2001 Oldsmobile Silhouette Car overheats then cools down

Car overheated yesterday, or at least the red light came on that said it was about to overheat. I pulled over, let it sit a few minutes - no more than 5, started it up again and it was fine. It did not reheat again while out earlier in the day. Got out in the evrening to drive it, it did the same thing while waiting in line at a drive thru, I revved it, and it cooled down, and stayed cool the rest of the evening. This morning, same thing again. Started to over heat, I turned it off before it got the red, waited - and now it doesn't overheat. Had mechanic check fluid levels in radiator while getting oil changed yesterday and he said levels are fine. He said perhaps the thermostat was stuck and granted I know very little about vehicles - the thermostat seems to be working fine. I'm wondering more about a fan, secondary fan or perhaps a fuse.

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