Ford Repair: Overheating?, cracks in the system, hail dents

Question
Sam
My 2000 Taurus has always run great, and last year after a crack was found in the coo;lant resovoir the whole cooling system was flushed and checked with a new thermostat.
We recently had a hailstorm that smashed out the back window. Until it can be seen by an insurance adjuster in a few weeks, I taped plastic over the back opening.
Shortly after, I noticed the  coolant warning gauge showed the car was overheating after long drives on the highway with the air on.
Would this have anything to do with the window missing, possibly forcing the cooling system to work harder and overheat? Or is it unrelated? Everything seems fine-no leaks, lots of coolant with a good color, etc.
In case it is related I think the adjustor should know, because combined with the hail dents he might write it off.
Thanks!
P.S. Very hot and wet up here in Saskatchewan last few summers( usually dry and mild), and summers are getting longer. Maybe we are getting U.S. climate! Must be global warming? ;-)

Answer
Bud, the reason for the over heating is not the window, is the coolent cracks.  Typically, when you flush the system and relpace with new clean coolent.  The old coolent would have enough dirt to plug a small cracks in the system.  Now, since you're using a clean coolent, it does not have enough dirt to plug the fine cracks.  I would recommend to fix the cracked coolent resovoir.  Thanks!