NOVELTY - A fuel cell power plant comprises a stack (37) of fuel cells, each fuel cell having coolant passageways connected between a coolant inlet (66) and a coolant outlet (68); where a gas (65), which assures a velocity of fluid in the coolant passageways greater than zero, is communicated between coolant inlet and/or coolant outlet. The coolant outlet includes a gas/liquid separator having a gas outlet (90). The flow of gas is created by gas pressure from a source of pressurized gas, an oxidant reactant air pump, a source of hydrogen-containing fuel, or fuel outlet or outflow of a condenser.    USE - As a fuel cell power plant useful for generating electricity in vehicles.    ADVANTAGE - The use of gas for inducing flow within the coolant channels eliminates the need for a bubble-clearing liquid pump and reduces liquid inventory and other plumbing, thus making the fuel cell power plant more robust and more freeze tolerant, and preventing the aggregation of gas within the passageways which could impede or block the flow of liquid. The biphase flow from the condenser renders the coolant return flow more freeze tolerant. The gas applied to fuel cell coolant passageways assures coolant flow in small fuel cell coolant or water management passageways; mitigates bubble blockage in low-flow fuel cell coolant or water management passageways; assists gas bubbles to flow through coolant or water management passageways in proton exchange membrane (PEM) fuel cells; improves venting of gas in PEM fuel cell coolant or water management passageways; reduces excessive ingestion of gas into fuel cell coolant or water management passageways; increases gas flow toward a vent in PEM fuel cells; improves hydration in PEM fuel cells; improved evaporative cooling in PEM fuel cells; and reduces the number of components in the fuel cell power plant which have rotating parts.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is included for operating a fuel cell power plant involving communicating to a coolant inlet and/or coolant outlet, a gas which assures a velocity of fluid in coolant passageways greater than zero.    DESCRIPTION OF DRAWING(S) - The figure shows a simplified block diagram of an evaporatively cooled fuel cell system.    stack of fuel cells (37)    gas (65)    coolant inlet (66)    coolant outlet (68)    gas outlet. (90)