Increased quantities of fuel in the lubricating oil of CI engines pose a major challenge to the automotive industry in terms of controlling the oil aging and the wear caused by dilution. Due to a lack of methods to calculate the oil-fuel-composite transport across the ring pack, predicting the fuel ratio in the oil sump has been an extremely challenging task for engine manufacturers. An accurate and computationally efficient simulation model is critical to predict the quantity of fuel diluted in the oil in the preliminary development stage of automotive engines.In this work, the complex composite transport across the piston ring pack was reduced to a simple transport model, which was successfully implemented into a multi-body simulation of the ring pack. The calculation domain was partitioned into two parts, the ring grooves and the piston lands. Inside the grooves the oil flow caused by the pumping and squeezing action of the piston rings was calculated using the Reynolds equation. On the piston lands simplified Navier-Stokes equations were used to calculate the oil flow caused by the inertia force and dragging action of the blow-by gases.This reduced model enables a calculation of the composite transport in a minimum of time and is therefore well suited for DoE. The main oil flow was observed to be driven by the dragging action of the blow-by gases. The computed integral volume of fuel leaking into the oil sump was successfully validated against the measured value of accompanying experiments.