Coolant Is A Misnomer...
The Mercedes-Benz product is correctly labeled "Antifreeze Anticorrosion Agent"...
The term "coolant" was applied to antifreeze by marketing people who wanted to increase sals during the summertime. They expected that using just the term "antifreeze" would make peple think that they didn't need to use it during warmer weather. Although these substances do raise the boiling point of water when added to it, they really do not provide any additional cooling ability.
The previous explanations of the thermal aspects are correct as far as my understanding, so you might try adding some antifreeze to make it a 60/40 mixture, or perhaps JimF. will pick up on this thread and share his knowledge again. As I recall, he runs a higher ratio mixture like you describe.
"We drive into the future using only our rearview mirror."
- Marshall McLuhan -
Northern California Wine Country...
"Turbos whistle, grapes wine..."