My MBP keeps shutting itself down. It seems to be temperature related, since the computer seems to stay on longer if it hasn't been turned on for a while (and won't boot up for more than a second right after it shuts down). I talked to an Apple repair guy on the phone, and he seemed to think it was the logic board, but after reading around, I don't completely buy it.

This thing does have a history of temperature problems; AppleCare replaced some parts in it after some heat-related shutdowns 3 months after I bought it. I have checked the hard drive and battery, both are fine. Anyone have any ideas?

This would happen 3 months after my AppleCare warranty expired....

Thanks in advance!

Do you hear the fans kick on at all?

Generally overheating problems can be the fans, a faulty temperature sensor, or the logic board.

The fans are spinning, and my RPMs are increasing with demand, but that is sort of spotty. From the looks of things though, my GPU heatsink is throwing off some odd temperatures; it usually stays right at 69C, but occasionally it will drop down to 8C or jump up to 135C, or anywhere in between. It seems odd; obviously the temperature can't be jumping around that rapidly. CPU temperature is steadily rising, but hasn't gotten over 50C. All of the other temps look fairly normal - staying at or below 40C. From a cold start (off all night), the laptop will run for around 20 minutes, then auto-shutdown. Then it will not boot for over a second until I let it sit for awhile.

I really do think this is a heat issue, and it appears to be a sensor that isn't letting the machine know it's running too hot. It seems that the fans are working, they just don't know when to work. Is this something I can fix with a solitary part, or is the GPU heatsink sensor integrated into the logic board?

EDIT: The fans are consistently staying within 50rpms of each other, and they vary from 2300-5500rpms. I'm using iStat Pro for these figures.