I am 100% sure that it is the High Speed. The Low Speed runs constantly when the A/C is on. But if it is off then when the temp on the gauge creeps just past 1/2 (when high speed should engage), it doesn't. The low spped kicks in when it almost reaches the red, but WILL NOT overheat. It obviously only does this when the car is idling with the A/C OFF.

Paul Bobadilla 1998 Ford Contour SE Sport V6 2.5 Duratec