Confused about what kind of water to use in your cooling system (tap, distilled, reverse osmosis, holy)? The following is a post from the FerrariChat forum, by Jay Ross, a chemist at Applied Chemical Specialties: ...regarding reverse osmosis versus distilled water. By way of background, our group has over 40 years experience in industrial water treatment, and almost 20 years experience in engine coolant chemistry. Our industrial water treatment experience includes corrosion inhibition and scale control of high/low pressure boilers, as well as microbicides, inhibitors, and scale control for industrial chillers, heat exchangers, cooling towers, etc. We are active members of the ASTM D15 Engine Coolants Committee, and we are involved in the research, development, and manufacture of a variety of different types of engine coolant technologies. As Tazandjan correctly pointed out, distilled water is basically a purified condensate. What we have noted over the years is that condensate water can be a electrochemically aggressive to some metallurgy, under some conditions. For this reason and others, most industrial boilers utilize various forms of chemical treatment for condensate return lines. In our experience, we have noted that there are some aluminum alloys that exhibit particular sensitivity to distilled water. Additionally, we have noted that some distillation processes allow chloride ions to carryover. In either case, the result can (under some circumstances) result in fairly rapid oxidation of aluminum in modern automotive cooling systems. Youll know when you see it, as there is typically a white aluminum salt present as a byproduct of this type of oxidation. This can, and often does, cause leaks/failures in aluminum radiators. Chloride ions are extremely small, and can/will carryover through some water distillation processes. Their tiny size also allows them to easily penetrate aluminum alloy surfaces, which can result in an autocatalytic oxidation process that wont cease until the entire thickness of the alloy has been penetrated. For this reason, the ASTM D3306 Standard Specification for Engine Coolant for Automobile and Light-Duty Service specifically stipulates a maximum concentration of only 25 ppm chloride. On the other hand, reverse osmosis (RO) water is electrochemically balanced, and completely devoid of chloride ions. It is some of the purest water on earth, and represents the best and most reliable method of chloride ion removal. For these reasons and others, we do recommend its use as makeup for automotive engine coolant. Separately, the reason why distilled water can be more safely used as engine coolant when going with a 50/50 mix is that essentially you have half as much of it. In a 50/50 mix, it is of course half the concentration, as the other half is glycol from antifreeze. As such, the concentration of any contaminants that may be present in distilled water will effectively be diluted by half, and represent less of a risk. Additionally, we have noted that distilled water is not nearly as electrochemically aggressive to aluminum when compounded with glycol in a 50/50 mix. So this is why we state that RO water should be used as straight water coolant, but distilled water can be safely used if going with a 50/50 mix. While the merits of RO water have been known for a while, it has only been in recent years that it has become so easily available to the public in the form of bottled drinking water -- which can now be found at nearly any grocery store or supermarket. For this reason, recommendations to the consumer have been updated/changed in the last few years. I hope that this information is helpful. Thank you. -Jay Source: ferrarichat/forum/142410350-post65.html
Posted on: Sat, 25 Jan 2014 15:00:00 +0000
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