Sending Unit for Temperature Gauge

Harbor freight has the infrared heat guns as noted above for about $25 on sale sometimes. That will tell you if the temp gauge is accurate.

The sensor is a good place to start. A lot of antifreeze will come out when you take it out. You can drain it first or just swap it fast. If the sensor doesn’t fix it, it can be lot of trouble to tear into the dash.

Are your fuel and oil pressure gauges accurate? If not it could be the dash voltage regulator.

Mine has aftermarket oil & temp gauges, that might be an easy way out if you really want the accurate readings.