US Patent 7344655 Coolant, method of enclosing coolant, and cooling system

A coolant used for cooling down a stack of fuel cells includes: a solution mixture of water and a glycol as base material; and a rust-preventive additive that functions to keep an electric conductivity of the coolant at a low level and to maintain a hydrogen ion exponent of the coolant in a substantially neutral level. The rust-preventive agent includes at least one of an alkaline ethanolamine additive, such as triethanolamine, diethanolamine, or monoethanolamine, and an acidic additive selected among the group consisting of triazole compounds, phosphoric acid compounds, and organophosphoric acid compounds.