At 09:51 PM 4/19/2004 -0400, you wrote:

        Water will often freeze in the radiator if you do not have anti-freeze, even if the engine is warm. The freeze will start in a low flow (water) region and will then spread as the flow is further blocked, perhaps bursting radiator tubes as it progresses.
        
         I certainly can't prove this isn't true, but someone would sure have to prove that it is, before I could believe it.  I just don't see how rapidly moving, hot water is going to freeze. 

        "Rapidly moving" is the key phrase. The problem is that often the water does not move rapidly everywhere at all times. For example, some corner of the radiator (like the drain cock) may have a lot of air cooling, but very little water movement.