Cooling system problem

[howie123]

I need help! I am nearing completion of a Model A speedster. Engine is 1928. I heard it run when I bought it 25 years ago. I cleaned it up, put in gaskets and such but no major engine work. The water pump was rebuilt using original style packing when the engine was put in the frame over 20 years ago. The radiator is new. I am running a 50-50 mix of water and anti-freeze. I have run the engine several times and taken a few short test drives. The engine starts easily and runs smoothly. I start with the spark at the top of the quadrant and move it down about 4 or 5 clicks after starting. The water pump has been leaking and I have been gradually tightening the packing nut. The leak seemed to be slowing until there was a loss of resistance in the nut. Now the nut turns quite freely in either direction but does not move in or out. The engine overheats quite quickly. If the radiator cap is off coolant will overflow the top. If the cap is on coolant will dump out the overflow tube. There is no sign of coolant in the oil or oil in the coolant. 1) Is it possible that the packing nut is screwed in past the threads or is it broken or stripped. 2) I am planning to install a coolant system filter to protect my new radiator. Any thoughts? 3) Is a thermostat a good idea and will it help the overheating? 4) What should be my first step at this point? Any help would be greatly appreciated. Thanks. Howie