I want to use a pure glycol because it is cheaper than anti-freeze

A word of caution: pure glycol contains no corrosion inhibitors.  Using this kind of product in aqueous solution may cause severe corrosion to your circuits.

Even if the pipes are made of stainless steel, if you have a different alloy somewhere in the system (eg copper in a heat exchanger), you will have galvanic coupling and we do not know in this case which allow will act as the shield to the other.