While the thermostat may open at 180, the cooling fan does not come on until about 220, so if there is not enough air flow thru the radiator, the temp can rise - I have seen this while sitting in a traffic jam - as soon as you start moving again temp will go right back to normal 185 - dealer says is normal
Saw this on my 2009 HHR. Got me in, Should I panic mode? Temp rose to 220 and as I was on with an Onstar Rep trying to get a diagnostic of my vehicle, it began to drop drastically. Went down to 185 before increasing again.