recently had a blown head gasket repaired and had headers installed while this was all apart. now i get an intermittent check engine light with a p125 code. the temp gauge needle never moves above 1/4 of the way up the scale.

could the headers cause it too run cooler or would the repair and new parts (thermo, water pump, fluids) all combine for this condition?

thanks

 

thermostat could be opening too soon

 

This could be something as simple as low coolant or a bad temperature sensor. Could also be a bad thermostat as indicated by djfllmn above. When you installed the new thermostat did you use the temp thermostat as specified by Ford? It is also easy to end up low on coolant when you totally drain the system due to air in the system. I would check coolant first.

 

Just an FYI, I have installed a brand new thermostat before that was bad right from the beginning. It was stuck open, causing the engine to over heat, but that was in the summer time. If it was winter, it probably would have kept it cold.