Classic/Antique Car Repair: Packard radiator

Question
I have a '40 Packard Super 8 that has a tendency to lose coolant through the overflow tube after the car is driven any distance.  The car does not have an overflow tank.  After this occurs, the coolant level in radiator recedes below the filler neck.  Is it just seeking its own level, or should I continue to refill it to an inch below the radiator cap seat?

Answer
The most common causes are over filling, defective radiator cap and engine running hot. Remember that when you shut the engine off after running a while the temperature will spike and this could cause some boiling. The pressure cap is supposed to raise the boiling point of the coolant and prevent the spill over. Most of the time over filling while vent out of the overflow tube while you are running down the road. I would either replace the pressure cap or have it tested.