TECHNOLOGY FOCUS - ELECTRICAL POWER AND ENERGY - Preferred Components: The fuel-cell power plant includes a water-immiscible fluid reservoir (94) connected with the radiator and direct-contact heat exchanger for supplying the water-immiscible fluid to the radiator loop and coolant loop; an operational control valve for selectively directing the water coolant within the direct-contact heat exchanger to flow out of the water region of heat exchanger into the coolant loop and for selectively directing the water-immiscible fluid to flow out of the separation region of heat exchanger into the radiator loop; a by-pass coolant passage (58) connected with the direct-contact heat exchanger and accumulator for directing the water coolant or water-immiscible fluid to by-pass the heat exchanger; an accumulator feed valve (48) connected with the coolant loop for selectively directing the water-immiscible fluid or water coolant within the coolant loop to flow into either a water inlet (30) of the accumulator or a water-immiscible fluid inlet (42) of the accumulator; an accumulator discharge valve (50) connected with the coolant loop for selectively directing flow of the water coolant from the accumulator into the coolant loop through an accumulator water outlet (32), or flow of the water-immiscible fluid from the accumulator into the coolant loop through an accumulator water-immiscible fluid outlet (34) or an accumulator water-immiscible fluid discharge header (40); and a direct-contact heat exchanger feed valve (54) connected with the coolant loop for selectively directing the water-immiscible fluid or the water coolant to flow into a mixing inlet of the direct-contact heat exchanger or to by-pass the direct-contact heat exchanger. The accumulator includes a porous layer (28) separating a water region (26) from a water-immiscible region (24).Preferred Method: The method includes shutting down the power plant by directing the water coolant to by-pass the direct-contact heat exchanger and flow from the accumulator into the coolant inlet of the fuel cell, directing water-immiscible fluid to flow from the accumulator into the coolant loop and fuel cell to displace the water coolant from the fuel cell into the accumulator, and directing water-immiscible fluid from the direct-contact heat exchanger into the fuel cell and coolant loop; and starting up the plant in sub-freezing ambient conditions by passing reactant streams through the fuel cell to generate heat, directing flow of water-immiscible fluid from the accumulator through the fuel cell to heat the fluid, directing the heated water-immiscible fluid to flow into the accumulator to melt frozen water coolant within the accumulator, directing the water-immiscible fluid to flow from the fuel cell into the direct-contact heat exchanger and into the radiator loop after the water coolant is melted, circulating the melted water coolant from the accumulator through the direct-contact heat exchanger and back into the accumulator, and circulating the water-immiscible fluid from the radiator loop through the direct-contact heat exchanger and radiator.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Fluid: The water-immiscible fluid may be perfluorocarbon and/or hydrofluoroether; or greater than or equal to6C alkane, alkene, and/or alkyne.    TECHNOLOGY FOCUS - POLYMERS - Preferred Fluid: The water-immiscible fluid is silicone, silicone copolymer, substituted silicone, siloxane, polysiloxane, and/or substituted siloxane or polysiloxane.Preferred Properties: The water-immiscible fluid has a freezing temperature of less than or equal to-20degreesC, a surface tension of less than or equal to35 (preferably less than or equal to20) dynes/cm, and a solubility in water of less than 0.1%.