You should verify these temps with a IR gun...sender could be bad.

Especially, if you had no boiling over of reservior at 242.

 

Sounds like you may have air in the system. Best thing to so though is to refresh the system with a brass propeller water pump, heavy duty fan clutch, and inline thermostat mod. Its not cheap and it takes some work. But if you want to cut the bull**** that is the stock cooling system, this is the way to do it. Your headgaskets will thank you for it, and live longer with idle temps never hitting 200 on a normal day.