[pHaestus]

the anticorrosive properties of diols come from them having alcohol funtional groups which will do the following reaction in water:

R-OH -> R-O- + H+

For ethylene glycol the pH this happens is around 11-12 I think (making antifreeze a fairly basic additive). Now what happens when you have Ca2+ or Cu2+ or Al3+ in your system? It reacts with diols (meaning 2 alcohol groups per molecule) like this:

R-OH + Cu2+ -> R-OCu+ + H+
R-OCu+ + R-OH -> R-O-Cu-O-R + H+

See the Cu is chelated by the two groups of the diol making it unreactive with respect to reacting with aluminum in the system. You could easily write the same reaction for diol-aluminum interactions. Note that two protons are generated by this reaction; as the diol complexes the metal ions in solution it lowers solution pH too.

I assume if this fluidXP stuff is pH7 then it has a fairly high concentration of some buffer or other that keeps pH at neutral.