All the articles I have read say a shroud is a must! These cars were always undercooled....consider a larger radiator.

 

Overheating is common. May be true, but Bu77sh1#. I just changed my Cougar to a 3 row. New thermostat. And added
an overflow. After all that, we think the issue was the fan was buried in the shroud. IT MUST BE halfway extended
out of the shroud. This is a must. I probably could have just changed the adapter on the fan and fixed mine. That's ok,
it needed the other stuff anyway. It runs fine now. Idle, no problem. A/C, no problem

 

Hi! ok_ee... I have a 66 Mustang with similar overheating problem. I do try some adds that you don't (like an aluminum radiator, electric fan, a more eficient water pump, etc.) and can't eliminate the problem. The engine was totally overhaul again, re-cheking all measures: pistons, rings, cam, cylinders, etc. I don't know were go from here. Someone tell me that changing the WP pulley by one smaller, could help. Another opinion was adding a fan shroud too, but I'm not so sure with this. I'm not giving up yet, and going to tell about my findings.

 

I'm having a similar problem with my 1965 289, the radiator boils over so bad I'm afraid the engine will seize up. Checked for cracks, replaced all intakes and head gaskets, new 4-row radiator, 6-blade fan. I've had several mechanics look it over and can't find the reason, I'm at a lost as to what to try next. Any more suggestions would be appreciated. Has anyone actually tried a hi performance water pump?

 

You want your trans cooler AFTER the radiator cooler. A cool auto is a happy, long lasting companion (mine typically run 150-180 with synthetic ATF in the summer).

As for the simple things: thermostat installed correctly (try running with just a restrictor and no t-stat. No stat+no restrictor=bad...one or the other)? How's the radiator cap pressure? How hot is your engine really? You could be running the coolant to quickly through the system as well (not likely here, because it is stock, but it is possible).