My HDD recently failed on my 2011 iMac running High Sierra (the most current OS possible for this year). I'm retired and didn't want to put forth the money for a new computer so I took it to a local repair shop see if they could replace it. Their reply was there was too great of a chance to damage the screen by replacing it (I'm assuming they don't have the right tools or just aren't very knowledgeable about older iMacs). I live in a colonial mountain town in southern Mexico so my options are limited. They proposed using an external SSD drive instead. I didn't see any issues with that so gave the go ahead and they installed High Sierra on it. Now I'm home with it starting the process of reinstalling files but after 10-15 minutes of use the fans are running all out. Experimenting I restarted and just let it sit without starting up any programs. After 10-15 minutes the fans are running at full speed again. Going by the Activity Monitor the top user of CPU is kernel_task and the little bit of research I did indicated that this is associated with the fan issue. The question is why? What could be causing this and is there a way to correct it?
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Hard Drive issues on a Mid 2011 iMac
- Thread starter BisonJump
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Not sure if this is your issue but I have a 2010 27” iMac and when it’s HDD died I swapped in and SSD but when I did I no longer had a way for the temp sensor for the HDD to monitor the temp so the fans ran full blast at all times. I ended up downloading this and I have been running it for over 6 years without trouble
Mac Fan Control
Mac Fan Control
If you are otherwise happy with the performance of the external drive (is it USB?), you can use the link from @iSightG5 and use Macs Fan Control to have it control the fan speeds.
As for the reason of the fan speed, there could be many different reasons why.
There is a temp sensor in the OEM HDD, and maybe the whole drive stopped working including the temp sensor.
Maybe the HDD, while failed, is still spinning and generating a crazy amount of heat, causing the fan speed to ramp up.
If the repair shop opened your Mac, maybe they disconnected the SATA cable to the HDD, which would also disconnect the temp sensor and in turn would cause the full blast fan speed.
This is a ten year old computer, with ten years of dust built up inside and in the fans itself, maybe causing the fans to ramp up to keep up with the cooling.
Maybe something else or some combination of the above.
Someone with a little knowledge electronics, the tools, and can follow directions could probably do it 45 minutes the first time.
As for damaging the screen, this could happen, but only if someone does something really stupid like drop the display or just starts ripping cable connectors out without following directions.
Macs Fan Control is good to adjust for the HDD temp sensor missing/not connected, but if the fan speeds are ramping up due to heat, it won't help you.
As for the reason of the fan speed, there could be many different reasons why.
There is a temp sensor in the OEM HDD, and maybe the whole drive stopped working including the temp sensor.
Maybe the HDD, while failed, is still spinning and generating a crazy amount of heat, causing the fan speed to ramp up.
If the repair shop opened your Mac, maybe they disconnected the SATA cable to the HDD, which would also disconnect the temp sensor and in turn would cause the full blast fan speed.
This is a ten year old computer, with ten years of dust built up inside and in the fans itself, maybe causing the fans to ramp up to keep up with the cooling.
Maybe something else or some combination of the above.
They just don't know how to do it. It is really (relatively) easy and I can do it in literally 5 minutes using just two suction cups, a T10 driver, and T8 driver.
Someone with a little knowledge electronics, the tools, and can follow directions could probably do it 45 minutes the first time.
As for damaging the screen, this could happen, but only if someone does something really stupid like drop the display or just starts ripping cable connectors out without following directions.
It is hard to say what the problem is without doing some tests, but I would check out the iFixit guides for HDD replacements to put in a SSD. It really isn't hard.
Macs Fan Control is good to adjust for the HDD temp sensor missing/not connected, but if the fan speeds are ramping up due to heat, it won't help you.
I would suggest you change the SSD yourself.
Tools you will need: A set of torx drivers (T6, T8, T10 are needed)
View the below videos several times, until you have thoroughly understand the process, what to note and what is the risk in each step.
Better yet, doing the iMac opening with the video in front of you.
Alas with that model when an internal hard drive is replaced one needs to install a heat sensor kit otherwise the fans take off like a Jumbo Jet.
You can try using MacsFanControl for internal and maybe external drives. Download from here and do not buy gthe Pro version as yet:-
crystalidea.com
You can try using MacsFanControl for internal and maybe external drives. Download from here and do not buy gthe Pro version as yet:-
Macs Fan Control Download for macOS & Windows (Boot Camp)
crystalidea.com
Thats crazy, and they call themselves a repair shop?
There are 10yr old's on YouTube demonstrating how to upgrade HDD in these beautiful old iMacs.
Buy a torx set and do it yourself, take your time, watch some guides.
Your fans are ramping up because the OEM drive is dead, the old drive itself has the temp sensor integrated.
Do as @Nguyen Duc Hieu suggested and install SSD internally.
After installing the Macs Fan Control it showed that the only fan that is ramping up is the one associated with the dead HDD. I turned it down using the custom settings and after monitoring it for 2 days I don't see any of the temps rising unusually so I think that will take care of it. Thanks.