I believe that glycol is added as both an antifreeze and to marginally raise the boiling point of the coolant. Dieseldiehard is right about the less effective heat transfer. Ask any racing mechanic and they'll tell you the preferred coolant is water with a lubricant/anticorrosion additive.

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LRG
1987 300D Turbo 175K
2006 Toyota Prius, efficent but no soul
1985 300 TDT(130K miles of trouble free motoring)now sold