Erratic temp reading

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bethlhem
97’ 4.6L ford expedition erratic temperature reading.

Been having problem with overheating and loss of coolant. Occasionally when this overheated, the check engine light would come on (code P1299) and the truck would go into limp mode.

Steps take so far to correct: Changed the upper and lower air intake manifold gasket, new thermostat and gasket, new fan clutch, new water pump, new radiator, new coolant reservoir and cap.

Burped the coolant system several times. After Burping, let sit for 2 hours. After driving for 2 miles temp jumped to 244, dropped back to 189 after 3 -4 min. (Reading live data on code reader)

After sitting for 8 hours, drove 5.2 miles and temp jumped to 243 and back to 189 three times.

Im reading the live data on the code reader and the temp gauge on the instrument panel indicates the same (with a slight delay)

Note that Ive always had a problem with heat in the cabin. Ive flushed the heater core with vinegar and have full flow through but I suspect the smaller capillaries may be blocked. The blend door opens and closes but I do not get heat. I mention this as a consideration that it might be related to the engine overheating in some way.

Im looking for next steps. I was considering changing the temperature sensor(s). Can you tell me which sensor sends data to the PCM and to the dash Gauge? Are they the same sensor? There is a air temp sensor and a water temp sensor on top of the manifold. Help plz.
 

podsquad

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Head gasket...get a thermostat with a check ball. It worked for me....it releases the gas building up...that pressurizers the system.
 

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