Dave, etc.

The warnings that the other posters gave, are probably true, but there is at 
least one other thing to check; that's the valve for the coolant overflow. 
 The thing has two purposes.

First it holds the coolant pressure to (14lb/inXin?) while the engine runs. 
 The cooling system is normally pressurized by combustion gasses oozing past 
the head gaskets. They get trapped in the top of the expansion tank, and are 
vented by this valve when the pressure gets excessive.

Second, the valve must open when the cooling system pressure gets less than 
atmospheric.  This is to recover coolant from the overflow that may have 
spurted out along with the combustion gasses during the venting that 
normally occurs during running as above.  The pressure becomes negative as 
the engine cools and the coolant contracts and water vapor condenses.

Failure of this second function would cause your symptoms.  In other words, 
some coolant is normally carried out to the reservoir during normal running. 
 When the engine cools, instead of coolant being recovered through the 
valve, the negative pressure is satisfied by the hoses partially collapsing, 
etc..  The next run cycle dumps a little more coolant, and so on.

So, I would check the valve.

Mike

Michael A. Radtke  -  Z74               Voice: 602-862-4897
Bull                                      FAX:         4853
13430 N. Black Canyon Hwy.
Phoenix, AZ  85029                      Email: m.radtke@bull.com