I haven't been on the boards in awhile so I'm going to introduce myself just so you don't think I'm your typical Internet nutcase. ( I'm a special nutcase)
![Big Grin :D :D](/mustang-forums/styles/default/xenforo/smilies/biggrin.png)
I'm Eric I retired from my own auto repair shop about 4 years ago, I specialized in radiator, heating and AC, as well as doing general mechanics on the rest of the beast. At present I own a 65 ragtop,a 69 coupe, a 46 pickup and my daily driver is a 65 F-100 that I just put 4wd in.
Now back to your cooling dilemma, Just a couple of routine facts to get you started.
If you have an overheating problem it's because you are producing more BTU's than your cooling system can get rid of.
there are a number of things that can simulate overheating and get you to chase your tail for days.
Make sure the system is tight, any leaks can lower the pressure in the radiator and cause it to boil water.
Do a pressure test on the radiator cap, a cap that leaks pressure will allow the water to boil.
make sure your heater works, a lot of engines need the water to circulate threw the heater to properly circulate threw the engine block, if the heater is clogged it could cause water to boil.
BONUS; temp gauges can not be trusted, if the gauge goes up to a certain point and stop rising there is a very good chance you are not overheating. If you were making more BTU's than you could get rid of the gauge would keep climbing until it pegged itself at the top.
Check those little things and see how you make out.