1988 Plymouth Horizon installed new thermostat, engine now

Two years ago, the bottom clamp failed and the engine coolant emptied out. Had it repaired with new thermostat. Let gas get too low in tank recently, had the fuel filter and system cleaned out. From then on found engine gauge redlines from cold start after 3-4 miles driving. Had thermostat again changed, but still does it. Each time it redlined, I shut the engine off and the top rad hose is cold. After 1-2 minutes, I restart it and the temperature gauge drops to normal range, where I can continue driving with no problem. The mechanic now thinks it may be the head gasket. I'm thinking it is an air pocket in the coolant system behind the thermostat. He did try bleeding off the ria from the rad, but didn't open the Allen bleed plug to drain the air off if that is the problem. Any ideas appreciated.