Temp guage overheated than stuck ...is it broke or??

[parboy721]

My 41 flathead plym p12 special deluxe overheated and overflowed out of radiator at idle today after 15 minutes.  I Fill 2 inches below cap line .. Temp gauge maxed out than stuck at high end.... is there a fix or did I break it. Any experience on this. Temp should run between 160 to 180 I have read. 50/50 coolant mix non pressure cap thermostat 160 or 180 I have a new pump and a flushed system...running too lean possible....altitude is 5000 asl  in Colorado.??Thanks if anyone can help... My granpappy passed and I lost the brains of the old school mechanic.

[Jeff Balazs]

Here is a few things to check for. Sometimes loose debris can collect at the thermostat and block or partially block flow here. Another thing you can do is check to see the thermostat is working properly. You will need to immerse it in hot water and a good thermometer to verify temp it opens at.. Chances are if your car has lived at this altitude for a while then the timing is probably OK and the carb has been set to run at altitude. If you just got it then you need to check your manual for these settings.

Jeff

[Billy6]

 "Never trust a new thermostat". I installed two in a row on my 40 Plymouth and they were both bad. I learned to always test a new thermostat in hot water with a meat thermometer before installing.