Abstract: An improved radiator assembly (10) that functions as a crossflow heat exchanger for use on liquid cooled engines. The assembly (10) uses fewer parts than conventional radiators and features a core assembly (11) comprised of a single vertical-row plurality of horizontally or vertically and alternately stacked radiator fins (11a) and radiator tubes (11b). With this core-stack design all the heat exchanging elements are located in a single frontal plane with the ram air applied normal to the plane. The radiator fin design also employs more fins-per-inch than conventional designs. Therefore, allowing a greater fin-to-tube contact which, in turn, provides a more effective heat transfer surface. The core stack is held under compression by inserting the ends of the radiator tubes (11b) into corresonding apertures located on the inward side of a cylindrical seamless outlet reservoir (10) and inlet reservoir (15).