I have a 1998 ford escort lx SOHC. my cooling fan is not kicking on when i am idling and my car starts to overheat. It cools down if i am on the highway or constantly moving, but it cools down below operating temperature, probably down to around 1/3 of the way up the gauge instead of around the normal 1/2 on all cars. I changed the thermostat, it was broken, this did not fix the problem, it is still doing the same thing. Is there anyway to tell if it is the fan or one of the sensors, or maybe something else.