I have a 1966 Mustang with 289 engine with no AC. I recently replaced my water pump as it had a small leak. Ever since my car has been overheating. I then replaced the 180 F T stat. While replacing I noticed that the old thermostat was stuck open so I was happy to have replaced it. It still have over heating problems. I then raised the car on ramps and tried to burp the cooling system. I then took it for another drive. I drove about 20 km and It started to over heat again. I decide to take my car to Jiffy lube so that they could flush out my coolant and pressurize my cooling system. I thought maybe there was air in my system. That didn't work either. I took temperature readings with my laser temperature gun. The rad was hot and gurgling and coolant was coming out of the over flow hose. I don't have a coolant reservoir. Perhaps it was overfilled at Jiffy lube. The temperature readings were... Top hose 200 F, the bottom hose 175 F, Water pump housing 220 f, Thermostat housing 224, engine block close to thermostat sensor 234 F. I took off my upper rad hose to see if I didn't put the thermostat backwards by mistake. It was installed correctly so that isn't my problem unless it's defective. When I leave my car parked over night I do have a small leak. About 1 1/2" round. It's directly under the bottom rad hose. Unfortunately I can't see where it's coming from. Today I will clean up engine bay to remove all the coolant spills in the engine bay just to make sure. I'll also take a closer look for leaks. Any other suggestions?