2005 freestar. The temperature gage moving erraticaly. Sometimes to red, but 5 seconds later to less than half way back. And again and again. One ford dealer sells the the temp sensor, but there is non on the manifold. Other dealer said not all freestar has that temp sensor. Non of them can solve the temp gage problem. Is the engine overheating or not.

Sounds like your second geer piston seal is worn out and losing pressure,recommended good used or rebuild transmission.

Bad sending unit in fuel tank, or temp. gauge stepper motor bad

I'd also consider testing throttle position sensor with analog multimeter set on ohms. Remove and clean connection, connect to 2 of the pins at sensor until you see needle sweep as throttle increased,/decreased. Needle on meter should sweep across and back to coincide with throttle. Once you have that, increase throttle slowly and steady all way to floor and back slow and steady and watch needle on meter. If you see meter jump or drop quickly, test again and see if it happens same at same spot roughly. That would indicate a dead/bad spot in throttle position sensor, replace it. Needle should move smooth/steady up and down as long as pedal is doing same. Doesn't cost anything to test it.

most likely a engine or body ground could have been damaged or left of altogether by trans guy.

the condenser is in front of the radiator. you removed the thermostat and the car is still overheating? have the temperature checked with an infra red thermometer. looks like a gun. you just point the beam at the thermostat housing and it gives you the actual temperature. only takes a second. maybe the gage or the gage sending unit it bad.

This is nothing more than the tank sending unit that has failed. I would look into a junk yard and see about buying a complete unit(pump/sending unit assembly). It will be substantially less than new. Let me know if you need instructions on repair.

This happened to me last year.
Do not take it to the dealer or a transmission shop. Go to a reputable repair shop and have them replace the torque converter and trans. pump shaft. The shaft will come out with the converter. It should cost less than 1,000.00 to repair. My repair was 700.00. Request an aftermarket converter and pump shaft.

is the thermostat sticking from cold operation?
have you tried replacing it to see if it still happens?
if it does still happen, could be temperature sensor
the sensor might be cheaper and easier to replace 1st

The battery seems to be sending the wrong signals. get it replaced.

Change the Crank and Cam Position sensors

Very Common problem in those cars

I have changed 100's of them verry simple job

Jonathanri