Engine and transmission oil systems are commonly pressurized by gerotor style pumps, due to their simplistic design and low cost. Gerotor pumps are designed with certain tolerances of the gears and housing, thus creating a tradeoff of lower cost with larger tolerances and higher cost with smaller tolerances. By building a detailed gerotor pump model with a 1D hydraulic flow network, engineers can evaluate pump performance with these tolerances as input and compare to find the optimal design. This paper showcases the ease of building a gerotor model in 1D by using an automated process extracting the key model inputs directly from the pump CAD file. The gerotor pump performance is predicted including flow rate, total power loss, volumetric efficiency, and total efficiency vs. pump speed, pressure rise, clearance tolerances, and temperature, and compared with experiment. A predictive friction model for gerotor pumps is proposed and total torque required to drive the pump is compared directly with experiment. Additionally, an internal leakage model for predicting volumetric efficiency taking into account physical clearance between inner and outer gears, as well as temperature is discussed.