If you read my first comment, I noted that distilled water is not “hungry” and is perfectly fine for radiators. It may help, and certainly can do no harm.
Ultrapure water is indeed “hungry” and will attack the metal of the radiator. But ultrapure water is probably not available outside of a laboratory or clean room manufacturing facility, and regular distilled water is not pure enough to be “hungry.”
This is my line of work. I have been the High Purity water field for 34 years. First off, pure water is very easily contaminated. Gasses from the air (mainly CO2 & ammonia) are very quickly absorbed from the air until pure water is reduced down to a low pH buffer point (~5.5 to 6). This is why distilled water is not as pure as deionized (demineralized or hungry) water. Deionized (DI) water has to be kept under a N2 blanket gas cap to remain pure or it will degrade within will a few minutes. DI water will also erode metals from pipes, etc. but only when there is a continuous fresh supply of DI water as the minerals will contaminate the water and reduce its purity. As far as using DI or distilled water in a radiator, as soon as you mix DI water with antifreeze it just becomes diluted antifreeze less the extra mineral content. Theoretically, you could use less antifreeze and still get the same strength solution because of the decreased mineral content of the mix water. We do this all of the time in chemical processing. Case in point: the very antifreeze you are talking about in this forum is made with a little corrosion inhibitor, a little glycol, some coloring, and a lot of DI water. Use distilled, reverse osmosis (RO), or DI water for your mixing. In the old days whe there was an embargo on coffee, we used to sell DI purifiers to office buildings to make their coffee. You can use ½ of the coffee grounds to get the same tasting coffee.
Hungry water seems just plain BOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOGUS
I would like to add a comment about what rwee2000 said about water conducting electricity. If the water is distilled to the point that it is absolutely with nothing dissolved in it at all, and it is 100% de-ionized, it will not conduct electricity. 100kw or so and above transmitting tubes use water cooling. Keep in mind though, that the water must be ABSOLUTELY pure or there will be BIG problems and if anything happens to the purity of the water, the transmitter must be shut down instantly or there will be an explosion!
The biggest solute in a cooling system is the ethylene glycol. When you mix water with antifreeze you not only alter the boiling and freezing point of the water, you reduce it’s ability to dissolve ions. Other ions in the antifreeze may include silicates, organic acids or phosphates, depending on the technology used. All of these bind rapidly to free metal sites on the surface of the cooling systems and act to reduce corrosion and prevent the solubilization of metal ions.
The ion content of tap water may or may not be compatible with these antifreeze technologies. Positively charged, dissolved, metal ions such as sodium or potassium are not a large problem, however calcium tends to form insoluble salts with both phosphate and organic acids. My other concern would be the presence of negatively charged ions like chloride, fluoride and nitrate which are very soluble and capable of acting as an electrolyte to speed galvanic corrosion. Tap water would be a poor choice for mixing with antifreeze due to contamination from these ions.
Distilled water obviously contains far fewer of these problematic ions. The argument that it could dissolve Aluminum, Iron or Copper ions is irrelevant as all potential ions in a system will come to an equilibrium based on solubility anyway. The best way to prevent these ions coming into solution in the first place is to reduce the amount of negative pairing ions in the coolant, which is why distilled water is recommended for mixing with antifreeze in your car’s cooling system.
Listening to your show this morning (8/13/16) a guest caller who happens to work in the basement of Car Talk Plaza and teaches at Harvard poo-pooed the Hungry Water Theory about distilled water damaging car radiators. I am sure he is correct, but write to say Hungry Water is an important concern in the field of dental laboratory technology. Until the recent advent of digital printing, still in its infancy, most dental appliances and devices such as crowns, inlays, bridgework, complete & partial dentures, etc., were fabricated on gypsum (calcium sulfate dihydrate) casts of teeth/jaws made from intraoral impressions. Such casts can dissolve significantly when soaked in distilled or even tap water, enough to compromise the accuracy of the cast and quality/fit of the final dental device fabricated. Soaking casts “Slurry Water” (saturated with calcium sulfate dihydrate) will greatly minimize damage, because the water is sated and not “hungry” for minerals found in casts. The most common use of slurry water is when mixing with dry gympus powder (anhydrous calcium sulfate) or similar products like concrete in order to speed-up the setting time. Hungry water is a real concern for dental lab technicians working with casts made from dental stone composed of gypsum.
Why can’t the the entire water cooling system just be at plate potential, like a bird sitting on a power line wire?, or use a fluid other than water, transformer oil comes to mind.