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Best way to cool your iMac Desktop Macs
My iMac killed its hard drive the second year of use and then the entire screen/graphics card and logic board had to be replaced at the three year mark. It unfortunately began to misbehave again shortly thereafter.

I use mine to run a 54" Bravia HDTV as the extended desktop and use EyeTV and noticed numerous graphics errors lines, and failures to refresh the screen during overheating bouts. I observed that the upper left hand corner of the iMac has some sort of an air pocket that traps extreme heat from the graphics card there. (The rear-viewed 'right' of the top air exhaust slot).

This top left hot air pocket-trap seems to be due to negative cabinet air pressure interfering with natural heat convection on the left side; heat collects there but just can't get out! The fans are part of the problem and just don't help at all.

To verify this, I installed a small temperature probe in the back top left hand (from the front) side of the back air exhaust slot (right side viewed from rear) around 20 cm (9") from edge. The usual temperature reading there runs around 130F (54C!) and often (always during malfunction or addressing error graphics lockup-freeze) exceeds a peak-hold temperature of 140F (60C).

At first I mistakenly thought forcing cooler air into the bottom might reduce this but it does not. There is an air pocket there caused by the vacuum back-pressure of the internal fans, which are all trying to suck air in through limited air inlets, and blowing out the upper right side of the slot so heat just accumulates there and it just runs away

The correct and ideal simplest way to permanently fix your overheating 24" Imac (iMac6.1 iCore 2 Duo at least, and several other models) requires two fixes.

First download and install smcFanControl 2.2.2. Set it up to provide (still quiet) minimum fan speeds of 2200 rpm for the HD and 2800 rpm for the CPU, leave the Optical Drive fan at 600 rpm to minimize dust accumulation (or just tweak it up if/when you will be using it much)

Next obtain a 12 vDC enclosed squirrel cage fan like the San Ace B76 - you need not buy a new one nor this particular (best) model, but any enclosed suction-blower fan of this type (rather than an open blade straight exhaust) is ideal. It shouldn't cost much at a surplus shop. Get and hook it up to any common 9vDC/AC adapter (around 10 vDC) to run it cooler and more quietly than full 12v speeds, since it is now sucking heat instead of blowing cold air.

Tape it (with clear boxing tape) to the rear left corner of the back (3" from the side) so it sucks air out of the hottest point of the back slot and blows it away upwards.

Your iMac will now be fixed - the air slot temps will seldom ever exceed 106F (40C) again (even under heavy graphics use) and your graphics card will stop cooking.

Barring other serious dust or other heat sink assembly issues, your iStatNano display should now (roughly) read (degrees C): (at 26C Ambient room temperature)
  • HDD 42
  • CPU 33
  • GPU 40
  • GPUD 46
  • GPUH 38
  • Amb 26
  • DVD 1 39
Always blow out your system with a vacuum's air exhaust hose by blowing air pressure into the back slots and the small round center air exhaust under the desktop stand (to reverse-flow and force air and dust back out the bottom intakes) with power off once every six months or so to keep the air passages clear. Suction alone (out the bottom) does not do such a good job, and may actually draw dust further into the machine if used from the top at the heat exhaust slots.

[crarko adds: I haven't tested this one. Has anyone else needed to do something like this to prevent over-heating? If so, please post your experience in the comments section.]
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Best way to cool your iMac
Authored by: hexeric on Jun 07, '11 08:05:27AM

i find this much better: (settings here also work for boot camp/win7!)

and yes: unfortunately, an imac (just as an macbook) definitely needs cooling. the HD and GPU fans are as good as not adjusted by heat sensors. i do a lot of video work on my new imac (quad core) and keeping the minimum fan speed of both, HD and GPU (it's controlled by the DVD drive fan interestingly) at 2000rpm is sufficient. CPU is monitored by the application and the fan adjusts automatically.

further: my old iMac (v2007,1) got black stripes on the display due to the heat issue - you know, when the diffusion skin in front of the LEDs gets a little burnt...

