Overheating and completely shutting down

Car was leaking coolant into cylinder head. That was replaced by a Ford dealership. However, they cannot figure out why it keeps saying that it is overheating and completely shutting down on them. When it did this they put the thermal gun to it and the engine is not really hot. They have replaced sensors, and check the radiator, but nothing is working. They have put a call into the main Ford Advisers. No word from them yet. Any ideas? Please help!