Hope others don't end up this way.
Ran like a beauty for the first six months I've driven her as a DD. Bought used with 50k miles and already at 70k. Had similar symptoms with a two spats of 'higher' temps at 220 during recent weekend trip of 300 miles. Went away pretty quick on the road.
Next morning, drove to work fifty miles one way and started overheating one mile from work. Babied it into my parking lot with the high temp warning light just turning on. I always have my display at oil temp and really familiar with what is normal (190f-200f).
Symptoms: Escalating temp at 240+, No heat from interior heater, hot upper radiator hose, cold lower radiator hose, no leaks, expansion tank level slightly higher than normal/hot, normal dark/black oil, no exhaust smoke or liquid.
Went through the wonderful information on this and other threads and did all of the air purge procedures many times after work. Same results, so next morning I changed out the thermostat in the parking lot and re-did all of the purging procedures. Still did not work. Found that the expansion tank level was rising dramatically with coolant/system pressure increased as it was getting hot, post-purged, with all the other symptoms still active. Blown head gasket is my call.
Towed to local GM dealer in small town after confirming my service contract company would work with them. The service guy seemed in a panic describing that they think the motor 'blew up'. Seems they aren't used to motor repair as they have to have an 'inspector' come in to make an assessment of what to do. Hope they are better at oil changes?!?!
Will post progress.