engine temp gauge doing strange things
I have a 05 F350 6.0L and while driving after about 10 miles the engine temp gauge drops to the cool zone and the check gauges come on and the tow lite starts to flash also. Could this be a bad thermostat or a bad sensor? I also checked the fluid level and strenght and it is ok. Anybody have this problem before?

Steve

 

Part 1 -How to Test the Thermostat (Ford 3.0L, 3.8L)

Part 1 -Troubleshooting P0117 and P0118 ECT Sensor Tests (Ford 3.0L, 3.8L)

It sounds like a bad temp sensor, but it would be better for you to test both possibilities.