A fuel cell system, including a plurality of bipolar plate assemblies, each assembly including a first plate and a second plate with an internal coolant flow path disposed therebetween, a flow path for a first reactant gas on a side of the first plate opposite the internal coolant flow path, and a flow path for a second reactant gas on a side of the second plate opposite the internal coolant flow path, and a cooling system configured to place coolant in thermal communication with the plurality of bipolar plate assemblies, wherein cycling pressure differentials between the internal coolant flow path and the external reactant gas flow paths cause expansion and contraction of a volume of coolant disposed within the bipolar plate assembly, thereby pumping coolant through the cooling system. A method of cooling a fuel cell-powered vehicle is also provided.