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Best way to cool your iMac
Authored by: bluescreen on Jun 19, '11 11:05:32AM

In rasterized video display generator systems stationary 'stripes' (like boxes) are generally indicative of either memory array (draw buffer[s]) or output array write, read or output addressing-counter failures. In such 2 dimensional flat 'table' arrays, each row and column location (and blocks of the same) is/are formed of data applied at numerical x-y addresses.

Each numerical 'x' or 'y' (row or column) range of addresses represent some vertical or horizontal 'stripe' range, as any specific 'block' represents an intersection of the coincidence of those two ranges of addressing-counter regions. The lowest numbered physical address (start) is in one corner and the highest numbered address (end) is at the diagonally opposite corner of the stored or drawn 'x-y table array'.

In a (more simply described for example) simplified base-10 example, addressing-counter numbers are generally formed/generated by some sort of a serial to parallel decoding array that reuses the 'fine' 0-10 or 0-100 (hottest, fastest, hardest-working 'fine' address-counting) counter by merely occasionally incrementally adding a 'coarse' 10-100, 100-1,000, 1,000-10,000, 10,000-100,000 (etc) 'bit' to the address-count output to get it up to the higher address-count location-range numbers. Repeating 'stripes' are thus indicative of a (repetitive) failure of the underlying 'fine' address-counting numbering decoder.

If the 'fine' (0-100 ex) decoder starts missing it's ability to generate addressing numbers, say for example, from '50-100' during each count-up sequence, then the array will be striped (empty of data) in equal stripes all the way up the range, since those array locations cannot be addressed to be read, rewritten or output.

Stripes don't indicate a failure of the display, they indicate a failure of the display's own controller/driver circuits, the GPU or the graphics card's output or the display's input/output interface.

Otherwise the failure to refresh, redraw, erase or move a moving or movable block of data like a program window or animation graphic element within it (a so-called 'sprite-block' of local image data) or deal with it's overlay-depth-priority or transparency (box-trails) is a problem in the RAM addressing, rewriting or data manipulation/flow handling of the GPU (or data or software instruction) itself.

Since modern low single voltage DRAMs don't heat up like their older progenitors 90% of these sorts of (non-defect) failures are voltage or thermal parallel addressing counter/connection related.

Edited on Jun 19, '11 11:11:59AM by bluescreen

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Best way to cool your iMac
Authored by: montylee on Jun 07, '11 08:25:57AM

I have a 20/2.4/320 iMac that has overheated twice, resulting in Applecare repairs. It always runs hot, so I am going to give this a try. The last repair the Apple tech said iMacs run hot, which does affect surrounding components.

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My brand new iMac overheats too
Authored by: lullabud on Jun 07, '11 09:38:56AM

In January I got a brand new iMac 27" (pre thunderbolt) iMac. It has been having serious heat problems, especially in windows, and I have seriously been thinking of how on earth to get it to run cool.

The worst problems I have are in Windows 7 when playing video games. I have to set smcFanControl to max out fans, then reboot to Windows or else the system will lock up. (Yeah yeah, I should have Apple look at it, but the only reason I got this new one is because they had my 24" iMac for a month across 3 different repairs! I don't want to go through that again.)

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My brand new iMac overheats too
Authored by: bluescreen on Jun 10, '11 03:46:59AM

On mine the most common (like three times a day nuisance) happened on the external desktop Sony Bravia (1080p) screen when running EyeTV and any web browser with flash video. If I tried to maximize (full screen) any Youtube like flash vid the system would freeze, lock up, get persistent HD video-line drawing or windowserver refresh errors and/or throw/log invalid address out of range errors.

In most cases the power switch was the only way out and the external thermometer always showed me 60C or more at the upper left air slot location. If you are getting 60 air that means the board has to be 70 and a few 10 more degrees above that, solder turns liquid.

