Loud iMac Fan: Quick Guide on Solving This Issue

iMac Fan location
iMac Fan location

Image source from ifixit.com

Intro to solutions for loud iMac fan issue

Here’s an example of an iMac with a fan spinning uncontrollably:

iMac Fan location

This is a 21-inch iMac from mid-2011. This model has three fans: one for the CPU, one for the hard drive, and one for the optical (DVD-ROM) drive, each having its own fan. The most common fan problem with this iMac model is the hard drive fan sensor going haywire hence causing the fan to spin at full speed and creating annoying noise similar to an aeroplane jet engine.

Other causes that could make the iMac fan spin at full speed?

Apart from a faulty fan or sensor, another common reason for the fan spinning at full speed is a severe overheating issue with the processor or graphics card. To check if any applications (software) are pushing the CPU to its limits hence generating excessive heat, click here for a guide on monitoring your Mac’s CPU usage using Activity Monitor.

Another potential cause could be the need to service and replace the thermal paste on your Mac’s processor and graphics card. Over time, this paste can dry up hence affecting performance. For more details on the role of thermal paste, click here.

How to check fan spinning speed?

By default, your Mac doesn’t come with fan control software or heat temperature monitoring tools in the macOS system. Therefore, if you want to control the fan speed, you’ll need to download a third-party app for that purpose. Fortunately, there are a few excellent apps available for this task and one we recommend is Macs Fan Control. It’s both free and user-friendly, in fact just download it and drag it to your Mac Applications folder.

What is considered an abnormal iMac fan speed?

If the fan speed remains constantly at 2000 RPM and above, there’s an issue.

Current RPM Speed

In older iMac models with three fans, the hard drive and optical bay fan can be manually set to a constant 1000 RPM, while you can adjust the CPU fan speed using the settings below.

iMac CPU Fan Controller Setup

Here’s an example of how to set up the fan controller software for CPU fan:

Launch the app

Macs Fan Controller

Select the Sensor-base value then select CPU Core (average).

Macs Fan Control Temperature Range

Temperature selection between 45C to 95C.

Finally, click on preferences and select the option Autostart minimize with system.

Conclusion to loud iMac fan issue

For example on average, your iMac’s ideal temperature range should be between 40°C to 50°C. When it’s under heavy load while you’re working on it, the temperature should not exceed 100°C. If, even after using the temperature controller subsequently your iMac continues to frequently overheat, it might be a good time to have it checked by a Mac computer specialist.

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