Q&A

water pump. the impeller is a common failure causing this condition.
take it to a shop to verify and get a bid.

Roy

The radiator might be clogged or the airflow restricted by debris. On some of these cars, not sure which years, the water pump can fail internally, the impeller comes loose of the shaft, and the engine will overheat.
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Have seen many of these water pumps fail due to impeller coming apart. The impeller on that stock water pump is actually plastic, and it will crack. If you personally have replaced the thermostat, then take it back out since you have an idea of what you are doing. If you look through the hole where the thermostat sits, you can actually see the back of the water pump impeller, check to see if it is cracked. You can also watch it, then have someone start the car, if the impeller is not turning but the steel shaft in the middle is, then you have found the culprit. BE VERY CAREFUL IF YOU ARE GOING TO TRY AND SEE THE IMPELLER MOVING WITH THE ENGINE RUNNING! I never advise customers to be under the hood of a car with the engine running. Good luck.

you need to chech the water pump some time the impeller in side split and it dose not cercle the coolent or your fan swith is bad the fan did not cick on on time that if your temp gage gose down when you drive on high speed or if you have leaking head gasket can do the same if you need help let me know www.mustangmogul.com