Chosen Solution
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. ==============Update================ 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)
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.
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.
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.
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.
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. Update 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.
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.
I bought my heatsink from Mac2MacOnline at http://mac2maconline.com/ Give them a call, they’re really friendly.
Thanks for the info guys. I’ll give those options a try.
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…
