73 C10 temperature gauge climbs past 250

[jontsa]

My 73 C10 temperature gauge started recently showing that my engine is overheating. I checked coolant levels and left the car idling. In 5-10 minutes the temp gauge was showing over 250F degrees The car was running fine and no signs of overheating. I had a new 195F thermostat left over so I replaced that, added coolant and left the engine idling. Again in 5-10 minutes the temp gauge had steadily climbed from cold up to 250F.

I tested the temperature sender with a multimeter. When engine was cold, it was showing around 1000ohms. I started the engine and the ohms started dropping steadily reaching about 100ohms at which point thermostat opened and meter stayed at 100-110ohms.

Do I need to find a new temp gauge or could it be something else?