Coolant blows out and engine shows hot
 

2000 Expedition 5.4 L Eddie Bauer. 250,600 miles. Had overtemp light came on and temp gauge was over to hot.. Had driven less then 8 miles in single digit weather. Happened really fast toward the end in just a half mile. Thought I had blown a hose but no steam rose out even after I pulled over. After a tow home, pressurized the cooling system to 15 psi and it held. No coolant in the oil. Not sure where the coolant came from.that was on the drivers side of the engine compartment. Still have coolant in the reservoir but very low.. So probably not a blown head gasket but it sure has the same symptoms. Will check for bubbles in the reservoir and heavy vapor in the exhaust. Could be a bad thermostat but they usually fail open - not closed.. Anti freeze had not been checked in a while but ran it the day before in even colder weather. Plan to test for bubbles in the reservoir and excess exhaust vapor and let iit warm up to watch the thermostat. Any other ideas about what cold have happened here?
I did notice a loss of power just as the over temp light came on - possibly because of the shutting down of one cylinder to aide cooling as mentioned in this thread..

I would believe if the head gasket failed, coolant would overflow the bottle.I would wash down the engine to aid in determining the source of the leak. Just change the thermostat with an OEM unit and not mess around. It could be original and over 20 years old, they can indeed get stuck closed, don't assume anything. Test the concentration of the coolant, maybe it froze up in those frigid temperatures. I would also connect a scan tool to see the actual coolant temperature and not rely on the gauge.Do a sniff test on the exhaust gases and as a last resort, test compression.