Truck runs fine. Its cold out so im blasting the heat and thats working fine. But my gauge drops to C when its on. So I turn the heat off and it goes right back to normal. it never goes past normal reading temp. Im pretty sure its not a bad thermostat cause my heat would be wierd. Just wanted to know if maybe its one of the plugs on the thermostat housing

-2001 4.0

 

maybe the thermostat is stuck open, if you have a scan tool look at the temp readings. it could be a bad sending unit but i doubt it.

 

I would think if the stat is stuck open it would always run cold. Maybe the wrong stat? What temp stat is in there now. I had the same issue until I changed to a 195 stat.