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모델 A1225 / Mid 2007 and Early 2008 / 2.4, 2.8, 또는 3.06 GHz Core 2 Duo 프로세서

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Graphic card overheating, CPU fan in full speed, then black screen

I am a newbie to Mac and this forum, so please be gentle.

I recently acquired an early 2008 iMac A1225, EMC 2211 - 2.8GHz CPU, ATI Radeon 2600 pro graphic card, 320GB HDD, 24" 1920x1200 LCD.

It turns on with no problem. In around 10 minutes, the cpu fan runs in full speed (loud and noisy). GPU temperature reaches 128 Celsius degree in 10-12 minutes, and follows by black screen. CPU only gets 32 Celsius degree at the same time. As the computer is idle. Youtube video definitely speeds process, especially full hd videos.

Previously, Mac OS 10.8 installed. After reading some posts about similar issues, I tried to change it to 10.6, but got black screen after erasing the OS (no os now) during installation.

Things have tried:

- reapply GPU thermal paste using arctic silver 5

- kext tricks (10.6.2 as suggested by others)

- reset smc, pram

Update: I was able to reinstall 10.8 but not 10.6. Thermal paste seems to be working - heat sink reached 128 celsius degree while GPU die at 111 celsius degree. Previously it was reverse. However, the overheating problem is remained.

This iMac is virtually a stylish 20-minutes-iMac. It has a overheating graphic card and can not do anything.


I am answering my own question:

The only way to permanently fix the symptom is replacing the video card. I can confirm this because I just replaced my video card. I do not have GPU overheating issue any more. I have been watching full HD online movies for several days (stress test for the card), the overheating issue is gone. The highest GPU die temperature is 61C, normally it is around 50C without online videos. Before replacing the card, my old card can easily reach 128C in completely idle. I have been trying many ways to fix the old one, however none of them worked. Ways I have tried:

- replacing GPU heat sink compound

- adding an extra heat sink to GPU

- removing air wall under GPU

- reflowing GPU (the GPU died after this, don't try)

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Hello gbuyer! I am experiencing the exact same problem you were experiencing, but replacing the graphics processor did not help. Both cards get extremely hot when installed. When you bought a new graphics card, did it have the heat sink attached to it already? I am starting to believe it's actually my heat sink that's bad! If you could reply to this comment, I would greatly appreciate it! Thanks!

I'm merely continuing to comment because I am discovering more about my problem. I just replaced the whole logic board, and I'm STILL experiencing the issue. Now I believe it's either the power supply or something about the actual iMac casing that's shorting out something. Fishy stuff here. I'll continue to update in case anyone else has these issues too and can't fix them by simply replacing the graphics card.

It is the gpu heat sink

they can get small leaks in the copper tube and stop working properly

I have the same issue on at MacBook Pro mid 2015. Screen goes black after 10min of restoring TimeMachine backup. I downloaded the HWmonitor sensor for Mac and it show the "GPU Die overheated"! Just bought the Mac so it will get returned!

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Your machine shipped with system 10.5.2 (9C2028). You can get a replacement disk from Apple for $16 plus tax and shipping, just give them your serial number. Use this disk to reinstall the system and run AHT to try to determine if the GPU has failed.

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I was able to install 10.8 using the original hard drive. iStat reported 61 Celsius degree when I turned on the computer from cold, after 7 minutes, it reached 95 Celsius degree, at the meantime, CPU kept at 33 Celsius degree. Something wrong with the video card or power supply, I think. Please help.

I am talking about the GPU (video card) temperature. 61C->95C in 10 minutes from cold start. It is not normal.

More information:

The temperature should be over 128C as it seems 128 is the highest value iStat menus can report.

MxM current kept increasing in idle, from 0.6A - 1.4A, temperature increased in the same time. Please note that the computer was completely idle while these happened.

12V S0 dropped a little bit 11.89 -> 11.82. Don't know if this is a faulty PSU or GPU.

Please help! Thanks!

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Okay you guys! After months and months of trying, I have found the true solution to the overheating graphics card. I was right with my initial hypothesis. It was indeed the heat sink.

