The current work investigates a method in 1D modeling of cooling systems including discretized cooling package with non-uniform boundary conditions.In a stacked cooling package the heat transfer through each heat exchanger depends on the mass flows and temperature fields. These are a result of complex three-dimensional phenomena, which take place in the under-hood and are highly non-uniform. A typical approach in 1D simulations is to assume these to be uniform, which reduces the authenticity of the simulation and calls for additional calibrations, normally done with input from test measurements.The presented work employs 3D CFD simulations of complete vehicle in STAR-CCM+ to perform a comprehensive study of mass-flow and thermal distribution over the inlet of the cooling package of a Volvo FM commercial vehicle in several steady-state operating points. The results from these are correlated with test readings and are imposed on a 1D model of the cooling stack with inlet discretization, which features non-uniform boundary conditions.The 1D model is tested in steady state and transient conditions. Results are correlated with readings from dynamometer tests.No major indications were present to support that the non-uniform approach improves accuracy of simulation. Nevertheless, the results show, that the suggested predictive method successfully captures the thermal effects of recirculation while reducing the necessity for calibrations done by prototype testing.