A polymer electrolyte membrane (PEM) fuel cell power plant is cooled evaporatively with a water coolant system which does not permit liquid water to exit or flow through the coolant system. The coolant system utilizes a hydrophobic porous member (28) for venting gases such as fuel and/or air from a coolant water flow field in the system. Coolant water (36) is prevented from continuosly contacting the porous member during operation of the power plant thus preventing blockage of the porous member by coolant water or contaminants disposed in the coolant water.