A fuel cell thermal management system (10) is provided for maintaining a fuel cell stack (12) within a desired operating temperature range. The system (10) includes a thermal storage reservoir (14), a radiator (16), and a mixing valve (18). Heat from the fuel cell stack (12) is rejected to the thermal storage reservoir (14), and heat from the reservoir (14) is rejected to ambient in the radiator (16). The mixing valve (18) receives a coolant flow from the fuel cell stack (12) at a first temperature T1 and a coolant flow from the radiator (16) or the reservoir (14) at a second temperature T2 and mixes the two coolant flow together to provide a mixed coolant flow to the stack (12) at a third temperature T3 to maintain the stack (12) within its desired operating temperature range.