The present work deals with the 3-D, transient, system level CFD simulation of an automotive coolant system using a 3D CFD solver Simerics MP+®. The system includes actual CAD of radiator, cooling jacket, coolant pump, bypass valve and thermostat valve. This work is in continuation of the work done by Srinivasan et al. [1] where wax melting, conjugate heat transfer, Fluid Structure Interaction (FSI) of the valve had been solved. Thermostat valve was controlled by wax phase change model which also incorporates the hysteresis effect of wax melting and solidification. The previous work dealt with the simulation of complete cycle, opening, and closing of the thermostat valve system. Besides the physics considered in the previous study, the current model also includes the treatment of cavitation to account for the presence of dissolved gases and vaporization of the liquid coolant. A methodology has been developed and implemented where the run-time of such a system has been made considerably faster to be able to simulate complete drive cycle tests. The distributed parallel solver of Simerics-MP+, coupled with the newly developed method made it to successfully simulate an HOUR of drive-cycle of coolant system within a day of simulation time. Various parameters from experimental measurements have been corroborated with the simulation results to validate the developed technology. Further, a few design iterations are performed to showcase the potential of the developed methodology.