Before i installed the thermostat, it overcools on highways and overheats on traffic.

Now it is thermostat equiped it stays at 180F before open driving then stays between 180F & 200F on open driving. the problem starts on traffic. with the aircon on, it rises faster. with the aircon off, it doesnt rise that much. both situation with hood closed. i have this feeling that tells me an airflow problem.