My daughter has a 74 Mustang II with a 2.8 V6, the bearing in the water pump took a poop...so I installed a new unit and thermostat....I installed antifreeze/water mix and started it with the cap off waiting for the thermostat to open up to top off the radiator....it never happened, the thermostat on this car is next to the lower radator hose not the top....so when the car warmed up the top hose got hot lower hose stayed cold...thinking bad thermo, I installed a new one...same thing, car does get hot but doesn't over heat....I noticed the thermo was a different type than the one that was in the car before...before it had the conventional type but the one the book specified had a extention with a round washer type deal to plug off the heater hose till warm up? Could this be it? Or....I've heard of bleeding the system, would this cause this problem....P.S. it looks like the radiator is new so I don't believe it could be clooged...thanks for the help