I have missed most of this thread since, in my estimation, it has merited the
injudicious use of the delete key. As has all too much on list traffic
recently!

But a few points must be made here (and I am repeating info from individuals
laboring to infuse the discussion with facts):

1. All water, not pathologically purified and stored under nitrogen or argon,
will contain a variety of salts ranging from simple carbonic acid equilibria
through the simple halides to dissolved divalent cations and even a variety
of transition metals depending on the source and the storage media.

2. All antifreeze formulations take this into account and have a number of
chemicals in the primary solution so that pH and the dissolution chemistry of
aluminum, copper and iron are kept under control. The salts or hydrolyzed
ions that define hard water can complex or remove these reagents. The
reagents are often attacked by dissolved oxygen carries in the cooling
system.

3. The amount of control (translated into how long the additives protect the
cooling system from the effects of pH and aluminum oxidation) is a function
of how hard the starting water is and how much oxygen is injected into the
cooling system over time.

4. When the complexation agents are depleted (or evaporated to dryness in a
fixed air bubble in the water jacket of the head (example) a hard and
generally insoluble precipitate results. Film, scum, bad. This deposit
conducts heat poorly and often triggers cavitation. Bad.

5. Most dissolution of block, head or other multimetal components (water
pump) is triggered by pH changes or electrochemical redox reactions. Aluminum
is particularly vulnerable to attack with basic solutions (pH 10 and higher).
Copper is more readily attacked in acidic solutions, while iron goes either
way.

6. The singly most corrosive reagent in this system is ultraclean water.
Ultraclean water at elevated temperatures will dissolve Teflon, silicon
dioxide, silicon nitride, silicon carbide, hafnium nitride, etc., etc.
Ultraclean water is literally free of ions (sub-picomolar), carbon residues
(sub ppb) and dissolved gases such as CO2 and O2.

7. So for longevity, use water of moderate hardness (5 grains or less - ask
your water company) or filtered water as provided for steam iron applications
to mix the 50-50 solution with and Al compatible antifreeze. Bleed well
(remove air pockets). Vent to an expandable bladder cell (stops the
introduction of oxygen and CO2) with emergency pressure relief. For best
results, use a gasifier and deareate the cooling system while bleeding.

8. Switch to the Evans propylene glycol system and get rid of all this
nonsense (for a price).

RO systems good! Superstition bad! Down with political correctness! Chemistry
good, lawyers are politically correct.

Need sleep.

Frank Grunthaner