Dist H2O - longish, sorry

[Jay Negrin <jmnegrin@domain.elided>]

Sorry if I am a bit late on this thread (Other issues have taken my time
for a bit) but this one has been around before, and I think I have said
the same thing then, as now:

Distilled (dist) water and de-ionized (DI) water are the same thing.
All of the minerals have been removed, either by (TA-DAH) distillation,
in one case, or by de-ionizing through an ion exchange column in the
other.  Both should have nothing in there but two part hydrogen, and one
part oxygen, by volume.

In both cases you end up with a fluid that can be quite corrosive, by
itself.  It does not "leach" minerals from the motor, but rather it
tries to dissolve whatever is containing it.  (Stainless steel of some
type, scupulously clean glass or certain types of plastic work well for
containing DI or dist water.  The pH of "pure" water is actually less
than neutral, maybe about 5.5 (pH 7.0 is neutral).

Tap water, which has *some* mineral content dissolved in it is, as Fred
dM points out, a conductor, while DI does not.  This refers to
electrical conductivity, which is of some concern regarding some types
of cathodic corrosion.  What I am not 100% sure on (I am a biologist
with some limited chemistry experiece) is whether the corrosion we are
most familiar with is due to cathode/anode type of electrical problems,
or are we talking about good old-fahsioned oxidation.  The latter is, in
ferrous materials, RUST, iron oxide.  It is also the white stuff that
forms on aluminium and its alloys.

Aluminum oxide forms the hydroxide in water solutions, at the proper pH,
and is truly obnoxious stuff.  It ends up being a sticky, gelatious goo
that can easily clog the tubes in your radiator and/or heater core.  As
Geo O would have said, double-plus-ungood.  Leads to overheating.  Also,
the aluminum oxide coating on the inside of the motor, while offering
some protection against corrosion, of the oxidative type, is a *thermal*
insulator.  The more you have, the more insulation you have.  Hence,
poorer heat transfet from metal to liquid.

Bottom line?  I, personally, do not think that it much matters if you
use tap or dist or DI water.  What is important, without ANY doubt, is
that you keep fresh coolant, in appropriate ratio, circulating with the
water.  The anti-corrosion additives are VERY important to the continued
long life of any motor, but especially to our aluminum marvels.  The
anti-corrosion additives that mfgs add to the coolant do get depleted
with time, so replacing the coolant regularly, at least every two years,
is important as well.

My two cents, well, maybe a couple more, because I have worked in the
water industry for a fair piece now.
If there are any chemists, metallurgists, or others equally qualified to
weigh in, please do.

Jay Negrin
ARO So Cal
76 Alfetta GT - come to think of it, should be about time to replenish
the coolant in that motor pretty soon.

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