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Best way to cool your iMac
Authored by: brucio on Jun 07, '11 10:01:15AM

How hot is too hot for internal components in general? I thought 130 F was within acceptable limits.

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Best way to cool your iMac
Authored by: bluescreen on Jun 15, '11 09:48:28AM

130C is fine but 160C at the air exhaust is bad news. This temp means that the boards and components are 10-20C hotter (than the measured air temp) at some point or other, and since heat rises it accumulates upwards of (above) the standard internal temperature sensors.

Most all of these common motherboard internal on-board (diode), on-chip or on-die (NTC/PTC) temperature sensors are not designed or intended for gauging temperatures accurately for vertically oriented operating measurement situations. This means that the temperature at the center or bottom edge pins of a sideways standing chip or pcboard is not the same as the temperature at the top of the component or top edge of the board when it's standing up on edge instead of laying horizontally.

While it takes around 330C to fully liquify modern SMT solders, solder is very soft and it tends to get mushy at much lower than full (liquifying) melting temperatures.

This means that surface mount components, which are where the heat comes from, can expand and push this now "mushy" solder away from their expanding pins/pads during extremely hot bouts. Once this solder layer is pushed away by the expanding component legs it cannot reflow back into good contact again, and at some point, cold solder heat-stress joints will eventually develop, where they were fine before.

Constantly sucking this excess heat out of the left-top air slot keeps the upper region thermal runaway at bay, by constantly removing heat from that obvious hot spot and staying ahead of the heat build up instead of waiting for a temperature rise and then trying to cool it off later.

The larger San Ace B76 suction/blower fan I recommended can be run at as little as 6 vdc in total silence and seems to work just as well at that voltage and there's no need to drill any holes nor do any damage to the iMac case. One or three little pieces of common boxing tape will effectively hold it there to the top slot behind the iMac where it is invisible from the front, and it's cooling effect will stop the tape from weakening or slipping off from this hot spot of the cabinet.

If you don't have or use A/C in the summer, you might prefer to use an adjustable "universal" AC adapter (3-13vdc) that you can turn up on hot days to run the fanat a variety of speeds, instead of using a fixed (6-9 vdc) voltage one. Be careful though, the (nominal) "10~12 vdc" San Ace B76 "stalls" at around 4 vdc, where it may continue to spin (very quietly if already running), yet won't start up on it's own. 5.5 vdc is the lowest typical starting/running power/voltage/rpm you can get away with on it.

If you cannot locate a San Ace B76, Nidac offers a smaller "Gamma 26" 12v model that's a bit lower in air flow, thus a bit noisier at lower power/rpms, but is a good substitute. Any small side suction dc blower fan exhausting upwards at the air slot is better than having none, though YMMV.

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Best way to cool your iMac
Authored by: Anonymous on Jun 07, '11 10:46:41AM

Get a HEPA room filter. Open the windows. Jeez, just vacuum once in a while.

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Best way to cool your iMac
Authored by: leamanc on Jun 07, '11 04:47:55PM

+1 Insightful.

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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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Best way to cool your iMac
Authored by: bold_seagull on Feb 13, '12 01:07:55AM

This has been a useful fix, and the SMC fan control has (for now) stopped the intermittent freezes.

I have a couple of questions though;

1. Is it worth opening up the iMac (late 2006 20" in my case) and giving it a thorough blow out getting rid of all the dust, or is opening up just as likely to cause other problems?

2. Could anyone post a pic showing the additional suction/blower fan mounted to the rear vent slot of the machine? I'd like to see whats involved prior to giving this extra solution a go.

many thanks

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Best way to cool your iMac
Authored by: bold_seagull on Feb 13, '12 04:07:02AM

I've just bought one of these which I figure I can mount onto the back of the iMac case, with the fans drawing air away from it. Hopefully this will help, and at under 5, worth a gamble.

