This study presents a comprehensive, transient, 3-D Computational Fluid Dynamics (CFD) model of a multi-cylinder flat engine's lubrication system, simulated using Simerics-MP+. Engine lubrication system is crucial for reducing friction, cooling, and cleaning engine components. Understanding its performance is essential for optimal engine operation. The model was applied to the lubrication system of a 4-cylinder, reciprocating internal combustion engine. The computational domain includes the positive displacement gerotor pump, pressure regulation valve, bearings, piston cooling jets, oil cooler, oil filter, and other relevant components. The gerotor pump and gallery bearings were modeled using real 3-D geometries without any assumptions. Bearing deformation and orbiting due to force imbalance were prescribed in the simulations. The simulation was conducted at 5000 rpm of engine speed. The simulated flow pressure distributions closely matched experimental data.