Overheating onset

[Tom Donohue]

Just looking for some suggestions regarding a problem that popped up
Saturday a.m. on my 91TQA.  I was in the Boston suburbs for a wedding.
 Drove out from Western Mass. Friday, about a  2 hr. drive, with no
problems.  Then on Saturday, while poking about Chelmsford, the temp
gauge began rising and set off the chimes and the red display.  Stopped,
checked coolant level, which was fine, as was fuse #15.  When I headed
back down I-495 to the hotel, the temp came back to slightly higher than
usual, and all warnings disappeared.  Sunday, did a little driving
around, keeping an eye on the temp gauge, which remained volatile, then
headed back home along 495 and I-90.  At speeds between 80-95 (and
sometimes even a little slower!), the gauge remained at normal levels.
 When I got off the Pike at Exit 1, and began driving in town traffic,
it began climbing again.  While driving at steady 40 or so, the temp was
no problem.  When stop & go began, the gauge climbed again.  I've
narrowed the problem in my mind to a bad fan thermoswitch or a bad fan
motor.  Since there was no sound associated with the failure, I'm
leaning toward the thermoswitch.  Anyone have any other suggestions?
 Anyone ever made the repair?  Thanks for any help or suggestions.
 Regards, Tom