The present invention relates to a venting tank, suitable for being fitted in a cooling system of a motor vehicle and defining an inner space intended for receiving a coolant, the venting tank including at least one inlet and at least one outlet for the coolant which are arranged below a minimum liquid level when the vehicle is in service, wherein the venting tank also includes, opposite the inlet or at least some of the inlets, a member for guiding the coolant, penetrating into the inner space via the inlet, following a flow directed toward a lower wall of the venting tank opposite the flow arriving through the inlet, and forming a 180-degree arc. The invention also relates to a motor-vehicle cooling system provided with such a venting tank.