A heat exchanger, including first and second collecting tanks with an inlet, an outlet, and an opening through a wall of the first tank. At least one row of tubes extends between the collecting tanks, and the tubes and tanks carry a first medium and a second medium flows through the spaces between the tubes. A first partition divides the first collecting tank and defines an opening therethrough, and a second partition divides the second collecting tank, with the first and second partitions defining separate loops for the first medium when the first partition opening is closed. A discharge device selectively either simultaneously opens both the first collecting tank opening and the first partition opening for emptying or simultaneously closes both the first collecting tank opening and the first partition opening for operation.