I am an industrial chemist who worked on automotive and marine coolant additives (for both petrol and diesel engines) upto about 10 years ago, so some of these comments here may be valid to locomotive systems. Thermodynamics of a water/polyhydric (glycols, glycerine, sorbitol) and water/monohydric (alcohols) system will be different from that of plain water. The thermal capacity and viscosity of any given system will vary (widely) according to the chemical added to the water and its concentration. Therefore the heat exchanging rate will vary (dramtically) accordingly. Given any design of heat exchaging system (radiator etc) it will only work correctly if the right mix of coolant is used. The design coolant may be water.
I am unaware of the carbonisation effect described that freezes up piston/oil wiper rings, polyhydrics/monhydrics are as volatile and as combustable as diesel fuel oil, they are often added to fuel in small quantites to achieve a cleaner burn. If coolant leaks past into the cylinders I think the problem may be with the other anti-corrosive salts that are added to coolants such as Borax and Sodium Nitrite. These can be substitued for organic materials such as Benzotriazole and TriEthanolAmine OrthoPhosphate which again are combustable. All this is published material if you look hard enough.
Coolants are added not only for the depression of freezing point of the water system, but also for elevation of boiling point, very useful if you also pressurise the system. It allows the engine to operate at a much high temperature and therefore better thermal efficiency, hence creating a potential for high power outputs. Hope this helps. Harold Collier