Fan runs loudly with excessive rpm's

[wendpick]

I have been battling with fan speed on my iMac recently.
I installed iStat which shows normal temps, but the fan revs up to 4000rpm - for seemingly no reason at all. Sometimes its quiet for long periods. It sometimes helps for a while if I put the machine into Sleep mode, but then I hear the fan start to rev up again when I resume activity.
I have spent hours with tech support, who then upgraded me to a higher level of tech support. But still the problem continues.

I would like to ask members of the Noisy Fan Club 2 questions.

1- Have you recently upgraded from Leopard to Snow Leopard. Did the problem only start then?
2 - Have you tried booting up into Safe Mode and seeing if the fan speeds up while you work in Safe Mode?

My fan only started this behavior after upgrading to SL, and I am now running in Safe Mode with my fan totally,blessedly silent at 1198 rpm.
I would be interested if anyone is having similar issues?
Has anyone found a clean install of SL helped? Or going back to Leopard maybe?

 

[Klainn]

I had this same problem which eventually led to my getting a replacement imac.

To narrow it down, run the extended diagnostic from the Install DVD disk 1 (hold D just after power up). It will likely come back with something like "4M0T/2/40000004: HDD-1374"

It's probably either the fan is bad or the logic board is jacked. If you've moved the machine recently it could possibly be a lose cable from the fan to the board, either way, it's likely a trip to the apple store for a repair.

This has been my experience, yours may be different.

 

[i7QuadCoreMania]

I highly doubt the problem is related to upgrade of Snow Leopard.

I suspect one of your temp sensors are failing. if you have installed istat do you notice one of your temp sensors going in and outing out when the fan revs up?

Did you do the apple hardware test? i.e. insert apps disc, reboot holding 'd' run the test and see if there are any errors.

from my experience it should come back with an error code if one of the sensors are failing.

I have seen the fan rev up to full speed due to a loose temp sensor. If you are under applecare then take it in, if not, run the test and check for a loose or bad temp sensor.

 

[wendpick]

Thanks for your help

I had this same problem which eventually led to my getting a replacement imac.

To narrow it down, run the extended diagnostic from the Install DVD disk 1 (hold D just after power up). It will likely come back with something like "4M0T/2/40000004: HDD-1374"

It's probably either the fan is bad or the logic board is jacked. If you've moved the machine recently it could possibly be a lose cable from the fan to the board, either way, it's likely a trip to the apple store for a repair.

This has been my experience, yours may be different.

You were right - I ran the diagnostics and it did come back with an error code similar to the one you mentioned.
So I am off to the Apple store.
I really appreciate the replies to my desperate post. The fan was driving me crazy.
Thanks again!