You dasn't ever want to run straight H2O in your cooling system.

I just went out to the shop and checked a container label for engine coolant (Wal-Mart variety). Sez boiling point for 50/50 mixture with H2O is 265 deg.F.

Put a 16 psi cap on that and it goes up some more.

Yes; the boiling point goes up; but the ‘specific heat’ – the ability of the fluid to absorb heat - goes down by roughly the same percentage; thus for the same flow rate, you are removing about 25% less heat.  It is further aggravated because of higher viscosity, it also reduces flow rate.  Lowering the specific heat (a.k.a., heat capacity) and the flow rate increases the temp change through the engine and rad, increases thermal stress and may reduce radiator effectiveness.

So there is a tradeoff.  But you’re right, don’t run straight water.  The ethylene-glycol coolant comes with corrosion inhibitors; so if you don’t dilute with e-g, by all means add corrosion inhibitors.

The argument for using e-g/water or not is probably case dependant, it depends on what is the limiting factor in your cooling system.  But I’d say that if you are having cooling difficulties with e-g/water coolant, try straight water with inhibitors.  It may make things better.

Al