i have a 2003 impala 3.8L motor with a 180 degree thermostat in the car. normal operating temperature is usually 185-200 depending on the outside temperature and what kind of driving i am doing. but with the ac on and lately with the very hot summer weather while driving in stop and go traffic the temp gauge will hit about 215. does this behavior sound normal? i realize its only a 15 degree increase but it only seems to happen when its really hot out. the vehicle has a lot of miles on the motor and i'm just trying to gauge its cooling capability and make certain everything is working properly. the vehicle is very well cared for.