dropping of temperature gauge while driving?

thank you, i don't think it is problem of thermostat.... because everything will come to normal when removing battery wire and return back!!!!

l have the same problem in my gmc envoy please any answer

Problem is resolved after replacing the coolant temp sensor the one on the back of the motor on the passenger side and the thermostat also must be replaced. (when I replaced the thermostat only the problem remain the same so you need to change both!).

Thanks! That's exactly right. I needed that. I was stuck. Cisco Parker

I have changed the thermostate and problem solved

How did you get to the sensor

the one that was at the back of the engine ... please see the attached photo

If you can fix it by disconnecting the battery or by resetting the P0128 error, then it's not the thermostat. It's not likely the ETC either as the OBD reader shows the raw temp at 176 while the gauge is zero'd (pegged 100 deg). When error is cleared using OBD, gauge immediately goes to 176, so ETC is being read correctly.

I am facing problem of dropping of temperature gauge while driving. It comes automatically after some hours during driving. Moreover, once temperature needle goes down to zero during driving, Airconditioning COOLING system also stops working during that period. then it come back to normal ....then i changed the thermostat and the tempreture coolant sensor i faced new problem that the needle of tempreture gose up and down and the the rpm getting high please help my car is chevy tb 2008