NOVELTY - A reformate cooling system (10) comprises a first heat exchanger having first and second core portions (34, 36), and a second heat exchanger having third and fourth core portions (38, 40). The first core portion is located upstream from the second core portion with respect to both coolant and reformate flows. The third core portion is located upstream from the fourth core portion with respect to reformate flow. One of the third and fourth core portions is located upstream from the first core portion and the other is located downstream from the second core portion with respect to coolant flow.    USE - For use in fuel processing sub-system (12) for reducing level of carbon monoxide in reformate flow for a proton exchange membrane fuel cell system (16).    ADVANTAGE - The reformate cooling system does not require forward or backward bypassing of coolant flow and allows for a simplified control scheme within a fuel cell system, thus eliminating the need for coolant flow pumps and/or coolant flow control valves or bypass valves in comparison to conventional cooling systems.    DETAILED DESCRIPTION - A reformate cooling system comprises two heat exchangers to transfer heat from reformate flow to coolant flow. A first heat exchanger is located upstream from a first preferential oxidizer with respect to the reformate flow. The heat exchanger includes first and second core portions through which reformate and coolant flows pass in heat exchange relation to each other. The first core portion is located upstream from the second core portion with respect to both coolant and reformate flows. A second heat exchanger is located upstream from a second preferential oxidizer and downstream from the first preferential oxidizer with respect to the reformate flow. The second heat exchanger includes third and fourth core portions through which reformate and coolant flows pass in heat exchange relation. The third core portion is located upstream from the fourth core portion with respect to the reformate flow. One of the third and fourth core portions is located upstream from the first core portion and the other core portion is located downstream from the second core portion with respect to the coolant flow. Coolant flows in series through one of the third and fourth core portions, first core portion, second core portion and the other of third and fourth core portions. Reformate flows in series through the first core portion, second core portion, first preferential oxidizer, third core portion, fourth core portion and second preferential oxidizer.    DESCRIPTION OF DRAWING(S) - The figure is a diagrammatic representation of a reformate cooling system.    Reformate cooling system (10)    Fuel processing sub-system (12)    Proton exchange membrane fuel cell system (16)    Coolant flow path (30)    Reformate flow path (32)    First and second core portions (34, 36)    Third and fourth core portions (38, 40)