Temperature Gauge/Warning Light

I have a Ford F-150 with a 4.2 L V6. Lately during routine driving the temperature gauge often rises rapidly into the red zone and the warning light comes on. The engine is not overheated. If one turns the engine off and restarts it, the warning light is off and the temperature gauge is in the normal zone. Unfortunately, this happy situation only lasts for 2 to 10 miles.

My Ford dealer has tried and failed to solve this problem three times in the last four weeks. Help.

I would first check to see if the sensor is causing this problem. I would measure the resistance of the sensor when it is at normal operating temperature and showing normal on the gauge. Then when it is indicating hot. If there is a different resistance then you need to see if it is due to the sensor or if the temperature really has changed.

Usually, there are multiple sensors involved. There is the water temperature sensor that normally controls the gauge, and there are sometimes also cylinder head temperature sensors. If one of those goes too high, the computer will force the gauge to max reading suddenly. This sounds like what is happening here. If you have air bubbles in your cooling system, it might be that the sensors are correct, and parts of the engine might be getting too hot, for brief periods.

Your air bubble suggestion seems to pretty well explain what I see happening.
Can I get rid of the bubbles by running the engine with the radiator cap off or is there a more complicated solution?

I don’t know. You need to find the correct procedure for your engine. I know that in my case there are some bleed screws on the engine that have to be opened. (3.9L V8)

Was the cooling system opened recently, to replace a thermostat, hose, etc? That’s usually when air can be introduced, unless a gasket is leaking or something else.

Elevating the front-end of the vehicle usually helps with burping out the air and adding coolant in its place.