Lawrence,
I think you've got an ISC350 in your coach. The following is based on my experience with a 3126B rear radiator coach. From what you related, it sounds like you probably have a 185-190F thermostat as that is the temperature range you indicated running at mild outdoor temperatures and on a relatively flat road. Your coach has a rear radiator so your fan is driven directly off the engine and thus its rotation speed is linked to engine RPM. Cruising in 6th on a level road with minimal headwind and moderate outdoor temps, 185+- a few degrees sounds normal. Add a headwind and outdoor temps around 100F you will notice the engine temp climb to the mid 190s or above. Downshift to 5th to increase engine, fan, and water pump RPM and you will see engine temp moderate. Grade climbing will also raise temps quickly. Climbing a steep grade in summer temps can result in a check engine or over temp condition. I'm not sure about the ISC350, but my CAT 3126B alarmed at about 225 if I remember correctly. Key to climbing grades with a direct drive fan is engine RPM. I would take the coach out of cruise control, apply increased throttle and downshift as needed to keep the RPM close to 2000. Watch your engine temp on the Aladdin or Silverleaf and downshift accordingly. Don't worry about speed. Leave the tranny in the lower gear until speed reaches a point where the tranny wants to upshift. Then go up 1 gear. only. Your goal is to manage engine temperature, not speed.
So, IMHO normal temps would probably run 185-193. Climbing you'll see 195-205/210 depending on outside temps. If you get to 220 you are getting very close to an overheat condition.
Climbing with side radiator coaches is different as then you want to manage engine torque since the fan speed is driven by a hydraulic motor and not the engine.
Steve
