coolant, water and mythology - longish

[JMNegrin@domain.elided]

Several days ago, one of our friends on the Digest posted something to the 
effect that hard water dissolves heater valves.  In response to that, and 
respond I must, I will state that hard water should not dissolve parts.  The 
softer the water, and/or the lower the mineral content, the more "agressive" 
that water may be.  Harder water may leave deposits, which in turn could 
screw up valves seats and seals in a water system, but I don't think 
corrosion is a direct result of hardness or mineralization.

There are other elements of water chemistry (alkalinity, Langlier index, and 
more) that come into play here, but the biggie is pH.  The lower the pH, the 
more water will act like an acid.  Pure, distilled or de-ionized water has a 
pH of about 5.5.  Neutral is pH 7.0.  With no dissolved mineral content, and 
a low pH, pure distilled water is "aggressive"; that is it wants to dissolve 
anything it can, including your metal motor parts.

If there is a leaky head gasket, the carbon dioxide and other combustion 
gases can dissolve in the water and drop the pH a bunch.  This acidified 
water/coolant could be an active corrosive agent, but it is not the result of 
minerals dissolved in the water, but exhaust gases.

Starting with distilled, de-ionized or demineralized water is just that a 
start.  If there is no corrosion inhibitor(s), I would suspect a bad end to a 
cooling system, especially in an all alloy motor (such as our Alfas).  A 
proper coolant should have anti-corrosion properties as well as the glycol of 
your choice to raise the boiling point as well as lower the freezing point.  
It will do both, so referring to the coolant as 'anti-freeze' is a bit of a 
mis-nomer.

Jay Negrin
ARO So Cal
Water Quality Biologist (with a minor in Chem)

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