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Posted by D Sherman [72.47.153.24] on Sunday, February 12, 2012 at 12:46:36 :
In Reply to: Malarky. posted by Chriscase [76.212.213.55] on Sunday, February 12, 2012 at 08:25:52 :
Maybe in "high school chemistry" dissimilar metals cause corrosion, but not in college chemistry. For electrolytic corrosion to happen you have to have an electrically conductive solution, and generally one that's on the acidic side (salt, acid or dissolved gasses). Once water has been heated up to near boiling, all the dissolved gases come out of it. Until then, it can be corrosive. This is well-known to people who maintain large hot-water heating systems -- you don't want to change the water too often. Damp steel that's exposed to air rusts pretty fast, but steel that's totally immersed in non-salty, non-acidic, oxygen-free water lasts a long time. The rust-preventative in modern anti-freeze takes care of a reasonable amount of salt, acid, and oxygen in tap water. Distilled water is completely non-conductive and is therefore also completely non-corrosive. Distilled water is used as coolant in very high-power vacuum tubes where it has to insulate upwards of 20,000 volts, and it works fine. Hardness (alkalinity) in tap water is a bigger problem because it causes deposits that are hard to remove.
I suspect that the main reasons our water distribution tubes have rusted out is that either at one time there was a coolant leak and the old farmer, logger, or miner just kept refilling it weekly with fresh water and no anti-freeze, or the engine sat for years and the coolant level (maybe just plain water, or coolant that once had alcohol in it but the alcohol had all evaporated) dropped below the level of the distribution tube, exposing it to humid air for a long time. Neither of those things is going to happen in a restored truck, which means a new steel distribution tube will last at least until civilization runs out of oil, at which point all you can do is sit in the driver's seat and make vroom-vroom noises anyway.