TECHNOLOGY FOCUS - ELECTRICAL POWER AND ENERGY - Preferred Component: A two-component coolant mixing system is included. It comprises a coolant diversion valve (70) for directing the two component mixed coolant to flow from the coolant loop to the accumulator, a water immiscible fluid feed valve (72) secured in fluid communication between the coolant loop and the accumulator for directing flow of the water immiscible fluid from the accumulator into the coolant loop, a suction generating mechanism (74) secured in fluid communication between the coolant loop and the accumulator for applying a suction force to the accumulator for withdrawing the water component of the two-component fluid from the accumulator into the coolant loop, and a mixer (76) secured in fluid communication with the coolant loop for mixing the water component with the water immiscible fluid within the coolant loop. A mixing system by-pass valve (73) is secured in fluid communication with the coolant passage that directs the coolant from the coolant passage into the accumulator by-passing the mixing system (69). Fuel cells are cooperatively disposed in a fuel cell stack assembly. Porous water transport plates are secured in heat and mass exchange relationship with the fuel cells within the cell stack assembly. A high-volume coolant inlet manifold is defined within the cell stack assembly for directing flow of the two-component mixed coolant through the water transport plates into a coolant exhaust passage of the coolant loop. A coolant by-pass line is secured between the high-volume coolant inlet manifold and the coolant exhaust passage. The high-volume coolant inlet manifold is dimensioned to receive and direct to the coolant by-pass line a coolant flow rate that is at least five times a coolant flow rate of coolant flowing through the water transport plates from the high volume coolant inlet manifold to the coolant exhaust passage to enhance mixing of the two-component mixed coolant flowing through the cell stack assembly. An antifreeze coolant loop (54) is provided for circulating an antifreeze coolant through an antifreeze coolant passage (56), an antifreeze coolant pump (58), the coolant heat exchanger, and an antifreeze coolant radiator (60), for removing heat from the coolant heat exchanger and the antifreeze coolant. A heat-exchange by-pass valve (88) is secured in fluid communication with the coolant passage and with a heat-exchange by-pass line (90) for directing the coolant to by-pass the heat exchanger and flow back into the coolant passage.    TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Composition: The two-component mixed coolant contains 50-98, preferably 80-95 vol.% water immiscible fluid component and 2-50, preferably 5-20 vol.% water component. Preferred Property: The water immiscible fluid has a freezing temperature of less than or equal to 10degreesC and has a surface tension of less than or equal to 35 dynes/cm.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Composition: The two-component mixed coolant contains 50-98, preferably 80-95 vol.% water immiscible fluid component and 2-50, preferably 5-20 vol.% water component. Preferred Property: The water immiscible fluid has a freezing temperature of less than or equal to 10degreesC and has a surface tension of less than or equal to 35 dynes/cm.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Component: The water immiscible fluid is perfluorocarbons, and/or hydrofluoroethers. It is also alkanes, alkenes, and/or alkynes having greater than or equal to 6C.    TECHNOLOGY FOCUS - POLYMERS - Preferred Component: The water immiscible fluid is silicones, substituted silicones, siloxanes, polysiloxanes, substituted siloxanes and/or polysiloxanes.