temp gauge wacky

my metro has been running great but ive noticed when im driving that the temp gauge will run it self almost into the red and then it just drops back down to normal again i dont even have to start moving down the road . im wondering if the thermostat is hanging up or if its a bad sending unit to the gauge

i have this same problem sometimes, it will just jump around after going up near the red. Should we Just replace this part? is there any other suggestions?

I am currently having this problem also. I see no on ehas answered it. I have replaced within the last year:

Radiator, Upper radiator hose and another smaller hose close to it, coolant temp sensor, thermostat, and water pump.

I wonder if my thermostat is correct or I need to replace it again? When I removed it, it had no paper gasket but I put one on with the new thermostat. Was this the right thing to do?

You could have an air pocket in the system. Try bleeding the system with the heater on and see if that helps.

How exactly do you bleed the coolant system?

keep the heater on warm all the way to the right that runs the coolent to your heater core and let car idle then try high way driving for 10 min or more at 6o mile but make sure before you start the car ,you have enough coolent,if that didn,t work then check for thermostat it might be working ok but if there is rust change it ,because it might have the hard time to fuuly open or close because of the rust,and of course you want to fully flush the systembefore outing new thermostat,another reason could be small leak around the gasket at thermostat housing which cause sending air to system