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Old 05-21-2020, 10:48 AM   #6
MikeK
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Join Date: May 2010
Location: Windy City
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Default Re: Distilled Water?

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Getting back to the OP's original Q, in many municipalities the tap water contains additives to prevent the water from attacking the iron water system street feed pipes and rusting them through.

The anti-rust treated municipal water works by causing calcium salts to coat and encrust the iron surface, blocking chemical interaction of the iron with the water.

Unfortunately (for iron engine blocks) running tap water in an iron engine block causes that tap water lime to deposit both in the radiator and over the block surface, reducing thermal transfer and eventually creating cooling issues.

Running distilled water, which is very ion-deficient, causes stripping of those deposits and a return to the iron rust problem. That is why you went from whitish with tap water to red with distilled!!

A lot of people say it is a crazy waste of $$ to buy 50/50 pre-mix antifreeze, but that stuff has none of the problems of either calcium rich tap water or ion deficient distilled.

A name-brand 50/50 pre-mix contains water that has been reverse-osmosis processed, is free of calcium, is pH balanced, and has the correct ion additive enrichment to work with the glycol without problems.
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