Date: Sat, 18 Dec 2004 08:49:36 -0500
From: Fred W <>
Subject: Re: steam at radiator (c900)

Al wrote: > "John B" <> wrote in message > > >>The exhaust leak turned out to be easy to find, as it was a giant crack in >>the >>intermediate pipe (between the catalytic converter and the mid muffler), >>just >>aft of the collar where it bolts to the catalytic converter. I undertook >>to >>replace it myself, which was successful though a pain in the ass: the >>bolts >>holding the old collar to the catalytic converter were rusted beyond hope >>and >>had to be sawed off; and the intermediate pipe was separated from the mid >>muffler only after extensive heating with a blowtorch and much swearing. >> >>And regarding the steam at the radiator, I dumped some Prestone brand >>radiator >>leak stopper into the system-- only time will tell whether that helps >>anything. >> >> >>John > > > I read the threads on the steam thing recently and didn't have time to > reply. > > For what its worth, on my C900 I came to the conclusion that it was > condensation on the engine block, built up overnight. Because:- > 1/ I only noticed this in cold weather, when dew was likely. > > 2/ There was sufficient steam to indicate a leak, but no leak could be found > > 3/ The water level simply refused to drop a millimetre in a year of > motoring. > > I don't like water or oil additives, if you really have a leak, you need to > fix the leak not fill the system with crud! (does anyone else remember the > Mike Harding sketch and the eggs in the radiator?!) > > Cheers > > Al > > My take on a likely source of this mysterious steam: (and I do remember this as a regular "feature" on my 1990 900) When the engine cools and the fluid in the closed cooling system contracts it draws coolant from the overflow tank which creates a small vacuum in the tank. If I'm not mistaken, there is a poppet valve in the pressure cap that allows this vacuum to be relieved by drawing in outside air. When you next run the car and the heated coolant expands it can eventually exceed the pressure rating on the cap (12-15 psi?) and release some of the air from the reservoir. This could be the source of the steam. If this is the source, it should be easy enough to see if one were to watch it through an entire warm up cycle. But then again, I suppose this would fall into the "watched pot" category. It probably would not happen just because you were expecting it to... -Fred W

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