A heat exchanger assembly includes first and second tanks having tube side walls, reservoirs formed therein, and apertures extending through the tube side walls. A flow tube having a plurality of fins on an exterior surface thereof, a first end, and a second end, the first end being received in an aperture of the first tank. A first seal is positioned between the flow tube and the first aperture. A retainer is positioned between the flow tube and the first aperture and between the first seal and the fins on the tube. A mounting block is positioned between the first tank and the fins on the tube, and is secured to the first tank. A second seal is positioned between the flow tube and the second aperture.