Water, water everywhere. (A bit long)

[Stuart Thomson <stuart.thomson@domain.elided>]

Hi all,

Regarding the distilled water/deionised water in your cooling system.  This
has been hashed over many times, and the definitive answer depends on where
you live.

Firstly distilled water will conduct electricity Fred, there is CO2 dissolved
in it to form carbonic acid, which lowers the pH, and allows it to conduct
electricity (not well, but enough).  As also mentioned it lowers the pH which
starts to dissolve the Aluminium parts of the motor, Aluminium salts are also
highly acidic, which lowers the pH further, speeding up the process, it really
doesn't matter whether you have one of more than one metal, as the H+ ions in
solution will be reduced to H2, allowing Al to go to Al3+.  In short distilled
water is not better in terms of corrosion than tap water.  Once you add
antifreeze, things change.  Glycol is the main ingredient in antifreeze, it
has virtually no effect on corrosion at all, it's job is twofold, firstly to
raise the boiling point and lower the freezing point of the coolant, and
secondly to lubricate the water pump.  The green stuff is a redox indicator,
but there are other salts in there which inhibit the aluminium dissolution
process, and hopefully neutralise the pH.

Deionised water is exactly that, water stripped of it's metal and mineral
content and their counter ions.  It should be pH neutral and is probably what
is used to make up the ready to use coolant.  I see no problems with using
deionised water in conjunction with a good quality antifreeze/corrosion
inhibitor.  There can be problems using deionised water alone as it can
dissolve the other deposits in the motor, causing corrosion because there are
no inhibitors present, also it's not good for your water pump.

Tap water varies in quality so much it's hard to advise.  Here in Melbourne
and much of Australia it's fine to use as it is soft (little mineral
dissolved) and only slightly lower than neutral pH, so mixed with a good
quality antifreeze (antiboil downunder) with corrosion inhibitor concentrate
it's fine to use. In areas where the water is hard, you should use something
else, as the Calcium salt deposits (scale) will tend to block the cooling
system.

Fred mentioned that the insides of the motors that have used distilled water
since new have been clean.  This is not surprising as the people that go to
the trouble of putting distilled water in their coolant, probably use
antifreeze/corrosion inhibitor and flush the system regularly, which would
negate any of the bad effects of distilled water effectively.

In summary, unless you live in a hard water area, it doesn't matter what water
you use (tap, deionised or distilled) as long as you add the right additives,
and change it regularly.  The reduced cost of using tap water should make it
easier on the wallet so you can change it more frequently.

Cheers
Stuart Thomson

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