NEHA

3 degrees per 1 psi increase IIRC.

Probably 212F since most of the old stock cooling systems we run would probably immediately puke at around 20psig.


So, my original question still remains... From the standpoint of engine cooling system corrosion it better to use distilled or purified water in the radiator and why? In each case one COULD add rust inhibitor and lubricant additives (which I will do) but which water would require less of that additive to not screw with the cooling system? Again, my reading on this suggests to me there is no industry consensus as I have read use this but not that type water on both sides expressed with equal conviction. There must be a single science (not to say manufacturers dont regularly make up their own). Maybe neither is perfect in its own way (as I am beginning to suspect) and the correct choice depends on the additive package in a given "water wetter"?

This is the conclusion I have come to for selecting type of water (distilled, deionized, or softened) to use along with wetters in the cooling system...

Read the wetter tech sheet or instructions and follow them. Different wetters have different additive packages aimed at stabilizing or neutralizing a specific water type (or types) as none of the types of water are perfect or perfectly stable.

For instance Redline and Motul recommend using distilled water. Amsoil recommends softened water and cautions AGAINST using distilled unless in a 50/50 coolant mix (where the antifreeze is expected to stabilize the distilled water).