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Best way to cool your iMac
Authored by: mpillischer on Sep 04, '12 07:02:54AM

Hi all,

I had this same problem with my iMac getting unbelievably hot to touch on the back top of the computer (front as well, but really blazing on the back). After some research and thought, coming from the brain of a computer-phobic non-techie, I decided to see if I could solve the problem by hooking up some additional fans to cool the computer at the back. I don't mean taking apart the computer of course, just adding some additional air flow behind it.

I totally solved the problem for about $65-70, no messing with computer settings, no taking apart the computer, no AC unit installed behind my computer (although I thought about this).

I run lots of programs at once, lots of windows, lots of music, and lots of videos, so it's going to get hot. I got some of these belkin laptop coolers: .p?id=1218501938631&skuId=4635326&st=Belkin%20Cooling%20pad&cp=1&lp=2
My iMac sits directly under a shelf, so I was able to hang 3 of these so the fans hit directly on the top back of the screen (see pics below). I looked at all the brands at BestBuy and this seemed like the cheapest best one, and wanting a fast solution to this I just bought one to try it. When I plugged it in to the USB and fel the pathetic little fan I thought to myself, "you're kidding me, this is a piece of crap." But I tried it anyway, and it really cooled it off. No more serious heat. It was still how on the left and right sides since the fan only rested on the computer in the middle. So I went back and got two more, and got a USB splitter (you can usually find these at Marshalls for like $5) so three fans only take one USB port on the computer.

I am so happy with these Belkin cooling fans, and this really saved my computer, that I am going to post this everywhere I can find. This is a really nasty problem to have to deal with, and this is a good cheap solution for even no-techie types. It doesn't look too bad either, but I could see some people who are obssessed with how their mac looks not liking these cheap-o laptop-coolers crowding its style. Oh well. Trust me, it works!

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Best way to cool your iMac
Authored by: wizbang_fl on Sep 04, '12 05:52:01PM

SMC Fan Control helped a lot. I had been told the metal mac cabinet on the new iMac's was intended to act as a heat sink. Wondering if you attached some sort of cooling device to the outside of the cabinet (like a water cooler) if you could get a more effective solution rather than just moving around air.

I routinely open up my Desktop / Laptop every year to blow out dust, dirt, etc that has been sucked in. It's more than I would have thought would accumulate in a year, but with a cat & dog even their hair gets sucked in.

Yes, it takes some time, but we have an '06 iMac (gave to my spouse last year) that still runs circles around a lot of my friends Windows laptops that they've only had a year. Had my iMac 27" just over a year, but I haven't had a chance to open it up yet.

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Best way to cool your iMac
Authored by: tjwu4 on Sep 28, '12 12:11:29AM

I'm using gel type of ice pack wrapped with towel and just tape on the back of my imac. It seems to work to keep it cool. This might be another way that can work.

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Best way to cool your iMac
Authored by: fgduncan on Aug 31, '13 03:48:59PM

24 inch iMac Early 2008

My iMac had always had a hot upper left corner, as I have found all iMacs do. Recently I had started having the computer reboot in the middle of a job and the corner was so hot that you felt uncomfortable touching it.

This worked absolutely fantastic!! Downloaded the fan controls and adjusted them as recommended and 5 minutes later the computer was very much cooler and temps are even lower than those shown. Downloaded istat nano and now have an instant check on the temperatures, although I obviously do not need that anymore.

I was amazed to find out that not only were there fans inside the iMac, but that the computer knew exactly what their speed was and, in addition, could control them. Another surprise came when I found that the computer has temperature measuring devices inside of it.

I would highly recommend following the directions given here since applying external cooling to an internal problem is not fixing the problem at the source. These two programs are free and easy to use, so using external cooling is a waste of time and money.

The only complaint I have is istat nano is in degrees C and not degrees Fahrenheit, but I can learn to live with that.

Mega kudos to the author!!

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