I was mislead for months because the heat sink I purchased initially to test my theory was also malfunctioning in the exact same way. But after isolating literally EVERY part in the iMac, buying a new logic board, and purchasing 5 new graphics cards (without heat sinks) to no avail, I finally decided it must actually be the heat sink, and it absolutely is.

I believe the failure is relatively common or the heat sinks are pretty easy to damage because it is rather surprising that I would purchase one and have it malfunction in the exact same way. So, when you get your heat sink, be sure to handle it gently! It might just break the same way.

It's incredibly uncommon for heat sinks to fail in general, so it really surprises me that this did turn out to be the solution. But I suppose there must be a weakness somewhere in the design of this heat sink. Not sure if it's a very minute leak that eventually releases all the coolant in the copper pipes or if it's simply a disconnect of the different components that make it up.

Either way, the solution is simple: if you have the aluminum iMac 24" overheating problem, don't go out of your way to buy an expensive graphics card. It's likely only your heat sink that needs replacing.

Now, regarding gbuyer's experience, I can only assume his new graphics card came equipped with a new heat sink. They usually do if you buy them off of eBay. If his DID come with a new heat sink attached, I'm willing to bet that the new heat sink fixed the problem, not the new graphics card. (Please, gbuyer, correct me if I'm wrong).

But that's what I've got to say on the subject. I bought a whole other iMac to make sure the heat sink really was the issue, and after swapping GPUs and heat sinks back and forth and fixing both iMacs, it is absolutely certain for me that the heat sink is the cause of this problem.

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Just how can you tell if the heat sink is defective?

If your iMac is experiencing the overheating problem EXACTLY the same way ours have, than experimentally (and extremely expensively) the cause has been proven to be the heat sink. Sorry Mayer. I know it's not a very promising response, but my 8 months of work on the subject and my hundreds of dollars spent on the problem has proven to me beyond reasonable doubt that the heat sink is almost exclusively the problem.

Also, the experiments have been proven by sheer numbers. My two iMacs would experience the problem when the heat sinks and graphics cards were swapped and now Kevin can back me up on this assertion. :) I apologize for my use of "than" in the comment above. Should have been "then," but I'm on my phone and can't correct it. Haha

Thanks for your clarification Tommy.

what is good temperature range for 24 in iMac 2008? With fans running at around 2K rpm, I get low-mid 30s C, but it is very noisy. I don't think it was very noisy until last few years. Temp sometimes gets into 40s, so I bump up fan speed, using an SMC app.

Also, how hard is it to replace the heat sink? Is soldering required, etc.?

Hoping to get a few more years out of the ol clunker, for basic apps, movies etc.


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Many many thanks for your research into this subject.

I've just replaced the heatsink in my iMac and the GPU is now running at the right temperature.

My heatsink had a split in it causing the GPU temperature to go up and up. After a few minutes, the screen went black. Simply swapping the heatsink for a replacement fixes the problem. No new GPU required.

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Yay! I'm extremely glad my extensive work on this particular problem has benefitted someone! Haha congratulations on getting your iMac running properly again!

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Thanks for sharing this, I am pretty sure what the problem is. The heatpipes are (well, actually Were) filled with some kind of liquid. I took the whole iMac apart and at first cleaned all fans and heatinks. Also, I tested every one of them if they were working before assembling the system again. They all did. But, when I put everything together and booted, the temperature rose gradually until it was around 104 degrees Celsius. So, took everything apart again, and cleaned the heatsink processor and memory from the old thermal goo.. Applied silver paste and assembled. During aasembly, I saw some strange discolorations on my motherboard. Looked like some dried up liquid. After looking further, I also found discoloration on one of the heatpipes, but did not draw the right conclusion yet. Until I found this movie on youtube. https://www.youtube.com/watch?v=qXso8KFG... Then I was sure. The heatpipes have lost some kind of liquid and the discolorations were dried up liquid. Also, I did find the hole in the heatpipe, exactly with the same discoloration seen in the video. So The heatpipes are the problem. Also the guy in the movie tells that the heatsink was not hot, so I tested this on my system, and I have exactly the same issue. The heatsink of the GPU is not hot. So the heat from the GPU is not transported through the heatpipes to the heatsink and therefore it is not properly cooled.

