I have a 2008 Solstice GXP. I have a BAD over heating problem in the summer about 5 minutes into a drive when the temp inches up to 260 degrees momentarily, and then drops to norm) . It only does it from a cold start first thing in the morning IF I don't keep it under ~50MPH for the first few miles. Doesn't do this after being parked all day. Early spring or late fall the temp might go up to 220 degrees vs 260. Seems like a sticking thermostat but dealer wants $400+ to replace it on the turbo'd GXP (hard to get to it??).
I am the second owner and haven't removed the cap as mentioned. Does this sound like an air lock, a thermostat, or electrical problem?