I have a 2004 Chev Impala and the temp guage went way past any numbers and wasn't hot. The speedo also stayed at 30 mph went the car is stopped. The speedo started working again when I shut it off and restarted it but the temp gauge did not.

plugged catalytic converter

Check the temp. switch the one that goes to the guage either a bad switch or a short in the wire.

temp door is bad and needs replaced you can just see door motors under dash by gas pedal

Thanks for choosing FixYa and welcome. Do you have a check engine light on? If it was ran a lot during the overheating, there may be engine damage. You may have a bad head gasket.

We had the same problem with '04 Chev Impala speedo. It's fairly common so I'm told. Mr Whizzard Technical Services does a great repair job for a very reasonable price. I believe it was about $179CDN plus cost to ship to him. Price included return freight. You can call toll free 1-888-803-8523. Google him for more info. While it does mean the vehicle is down for a while, but we were very pleased with the quick turn-around (about 10 days).
Mike J, St Albert, Alberta, Canada

There are two things that would cause this a bad coolant temp sensor or the guage is bad, this cars had alot of problem with the cluster, the gauges would do crazy things the most common would be the fuel gauge and temp gauge, i would start by replacing the coolant temp sensor and making sure the wiring to sensor is good and not frayed and touch any metal, hope this is helpful.

don't drive it .
You have problem with cooling system , if you keep driving it like this , may cost you an engine.

Unless you replace the water pump you are going around in circles. When you drive you have the natural air-flow thru the radiator and water circulastion will occur ie hot water rises cooler water sinks. If you havn't already damaged the cylinder head your lucky .White gooey residue on dip stick or oil filler cap will be an indication of this. Rust colored water indicated the adsence of inhibitors or coolant fluid and internal corrosion will be a consideration .

could be but more like the engine computer plug is lose or corroded

about $450.00 should fix this speedo.they are having a problem with speedos sticking. the cluster will have to come out for repairs. is you car covered under any extended warrantys ?
good luck Chris