Now, I am looking for a replacement heatsink, or I will actually try to repair it. I will try to find out what kind of liquid was in there, and how to get some back in there. And then maybe solder it. I will report back about that. Hope this helps anyone.

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Indeed, Marcel, after my extensive process of elimination that I went through, if 2007 iMac owners are experiencing such symptoms, it is most likely the heatsink, as you too have concluded. Many props to you to looking into actually repairing a leaky heatsink! I was aware of the liquid-cooling design that Apple uses and that the reason the heatsink was broken was likely because some of the coolant had escaped (despite the lack of any apparent physical evidence on mine). I wish I could tell you what kind of liquid they actually use and how to patch up the copper, but I'm afraid I have little to no information on the matter. The Power Mac G5 had a MASSIVE radiator-looking heatsink that was notorious for leaking its special liquid coolant. I'm not sure if it's the same stuff, but that might be a good place to start looking if you ever wanted to go back and repair your broken iMac heatsink. I believe there are various guides online that detail repairing a Power Mac G5 heatsink. Thank you so much for your input!

Yes the heat pipes are filled. When we had a few systems over heating we found pin holes in the tube! One way to tell which heat sink is good is to weigh them the heaver one is the good one.

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Does anyone know a seller where I can purchase the heatsinks alone? It appears that they are usually bundled with the Radeon 2600 HD Pro card.


Hey guys. So I think I might be extremely lucky. I opened up my iMac and gave it a good cleaning. There was a ton of dust in the fans. After I put it back together, its been running very stable and not overheating.

If anyone is going through the same problems, they might want to clean out the dust and try that first before buying any replacement parts.

Thanks again for your help guys.

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Howdy Clifford and Raul!

Unfortunately, the heat sinks alone are very hard to come by. I got lucky and found one guy selling them on eBay, but I'm pretty sure I bought the only ones available when I did the repairs. One of the ones I bought was from someone in San Diego, and that one turned out to be broken. The other one I bought was from some other guy on eBay, and it just turned out to be working. In terms of knowing any sellers that I can trust, I hate to say it, but I don't know anyone when it comes to buying these heat sinks. I would just make sure I could return the item if it turns out to be bad.

The other option you might have is looking up broken Radeon 2600 HD Pros and seeing if they, too are bundled with their heat sinks. You might be able to get a working heat sink off of one of those. The risk with that, though, is that you probably wouldn't be able to return the item if the heat sink turned out to be bad because it was a broken item to begin with.

Good luck guys!

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I ask the same question as Clifford. Where do you buy the heatsink alone and if you can't what is a reliable source where you can buy one that you can trust.

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Howdy Raul! Take a look at the comment I left under Clifford's post. If you have any more questions, I'd be more than happy to help in any way I can!

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I bought my heatsink from Mac2MacOnline at http://mac2maconline.com/

Give them a call, they're really friendly.

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Thanks for the info guys. I'll give those options a try.

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Hi I think yhe best way is to just buy a new heatsink. I have an iMac 20" (2007). I found a heatsink for around 35 euro's (just look for one on Ebay (I looked for: imac 20" heatsink)) (including shipping, not sure about tax) So I will order this part... I think that differs a LOT in costs compared to new video card. So, before buying a new video card, check your heatsink like I did and save some money! Hope this will help someone someday...

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And I also agree with your post here, Marcel! haha

Though they are difficult to find, the heatsinks are dramatically cheaper than the GPU card. I went through purchasing a number of GPU cards thinking they were the problem at first, but was very relieved to find out that the inexpensive heatsink was the only thing I actually had to buy! As I recommended above as well, I think it might be easier to find heatsinks attached to broken GPU cards rather than separately. You run the risk of buying a broken heatsink with it, but I believe that very few people sell the 24-inch iMac heatsinks separately from the GPU card. It seems the 20-inch ones are a bit easier to find on their own.

One can buy heatsinks all over ebay, also for 24"iMac. I found these very easily and did check the sellers rating and positive feedback. One can find type number on the plate attached to the CPU/GPU. (In my case, it was "730-0479"). The heatsink works without any issues since I bought it... :-)

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