Thermostat or not

Never trust a 40 year old gauge. Get a non contact thermal temp gun and verify the actual temp it is running. My Cuda is an example of how far gauges can be off. When the temp is 180 degrees the gauge is all the way over on the lat line. I tried a new sender and still shows the same so the factory dash gauge is just wacko. And I agree with the guys that a thermostat is needed.