1996 Ford Thunderbird mileage: 56,000. The problem I had was the temperature gauge would fluctuate going very fast to hot, stay for a minute or so then back to cold very fast. My mechanic changed thermostat. It worked for about a day, I took it back to Mechanic three times with the same problem. Each time he changed the thermostat. This happened about three times. Finally, he installed thermostat for a turbo charged 3.8 engine. The car now takes a long time to heat up. Do you have any knowledge of what is going on with this car? My mechanic is at a loss and he does not know what else to do. He even consulted with the Ford people. If you have any explanation on this, it would be very greatly appreciated.
Check for air in the cooling systems and check the radiator cap to see that it is working properly (pulls coolant from overflow tank when engine cools). Also, check the water pump impellor as we have found the impellors sometimes fail or corrode away resulting in insufficient coolant flow.