Abstract: A heat exchanger for insertion in a tank which forms part of a vehicle cooler, has a plurality of stacked, flat tubes which consist of a first and a second tube half provided each with one circumferential edge flange, said flanges scalingly engaging with one another and forming a lap joint, and which have at each end a hole to establish communication between the tubes and to form an inlet chamber and an outlet chamber for the fluid to be cooled. The lap joint extends in the direction of the tube thickness in order to form a tube, the inner width of which differs from the outer width by the formulab.sub.i =b.sub.y -4twhereinb.sub.i =the inner width of the tube,b.sub.y =the outer width of the tube, andt=the thickness of the edge flange.