Abstract: 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.

Abstract: A back door hinge mounting structure comprising a pair of bolts connected with to each other at the central portion thereof and threaded at the opposed ends thereof, one end of the opposed ends connected to the roof panel with the other of the opposed ends to the fixed leaf of the back door hinge and a hinge cap for covering the mounting bolts which can be mounted and removed only when the back door is open, so that access to the mounting bolts with the back door closed is avoided.