NOVELTY - A freeze-tolerant fuel cell power plant comprises fuel cell(s) having coolant inlet and coolant outlet; a coolant loop including a freeze-tolerant accumulator for storing and separating water-immiscible fluid and water coolant, a direct-contact heat exchanger, and a coolant circulating pump for circulating the water-immiscible fluid and water coolant; and a radiator loop including a radiator and a radiator pump.    USE - The fuel cell power plant is used for generating electrical current from hydrogen-containing reducing fluid fuel and oxygen-containing oxidant reactant streams. It is useful in transportation vehicle, or as portable power plant or stationary power plant.    ADVANTAGE - The use of direct-contact heat exchanger with a water coolant and water-immiscible fluid minimizes volume of water coolant necessary to cool an internal combustion engine and minimizes exposure of a coolant system (such as engine) to antifreeze conditions.    DETAILED DESCRIPTION - A freeze-tolerant fuel cell power plant comprises fuel cell(s) (12), a coolant loop (18), and a radiator loop (84). The fuel cell includes a coolant inlet (14) and a coolant outlet (16) for directing a water-immiscible fluid and a water coolant to flow through the fuel cell. The coolant loop includes a freeze-tolerant accumulator (22) connected with the fuel-cell coolant outlet for storing and separating the water-immiscible fluid and water coolant, a direct-contact heat exchanger (56) connected with the accumulator and the fuel-cell coolant inlet, and a coolant circulating pump (21) connected with a coolant passage (20) for circulating the water-immiscible fluid and water coolant through the coolant loop. The radiator loop includes a radiator (86) secured between a water-immiscible fluid discharge and a water-immiscible fluid inlet of the direct-contact heat exchanger for removing heat from the water-immiscible fluid, and a radiator pump (92) secured to the radiator loop for circulating the water-immiscible fluid through the radiator and direct-contact heat exchanger.    INDEPENDENT CLAIMS are also included for the following    (A) a method of operating a freeze-tolerant fuel cell power plant by securing a direct-contact heat exchanger with the accumulator and fuel-cell coolant inlet, providing a radiator loop, mixing water coolant with water-immiscible fluid within a mixing region of the direct-contact heat exchanger; and separating the water coolant within the direct-contact heat exchanger so that the water coolant flows out of a water region of the heat exchanger into the coolant loop and the water-immiscible fluid flows out of the separation region into the radiator loop; and    (B) a direct-contact heat exchanger for removing heat from water coolant, comprising a water coolant inlet (70) secured to a mixing region (72) for directing heated water into the mixing region, a water-immiscible fluid inlet (90) secured to the mixing region for directing a water-immiscible fluid into the mixing region, a water-immiscible fluid discharge (91) secured to a separation region (74) that is connected with the mixing region, and a water coolant outlet (85) secured to a water region (76) that is connected with the separation region so that the water-immiscible fluid mixes with the heated water coolant within the mixing region, removing heat from the water coolant.    DESCRIPTION OF DRAWING(S) - The figure is a schematic representation of the inventive freeze-tolerant fuel cell power plant.    Fuel cell (12)    Coolant inlet (14)    Coolant outlet (16)    Coolant loop (18)    Coolant passage (20)    Coolant circulating pump (21)    Accumulator (22)    Water-immiscible region (24)    Water region (26)    Porous layer (28)    Water inlet (30)    Water outlet (32)    Water-immiscible fluid outlet (34)    Water-immiscible fluid discharge header (40)    Water-immiscible fluid inlet (42)    Accumulator feed valve (48)    Accumulator discharge valve (50)    Heat-exchanger feed valve (54)    Direct-contact heat exchanger (56)    By-pass coolant passage (58)    Water coolant inlet (70)    Mixing region (72)    Separation region (74)    Water region (76)    Radiator loop (84)    Water coolant outlet (85)    Radiator (86)    Water-immiscible fluid inlet (90)    Water-immiscible fluid discharge (91)    Radiator pump (92)    Water-immiscible fluid reservoir (94)