Temperature

I've Only owned My 2004 Chevy Cavalier 5speed 2dr 2.2L SFi for over 3weeks now and I notice today that when I had the inside Fan On and it was hot earlier 90 degrees, the Temperature went from the normal 190 degree just a little below the half of the line and went up a little bit to maybe 205-210 degrees a little bit above the half of the line and that was Only when I was just parked at a parking lot trying to make a phone call, when I left the spot the Temperature needle went back down to normal just below the middle half line 190 degrees. Is this normal for this car or does it mean I need to change the Coolant? and also any idea of where the Thermostat is located for this car? Thank you very much in advanced.