I recently installed an SSD into my iMac and downloaded "Macs Fan Control" which works perfectly fine.

However, when I plug in my external monitor via Thunderbolt, the GPU temperature increases for 10°C (50°F) to about 55°C (131°F) or something which I think is normal. Due to the temperature increase, the RPM of the ODD fan (which I use to cool the GPU) also increase to a hearable amount. (about 2000 RPM)

I use following settings for the ODD cooler:

  • Sensor based value from GPU Diode
  • Temperature that fan speed will start to increase from: 45°C (113°F)
  • Maximum temperature: 70°C (158°F)

Can or should I tweak my settings (increasing the temperature that fan speed will start to increase) without the risk of damaging the GPU?

  • From what you described, "Macs Fan Control" isn't "working perfectly" as you describe. This is because you're not getting the correct values from the SSD sensor which affects the SMC's "calculation" the temp and what needs to be cooled. See this related post: apple.stackexchange.com/questions/257268/… This software only overrides what the system is trying to accomplish.
    – Allan
    May 25, 2018 at 16:31

1 Answer 1


55c is not really going to hurt your gpu or your iMac but cooler is always better some people have added a sensor... The other thing is the thermal paste apple used was terrible on all those older iMacs... If you haven't replaced I would definitely do that as well, some of the machines I've played with, the thermal paste was no longer doing anything...It's not really complicated and there are a lot of video guides available if you need them...I would redo cpu and gpu at the same time... That will give you a noticeable reduction in temps...Then when you get your fans set up properly, you should get another drop in temp plus a drop in noise, and probably add a few more years of life to your system. I use Kryonaut thermal grease just a personal preference but there's lot of good stuff out there. the other thing that will help is a good cleaning if it hasn't been opened in a few years... I hope this helps, I really hate typing.

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