overheating

["Cary Henry" <caryhenry@hotmail.com>]

I just reassemlbed my 76 today and started it for the first time since the 
restoration began.  I let it run for about 20 minutes so I could burp the 
cooling system.  Well, after about 20 minutes the car overheated.  The 
coolant was completely full.  I have never had it overheat before.  I 
rebuilt the water pump and replaced the thermostat when I had it apart.  Is 
it normal for these cars to overheat if they are just idling for a while, or 
do I have a problem?