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Question: iMac 27 late 2009 overheating critically

I have recently noticed higher noise with the fans of my iMac (couple weeks ago, all of a sudden). When installing the Macs Fan Control 1.4.10 I was really surprised, how high the temperatuers inside my iMac went. When the fan control in each part was set on "Auto", the HDD fan was running at its max speed of 5500 RPM. Even though the temperature did not go under 51C (i.e. still the full speed of fans - heavy noise). Other temperatures (CPU, GPU, PSU) a reaching even higher.

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When I set control of the HDD fan based on CPU Core 1, the fan noise went down, however, the SSD temperature went up on 55C. Other controlls went down, though.

User uploaded file

Which temperature values are most important? Is it better to have SSD temp higher ot the other ones?

iMac Pro, macOS High Sierra (10.13.3), 2,8 GHz Intel Core i7, 8 GB DDR3

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Mar 12, 2018 12:03 AM in response to ondrejfromnitra In response to ondrejfromnitra

1. An iMac that old, is likely to be full of dust and needs to be serviced.

2. The HDD fan cools the HD, the CPU fan cools the CPU and GPU, the Optical Drive fan cool the SuperDrive area.

3. While speeding up the fan in one area helps cool that area, it usually has a negative effect on the other areas.


If you think that you are having overheating problems, then the iMac should first be serviced and clean out before you start altering any of the fan speeds.


If you do feel the need to alter the fan speeds. Then it is better to slightly increases the speed of all three fans a few 100 rpm, than it is to just increase the speed of one fan.

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Question marked as Helpful

Mar 12, 2018 12:03 AM in response to ondrejfromnitra In response to ondrejfromnitra

1. An iMac that old, is likely to be full of dust and needs to be serviced.

2. The HDD fan cools the HD, the CPU fan cools the CPU and GPU, the Optical Drive fan cool the SuperDrive area.

3. While speeding up the fan in one area helps cool that area, it usually has a negative effect on the other areas.


If you think that you are having overheating problems, then the iMac should first be serviced and clean out before you start altering any of the fan speeds.


If you do feel the need to alter the fan speeds. Then it is better to slightly increases the speed of all three fans a few 100 rpm, than it is to just increase the speed of one fan.

Mar 12, 2018 12:03 AM

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Question: iMac 27 late 2009 overheating critically