Heat transfer fluid with particular properties: suggestions?

Hello,  Can anyone suggest a candidate fluid for the following application?

Liquid at working temperature of about 0C, and between -10 and +50C. To be
used as heat transfer agent in a closed circuit system made of mild steel
amongst other materials. Must operate for years with no attention whatsoever
in an environment where a small amount of air ingress may occur, and must
not promote any significant corrosion in the system. Must be chemically
stable,  not exude vapour, gel, stick to surfaces or aggregate. High
conductivity / heat capacity not required.

Water is ideal from most aspects, except the requirement for zero corrosion
against mild steel.

TIA