Abstract: A heat exchanger includes first and second circuits disposed in a counterflow configuration for respectively channeling first and second fluids. In one embodiment, the first circuit is joined to an aircraft engine fuel tank with the first fluid or fuel being a heat sink, and the second circuit is joined to a plurality of aircraft engine oil sumps, with the second fluid or oil being cooled in the heat exchanger by the fuel. The second circuit of the heat exchanger includes first and second outlets in succession with a portion of the oil being removed prior to completion of flow through the heat exchanger and channeled to one or more of the sumps. The remaining portion of the oil in the heat exchanger is removed after completion of flow therethrough at a lower temperature than that of the first portion and is channeled to a predetermined one of the sumps for providing cooler oil thereto.