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Yes, these methods work!
Authored by: Cyndi on Jul 14, '11 09:09:36AM

I have an iMac, 2.16GHz, Intel Core 2 Duo running 10.5.8. 24". It's given me all sorts of trouble, probably because I bought it used off Craigslist. A few months ago my HD had a catastrophic failure. I replaced it and things were okay. I noticed the top left hand corner of the screen (as felt from the back) was often hot but had no other symptoms until the HD started failing. When I added RAM a few weeks ago I started getting new problems (timing could be coincidence, I don't know).

Black lines on the screen, as another commenter had. Messed up graphics here and there (pixelated, overlapping, program screens not going away after switching programs, also blank menus after clicking with the mouse or blank popup menus). And lots and lots of crashing (rainbow wheel of death, mouse moved, but nothing else worked and I had to power down). Running Disk Warrior and also Disk Utility (including booted from the OS disks) didn't help. Activity Monitor did not show high memory or CPU use.

Finally, I realized the crashing was correlated with how hot that back corner was. Even though my house air was in the 70's, I had to turn off the computer to cool down several times a day. And I crashed 2-4 times a day. It slowly got worse over time and it was this bad only a couple of weeks.

I installed Temperature Monitor (freeware:;1 ) and discovered that all of my temps were high (except ambient air) but the worst was the Power Supply. 185*F/85*C!!

Next I installed smcFanControl (freeware:;1 ). I upped all three fans and within 5 minutes I had normal temps through-out the computer. I've been experimenting a bit with the fans so thank you to this author for giving suggested settings.

Now my power supply is 127*F/53*C and everything else is even lower. It's been about 24 hours and I only turned off the computer overnight. No crashing, no graphics messes, no black lines. Crossing my fingers that this is the answer.

As for other suggestions: I'm not using an external fan and I'm glad I don't seem to need it. When the hard drive died, the repair shop cleaned the inside of the case (and they did the same a few months before that when I had to replace the screen). My air flow around the iMac is not blocked and it's not hot in my office (no A/C but the house is well insulated and I'm in a temperate zone).

From reading other forums it seems that iMacs overheating is a common problem. Even when you don't get symptoms, it shortens the life of your HD and other components. I have no idea why Apple's fan settings are so off and why they don't tell people about this problem and why they make it impossible to know about or fix without 3rd party software. But thank God for freeware developers and experimenters everywhere who figure this stuff out.

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