Engine Temperature gauge on 2005 Jeep Grand Cherokee

When idling in park or stopped at a light the temperature gauge begins to slowly rise indicating that the vehicle is beginning to overheat. So far I have found no apparent radiator leaks or hose leaks and the radiator cap is cool to the touch. I can hear the radiator fan begin to rev high when the gauge begins its climb. As soon as the vehicle is in motion the temp drops.
Any suggestions would be appreciated

Asked by for the 2005 Jeep Grand Cherokee
Need to know what ENGINE you have first!! Makes a difference as to what info. to give you.
1 more answer
Operating temp of an eng is 79 deg if its going above take the radiator for flashing some of its cores are blocked