having trouble getting cooling fan to come on at high temps(210-220) I have changed the sensor on the engine at the crossover pipe and still nothing. The fans good if i jump it or just unplug the front sensor the fan runs. I even jumped hi and low speed and it worked ok. I have heard there is a sensor on the back of the pass side head that is tough to get to. I am pulling engine this weekend to replace head gaskets and long tube headers. Just thinking if there is a sensor on the rear of head now would be the time to replace it.