If you have the old Ford expansion tank, the one that mounts on the thermostat housing, there should be no holes in it that weren't put there by Ford. That is, a fill spigot with overflow, the outlet at the thermostat and the inlet from the top radiator hose.
That tank has a horrizontal baffel with a hole in it just below the cap opening. That hole, in the baffel, is the fill line for this tank.
Obviously you want all the air out of the rest of the system and a good mixture of coolant in the system.
My experience in getting the air out is to fill and burp as much as possible cold, then drive it, let it cool and check the level. This may have to be done several times.
The thermostats I have seen have enough bypass that an additional hole does not help in bleeding air out of the block.
A 50/50 mixture of
antifreeze works best in that it gives optimum freeze protection as well as the best heat capacity increase over plain water.
The system should have an overflow line coming off the fill cap spigot on the expansion tank. The "radiator cap" there should be good for around 16 psi. Check the specs of the donor car and /or an informed engine builder / tuner to determine if that is enough for a modified engine.
If you have a cap on the radiator as well, it should have a pressure rating that is equal to, or slightly higher than, the one on the expansion tank. There will probably be an over flow tube on this spigot as well.
To the best of my knowledge, these overflow tubes won't work with a recovery system. The stock radiator cap on the old Fords was for over pressure relief only. There is no way the system can draw fluid back through these caps since thy are designed to hold everything in up to their "pop" pressure, at which point the fluid goes out the end of the over flow tube to the ground.
The tank itself is designed to contain the expanded water from the hot block with no loss of fluid, hense the name "expansion tank".
A severe over heat situation will cause the pressure cap to let fluid escape to accomidate the additional volume of fluid expansion due to the higher than normal temperature in the engine.
The space above the hole in the baffel is calculated, by the Ford designers, to hold the increase in volume of the normally hot water, don't put any aditional fluid there or it will pe pushed out as soon and the block starts to heat up.
If you are loosing water at normal engine operating temperatures the pressure cap may be bad, or another system leak may be present.
If the water temperature is always extremely hot after slow speed driving, the radiator may not be big enough, the water flow may not be sufficient (due to the pump or clogged radiator) the air flow may not be sufficient to extract the heat from the radiator of a combination of all these things.
A good friend found that the three core radiator (with large oval cores) worked better than the four core he took out.
I have seen some fan installations that inhibit good air flow as well.
Look at the size of the fan the old Fords had on the stock installation, the size of the radiator and the volume of air that was drawn through when the, engine driven, fan clutch engaged.
If you are not moving that much air through that much water you will probably have a heat problem.
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