.