My manuals for 1.5 ton Chevvys is to run 160 stock and if a heater is installed use 180.
The gauge will bounce around but should stick right around the t-stat set point unless idling for a long time, going up a hill (high power output, low forward speed for cooling).
When you turn off the motor is most likely will shoot up to 200+ unless you idle for a few minutes to let the motor cool.
