In a message dated 96-09-24 09:36:54 EDT, mathysj@kenyon.edu (Mathys) writes:
<< There is no particular reason why distilled water should be harmful to the
inside of the radiator. The problem with rust in the radiator is that it is
made out of iron (the chemically most stable form of iron is rust). >>
Distilled water by itself _can_ be harmfull to your radiator. Pure water is
a terrific solvent, has a high affinity for absorbing things, will gradually
eat out the iron water pipes in your house. When a brake master cylinder
gets large pitting spots down the bore, that's from water in the fluid eating
away at the iron, good cause to flush the fluid periodically. Similarly,
distilled water can attack the inside of your radiator to the point where it
finally leaks.
Water does however have a finite carrying capacity. If you load it up with
too much junk (minerals) the stuff will eventually percipitate out and coat
the surfaces with the minerals. Waterstone is calcium & lime, and rust on
the surface can be iron deposits from the water.
The trick is to get the right pH balance. On a 14 point scale with 7 being
neutral, a pH reading below 7 is acidic and above 7 is alkaline. Same as for
a hot tub, the ideal pH level is between 7.2 and 7.8. Below 7.2 you get
corrosion, above 7.8 you get deposition.
Note: Most water has entrained air, and the air in the water will still
cause rusting of the iron engine block, even when the pH level is correct.
The rust from the iron block gets picked up and circulated by the water
until it settles out in the lower reaches of the cooling jacket. In severe
cases the rust sediment can fill up to half the height of the water jacket or
more, restricting flow and causing overheating. Hot tanking and acid dipping
the block will not remove large amounts of rust sediment. It must be removed
mechanically. Remove the water pump, knock out all the core plugs, and dig
away with a coat hanger or some similar instrument to remove the sediment.
The good news is that antifreeze contains corrosion inhibitors and
anti-oxidants, and when mixed with water will prevent both corrosion and
rusting in the cooling system. Distilled water works OK, and ordinary tap
water usually works just as well. The additives in antifreeze do break down
over time, so you need to change the antifreeze about every two years or find
a way to replace the additives. The basic ingredient in antifreeze,
ethylene-glygol, will last literally forever, can be distilled out of the
used coolant and reused indefinitely.
Sometimes well water directly out of the ground has very high mineral content
in solution that can still percipitate out in your engine, even with the
antifreeze mix. This water will look murky and brown, and if left to set in
a glass on a table for an hour it will leave visible sediment in the bottom
of the glass. Do not use that water in your radiator.
Barney Gaylord -- 1958 MGA
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