temp gauge way too high

[eclipse93b]

i was driving home last night and [about 5 miles from the gym] and i saw that i needed gas, i stopped got some, got close to my house and my temp gauge got about 3/4 of the way up, usually its at 1/2. i wasnt boosting at all and the temp inside the car got really hot, then i let it idle for a min, and the temp went back down?? i decided to check it out a little and so i took it slowly to a back road and gave it some boost [16 lbs] and the temp gauge went back up. i brought it back home and the gauge was normal then. and i popped the hood and didnt see much. [it was 1030pm in minnesota in january at about 10 degrees out.] i checked my coolant this morning and it is pretty dirty. i just bought the car and dont know when it was changed last. also there is alittle dried up coolant around my radiator [by the tstat] pipes. I also think that i have a air bubble in the coolant because i have poor heat at idle. Can anybody else help my out with an opinion on what it is??? im going to do a coolant flush today when i get home to see if that helps. on a side note the car was perfect this morning going to work and i boosted some just to see if it would act up again but it didnt.
sorry for the long post, any help would be appreciated.

kyle-

 

[x camaro owner]

bleed the cooling system after flushing, might take a couple of tries, check bottom of spark plugs for some green, to see if it is head gasket time. replace the thermostat for the hell of it to, and radiatior cap, simple cheap things that can ruin your day