My temp gauge was stuck pegged after overheating, even with the engine OFF. I unplugged the temp gauge sensor, found the old sensor had shorted, a new sensor fixed that after the gauge "decided" to unstick from the hot position. Just unplug the black plug that is attached to the brass device right below the throttlebody, to the right of the waterpump in this image:
duratec If you unplug it, the gauge will stay cold until you replace and connect the new sensor.
