Abstract: A method of estimating an operational aspect of an internal combustion engine is disclosed, wherein the engine comprises a crankcase enclosing at least part of a crankcase volume, a crankcase ventilation outlet connected to the crankcase volume, and a gas cleaning assembly comprising an oil separator unit and a pump unit configured to pump gas from the crankcase volume to the oil separator unit via the crankcase ventilation outlet. The method comprises the steps of obtaining data indicative of a pumping rate of gas pumped by the pump unit and estimating the flow rate of gas through the crankcase ventilation outlet based on the data. The present disclosure further relates to a computer program, a computer-readable medium, a control arrangement, an internal combustion engine, and a vehicle.