A heat exchanger manifold with improved sealing between the tank and header. The manifold includes a plastic heat exchanger tank having an opening for mating with a header and a lip extending substantially around a periphery of the opening. The lip has an outer surface and an upper surface extending outward of the tank opening, and a ridge extending upward from a portion of the upper surface extending substantially around the tank. The manifold further includes an aluminum heat exchanger header adapted to connect to a heat exchanger core. The header has a groove around the periphery thereof receiving the tank lip and a plurality of plastically deformable tabs extending from an edge of the groove. The tabs are bent inward and contact the ridge on the tank lip to secure the tank to the header.