Bob,
Heed HrL, not me.
However, for what it is worth: most thermostats are rated at full-open temperature. Circulation coolant should start earlier: a 180 thermostat might start opening at/before 150/160 degree. If your cooling system/radiator/engine-coolant passages are clean, your temperature should hold at 180 (except at idle or at low-speeds&RPMs).
