Coolant conditioning unit for coolant of an internal combustion engine. The unit includes a cup-shaped housing, a removable cover for closing the housing, a replaceable filter insert arranged in the housing and being detachably connected to the cover, an inlet, an anti-drain valve that is normally open during filtering, and a stop valve arranged in the inlet. The stop valve is held in an open position by the filter insert and closes when the filter insert is removed from the housing and closes before the cover has been completely separated from the housing. This abstract is not intended to define the invention disclosed in the specification, nor intended to limit the scope of the invention in any way.