You are going to want to set that fan up to come on at 210-215
At 180 it would be on most of the time.
I use the thermostatic controlled electric setup, and have it set to where the fan will come on at 210 and shut back off at 190 and I'm using a 180 thermostat. (I don't have a Hemi)
But notice the temp span (210) and the fan comes on.
(190) it's cooled down to normal temps and the fan shuts off.
Normal driving around 30mph and up, the fan never comes on becuase the airflow keeps it under the temp that the fan is set to come on.