I've seen a number of suggestions in this and the 240 BB regarding flushing and refilling cooling systems and many of these suggest using distilled water along with the coolant. A while ago on the MGB board, (yes, I balance the pragmatic good sense of owning a Volvo, with the lunacy of a British sports car...) a Chemical Engineer cautioned against this and recommended softened water instead. He worked in the process industry, and had seen major corrosion problems resulting from distilled water use in situations where it can come in contact with CO2 and/or other gasses. The reason is, it has no "buffering" capability, and will quickly turn acidic when those gasses dissolve in it. IE: it becomes an electrolyte with serious corrosive capability.

Softened water contains compounds which will absorb/neutralize (buffer) most of such acidic reactions, and continue to be relatively harmless to metals. Perhaps the blending of "antifreeze" with the water makes the whole point moot?

Anyone out there with a chemistry background who can comment? Personally, I've used soft water for many years in my cars' cooling systems and seen no noticeable corrosion. The '83 244 is still on its original radiator and heater core and both function as new.
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Bob (81-244GL B21F, 83-244DL B23F, 94-940Sedan B230F)

Is he really a BS ChE? Does he run just water? wow

Steve and others got it right. This whole pure water thing is moving into the urban legends arena.

Mix good antifreeze coolant with the purest water in the world or if your area has low disolved solids use tap water. Change it every few years. End of subject.

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http://www.fidalgo.net/~brook4/oilslubesfilters.html

1)Yes, I believe so.
2)No.
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Bob (81-244GL B21F, 83-244DL B23F, 94-940Sedan B230F)

Well, I dunno where I got the idea for using steam distilled water as the antifreeze dilutant. When I started using it, back in 1979, I had reason to mention this use to a client who owned a radiator repair shop. His answer was "Keep that quiet, you'll put me out of business."

Ever since then that's what I've used. 50/50 green Prestone and steam distilled water. Never a problem that I could attribute to this mixture. I do have softened water in the house, and there is never a salty taste to it even though it uses a brine ion exchange system. Runs 2x a week, 3# NaCl each time.

Our water is otherwise about 10 grains hardness and over-average acidic. No hardness in the house, but what happens to the acid I don't know. It all comes from 180 feet below the side yard.

Maybe there is an automotive cooling guru around who will give us the deciding opinion.

Regards,

Bob

:>)

Great question. Many years ago a Ham Radio club I belonged to got a tour of a local plant that manufactured integrated circuits. We were shown the plant that produced "10 meg" water. That is, ultra pure, distilled, deionized water used to wash the chemicals off the finished wafers. It was highly toxic (we were told) and the pvc pipes used to distribute it needed to be replaced several times a year. The water needed some sort of buffer in solution to make it stable. In the case of the cooling system, anti-freeze provides this stabilization. Besides, distilled water you buy at the store is nowhere near "10 meg".

Skip
'93 850GLT
'83 242T Flathood
'89 765T

Well not so fast Steve, there is an element of truth to the distilled water as solvent angle. Yes, I was told distilled is a no no in metal systems. This by way of service people who maintain very expensive stainless autoclaves. The problem is not ions and corrosion but rather the solubilization of metal by water containing no ions. I am not sure a car would be affected too much by this solubilization effect, since the water is not flowing through but would come to equilibrium with the dissolved metal in a closed system pretty quickly, but these guys also recommend soft water emphatically. I no longer use distilled water in my cars. You simply can't dismiss the recommendation by competent people in the field though and in principle, when large amounts of water are handled, metal dissolution by distilled water is a problem. I just do not think in an auto cooling system (2 gallons) that you will dissolve too much of the head or block.

Bob, don't forget that you are adding the water to a chemistry package in the coolant, filled with a variety of tailored ions specifically for corrosion control. This package limits the oxidation of metals and the exchange of ions into the solution. But adding "softened" water (if it is made in an ion exchange process) defeats the purpose of the corrosion package in the coolant.
If one were to use distilled water only in a cooling system, I could buy the argument that the lack of ions might increase solubility of various components and the rate of oxidation of metal. Likewise, your friends in the autoclave business (operating machines using pure water) are probably justified in recommending ionized water.

Makers of antifreezes recommend distilled/deionized water. Knowing that people won't use it, they add certain additives to deal with hard water. But nobody I know recommends using soft water.

See this reference: http://www.nichols.nu/tip514.htm

His reasoning is completely misplaced and the conclusion drawn is absolutely wrong. "Softened" water has its "hard" calcium, sulfur and iron ions replaced with, generally, sodium; sodium is just about the worst thing you can put into your cooling system. Guaranteed, instantaneous corrosion. Some softening systems use a deionizing membrane to remove ions; only in this case can the resulting "soft" water be used in antifreeze and only if enough ions are removed to constitute deionized water.

Distilled or deionized water by definition has no ions. The coolant contains adequate buffers to alter the pH of the mixture to levels sufficient to prevent corrosion. If CO2 is entering the mixture, then it is due to a leaking head gasket; the least of your problems is then the pH of the coolant mixture.

Your friend is referring to other processes entirely and obviously does not understand coolant chemistry. ALL major coolant manufacturers either use distilled/deionized water in their pre-mixed products or recommend it for use with their antifreeze products.