Jimm 1/5/2013Possible leak points include; hoses, the radiator, heater core, water pump, thermostat housing, head gasket, freeze plugs, automatic transmission oil cooler, cylinder head(s) and block.
Make a careful visual inspection of the entire cooling system, and then pressure test the cooling system and radiator cap - with the engine and system cold. A pressure test will reveal the leaks. A good system should hold 12 to 15 psi for 15 minutes or more with no loss in pressure.
It is important to pressure test the radiator cap, too, because a weak cap (or one with too low a pressure rating) may be the leak source.