Methods for cooling a fuel cell include providing in a fuel cell coolant system an aqueous fuel cell coolant composition having an initial electrical conductivity of at most 50 .mu.S/cm. The fuel cell coolant compositions include an alkylene glycol and water solution, and an additive consisting of one or more five membered heterocyclic compounds (azole derivatives) having 2 or 3 heteroatoms selected from the group consisting of nitrogen and sulfur, which contain no or at most one sulfur atom and which may carry a fused aromatic or saturated six-membered ring, and an orthosilicate in an amount to provide a silicon content of from 2 to 2000 ppm by weight.