Well, maxwedge, your vote is that plain water will do the job.
The -cooling job-.
Interesting.
Let me try to clarify it even more.
Plain water, as in PLAIN WATER. Tap, distilled, Poland Spring,
it don't matter. Think water without any coolant/antifreeze.
Again.....
Not concerned about whether it's a good or bad idea to run plain water as far as corrosion or possibly cavitation issues go.
IF the coolant system is filled with PLAIN WATER, will the system components be able to remove enough heat/BTUs to cool the engine, and keep the water below boiling.
Are modern Truck/Van radiators, water pumps, fans, etc. (mostly a radiator issue) sized large enough so that the higher boiling point of 50/50 mix is not needed? Or will the water temp. go high enough that it will boil....being PLAIN WATER?
Note:
The pressure in the system raises the boiling point of PLAIN WATER higher than 212F at atmospheric pressure. Does it raise it high enough so that boiling is not going to happen?
Another perspective:
Take a modern (2016) pickup truck with V8 engine.
Drain cooling system, and re-fill with plain water.
Drive truck around town at 30mph.
Will it overheat?
Drive truck up steep hills that require half throttle to climb.
Will it overheat?
Attach trailer, and load trailer to max towing capacity.
Drive truck and trailer up steepest hill in town with pedal
at near WOT and engine at max load.
Will it overheat?
Would it overheat with 50/50 coolant in it?
Hope this helps.