I thought the same thing so I popped the 160 Tstat out and tested it in a pot of hot water, thing works great. My water pump is brand new as is my motor. Its a fresh build with 200 miles on the motor. I made some improvements like #302 swirl port heads with a ton of head work, Lunati cam, stiffer springs, double roller timing chain, and also installed a 2500 stall.
This is my first time having a mechanical water temp gauge so I'm not used to seeing exactly what my motor is doing. In the past I gauged hot by a certain point on the stock gauge, now I can properly see what temp I'm at.
The radiator in the car is the original stock one so I'm guessing 40 years old? Guys at Champion said to start off with the rad and go from there.