Way back to the initial postings...perhaps a correction...
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"Q: WHAT CAN I DO TO PREVENT MY 360 OVERHEATING?
A: Just use common sense, really. "
At times I'm not sure common sense has ever helped an XBOX360 problem.
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"Don't keep it on for hours on end, there's no reason to have it on for more than 5/6hrs in one sitting. "
This is not absolutely not true.
An XBOX will get up to it's max temp in short order if playing a game and all 3 cores are online. From that point forward it stay a constant temperature and will never get any hotter unless the fans die, dust bunnies grow too big, or the room temperature/humdity perhaps changes drastically. Obviously longer you run any electronic equipment the more chance there is for it to fail but don't overheating will be the result.
Also, How could you possibly know there is no reason for having the XBOX running more than 5/6 hours. Don't try to apply your standards upon other gamers. I have run my XBOX(s) for close to 16 hours a day every day since since November 2006 playing music, playing movies, playing games, or just sitting at the dashboard and have never had a failure relating to overheating.