The thermal test chambers available at TARDEC for validation and development testing are different in terms of capability, size, and flow setup. The effects of the chamber setup on propulsion cooling airflow and the challenges of using thermal chamber tests to correlate CFD results and predict off-road performance will be discussed. Numerical simulation and test results for both a tracked combat vehicle tested in a large test cell and a wheeled MRAP vehicle tested in a smaller test cell will be presented. Numerical simulation results for these two different vehicles in on-road type of scenario and test chamber scenario at full-load cooling will be compared and contrasted. Results from CFD simulation with test cell set-up will be compared with actual physical testing in the test chamber. Procedures used for the propulsion cooling CFD simulation, best practices, limitations, and recommended procedure will be presented in detail.