Since the car does not overheat at slow speed, radiator is cooling the engine with pump speed and airflow through radiator. Since it is not cooling at higher rpm and higher speed, makes more heat to cool, air flow through radiator not enough, because of air going around nose of car instead of through radiator. that is why in my case the lower air dam helped funnel the lower air that was not being used to go through the radiator for more airflow.
