Abstract: A heat exchanger comprises an as-cast combined header and tank having a header portion integral with a tank portion. The cast header and tank combination has a plurality of openings originally cast in the header portion of the combination and at least one opening originally cast in the tank portion of the combination for passage of coolant into or out of the cast header and tank combination. Tubes are received in and extends through the header portion openings, and resilient grommets seal the tubes to the header portion to prevent leakage around the tubes. In making the heat exchanger, there is provided an inner mold section and outer mold section corresponding respectively to the interior and exterior configurations of a desired combined header and tank having a header portion integral with a tank portion.