Heat transfer fluids are used in the presence of metals and/or Lewis acids of mixtures. The heat transfer fluids comprise (A) hydrofluoroethers and/or hydrofluoropolyethers, liquid under the environmental conditions (25° C., 1 atm); and (B) a compound having a fluoropolyether structure having end groups selected from the pyridine, amine, and aryl classes. The heat transfer fluids have a number average molecular weight of between 400 and 10,000.