Upfront in a vehicle program, sizing of front end cooling module i.e. Condenser Radiator Fan Module (CRFM) and front grille opening is vital hence simulation tools like 1D have gained tremendous importance. This paper focuses on the modeling and analyzing performance behavior of engine cooling system using 1D simulation tool and also discusses the correlation of simulated results with test results. 1D model of engine cooling system is developed by inputting all necessary geometrical and performance data of all components (radiator heat load, coolant pipe geometry, CRFM, pump, thermostat etc.) with necessary assumptions. Air flow rates used on heat exchangers are predicted in 3D Computation Fluid Dynamics (CFD) analysis.First isothermal coolant circuit is modeled and coolant flow correlation is achieved to build confidence in modeling. Thereafter various changes in pipe dimensions and in other components were recommended to achieve desired coolant flow through respective branches of the coolant circuit. The correlation achieved between simulated result and a measured result is encouraging and as close as 5-8%. 1D engine cooling simulation is performed for various sign off test condition and Air - to - Boil (ATB) temperatures are predicted. The correlation achieved between simulated result and a measured result is encouraging and as close as 5%. This degree of correlation gave us confidence to evaluate different CRFM configurations for getting desired performance which in turns reduces iterative vehicle level tests.