Hello,
My Mother has a 2004 Monte Carlo LS and recently the temperature gauge started to rise around the 260 mark, so we replaced the coolant, thermostat, ECTS and bleeded out the system as well. It was fine for about two weeks and then it started to rise again.
Even when just starting the engine up while its cold the temperature gauge will go above 260 and now the gas gauge is acting funny.

I took a picture I will try and upload it somehow but any help will be greatly appreciated! I put it as an attachment.

-Thank you!

 

if other gauges act up, it could be a bad cluster. I don't know exactly how this can be tested, but I had issues with the gauges in my '96. The speedometer would say "0" when moving at a decent rate but fluctuate around "30" when sitting still.

 

Hmm, Thanks for the input.
So I would have to replace the whole instrument cluster? I would get the 180$ Cluster off rockauto and then replace it?
-Thank you

 

It could be the cluster, I failed to read the post before commenting, you could try the gauge cluster, stepper motors go out in the clusters resulting in inoperable or inaccurate gauges.