iMac fans spinning up and down

[mutuz]

Hi all.

I have had problems with the fan on my 2012 iMac for the last week. The fan spins up to more than 4000 RPM, then goes back to 900-1000 RPM for a while, and then returns to above 4000 RPM again.

This is happening despite the Mac idling. I have been monitoring the fan and temperatures for the last week, see the two screenshots below. The temperatures are stable around 26-45 Celsius and CPU is 90% idle.

I tried resetting the SMC, but this did not change anything. What can I do to further troubleshoot? Any suggestions would be welcome.

 

[nambuccaheadsau]

If this is the 27" model, have you replaced the hard drive at all?

 

[mikehalloran]

If this is the 27" model, have you replaced the hard drive at all?

Same goes for the 21.5"

The spinners are now 6 years old. Average age for them to have cooked to death is 5.

Can it be something else? Well, yes but any tech is going to look there first.

 

[mutuz]

Same goes for the 21.5"

The spinners are now 6 years old. Average age for them to have cooked to death is 5.

Can it be something else? Well, yes but any tech is going to look there first.

This is the 21.5" with a fusion drive. Maybe, but should this fire up the fan to maximum RPM? Besides, I hear no noise from the magnetic drive indicating a failure is imminent. I've Time Machined the drive anyway, just to be sure...

 

[mikehalloran]

Besides, I hear no noise from the magnetic drive indicating a failure is imminent.

You won't. If you can hear the drive failing, it's long past dead.