a plurality of stacked tubular members defining a first set of flow passages therethrough, the tubular members having a boss portion located at each end thereof, said boss portions defining respective inlet and outlet openings, the respective inlet and outlet openings of each of said stacked tubular members communicating to define inlet and outlet manifolds for the flow of a first fluid through the first set of flow passages, the tubular members having opposed peripheral flange portions joined together in the stacked tubular members to define a second set of flow passages between adjacent tubular members for the flow of a second fluid through the heat exchanger, the tubular members having transverse end wall portions defining a sealing surface;

a corrugated bypass tube located generally parallel to the plurality of stacked tubular members, the corrugated bypass tube being exposed to ambient air and having opposed end portions defining open ends for the flow of additional second fluid therethrough;

a pair of external end plates located respectively at the ends of the stacked tubular members and the corrugated bypass tube, each end plate having a peripheral wall defining a first opening for allowing said second fluid to flow through said second set of flow passages, the peripheral wall being sealingly attached to the transverse end wall portions of the plurality of stacked tubular members, and each end plate defining a second opening sealingly attached to one of the end portions of the corrugated bypass tube.