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On 14 Jun 2006 at 1:29, John Jaranson wrote: > My understanding and experience is that when a thermostat fails due to > a breech of the bellows, it expands to its full height. This indicates > to me that the free state of the bellows is expanded...so what ever is > in there must change state (solid to liquid or more likely liquid to > gas) at 165F as JIm stated.....but it must be put in and sealed at the > hot state (expanded) and then as things cool down and it condenses (and > shrinks), the vacuum created contracts the bellows. > > I think this would make it harder to do a home repair on a damaged > bellows. I agree with your theory of operation, but I don't think it would be TOO hard to do a repair. I'd try putting a very small amount (~1/2 tsp) of the liquid in the body, with the bottom sealed up, then, with the whole thing on a hot plate so that the liquid was very gently boiling and filling the body with vapor, I'd try to seal the top solder joint. I suspect that these were originally made by just heating them in an oven that was filled with the appropriate vapor. They probably just used solder preforms which flowed once the right temp was reached. Oven soldering like this can be very easy if the vapor is flammable, because that means that it will scavenge oxides off the surface of the copper/brass leaving it very clean and solderable. This is a standard technique for brazing, but I've not heard of it for soldering. The oxide scavenging might not work as well at the lower soldering temp, but if the parts started out clean it should still be enough. The main thing would be to keep oxygen out of the furnace atmosphere. Most of the bad ones that I've seen seemed to have suffered from a broken solder seal. If the bellows actually cracked, I don't think you'd have any real chance of making a lasting repair. Since Russ says they smell like alcohol, I just looked some up. Methanol boils at ~65C; ethanol boils at ~75C. Sound familiar? ;-) Bob Hudson claims to have seen some which failed in the collapsed position. That actually seems like they would be harder to make and virtually impossible to inspect for duds after they come out of the soldering furnace. I don't know why anyone would try to make them that way, but I have no reason to doubt Bob. -- Jim Adney jadney@vwtype3.org Madison, WI 53711-3054 USA ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ List info at http://www.vwtype3.org/list | mailto:gregm@vwtype3.org ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~