Method and control unit for operating a diesel internal combustion engine or a dual-fuel internal combustion engine operated in the diesel mode

A control unit configured to operate a diesel internal combustion engine or a dual-fuel internal combustion engine operated in a diesel operating mode, wherein the control unit is configured to:

• receive, from a sensor, a measurement value of a total base number and/or receive from a sensor a measurement value of a viscosity of lubricating oil currently used for lubricating the internal combustion engine in an oil circuit;
• determine an exchange oil quantity based at least in part on the measurement value of the total base number and/or the measurement value of the viscosity;
• emit a control signal, as a function of which, a first valve is opened and currently used lubricating oil is removed directly into a collection tank from the oil circuit to an extent corresponding to the determined exchange oil quantity;
• and
• emit a control signal as a function of which a first valve is opened and new lubricating oil to an extent corresponding to the determined exchange oil quantity is suppliable to the oil circuit directly from an oil storage tank.