I have a Mustang, which is not the same as your Falcon, but similar. I have to say that 225° is not overheating - that's not even boiling temperature for a water-glycol mix under pressure.
I didn't see anywhere how full you are filling your radiator. My experience, and that of others, is to fill the radiator only so that the tops of the fins (you can see in the tank) are covered. Anything above that will be expelled. If you're filling the radiator all the way up to the top of the tank, it's going to puke until it has the correct amount of coolant in it.
Also, once you flush or drain the system, do you know that you need to let the engine run at idle for 20-30 minutes with the radiator cap off? This makes sure that all the air trapped inside is expelled and replaced with coolant. During and after this running time you should add coolant to bring the level up to the proper point.
I didn't see anywhere how full you are filling your radiator. My experience, and that of others, is to fill the radiator only so that the tops of the fins (you can see in the tank) are covered. Anything above that will be expelled. If you're filling the radiator all the way up to the top of the tank, it's going to puke until it has the correct amount of coolant in it.
Also, once you flush or drain the system, do you know that you need to let the engine run at idle for 20-30 minutes with the radiator cap off? This makes sure that all the air trapped inside is expelled and replaced with coolant. During and after this running time you should add coolant to bring the level up to the proper point.