Chosen Solution

It looks like the temperature sensor in the iMac for the hard drive if now gone in the teardown - can iFixit confirm? If it has gone, this is great, as now I can add and remove a hard drive without Apple’s specifications for a temperature sensor built in, like in 2009 and 2010 iMacs.

I switched out the hard drive on a 27" 2011 today and I can confirm that the hard drive sensor that attached to the drive is gone. I put in a Seagate 1 TB SSHD and it’s running just fine. No modifications were needed.

Y splitter cable works if you are upgrading to SSD. I don’t know why Dan keeps recommending OWC cable. maybe kickbacks from OWC. it’s overpriced and meant to take advantage of naive user. more info about this sc*m can be found here https://www.youtube.com/watch?v=pMsk1o1W…

Thanks Hanno for this hint! It should be noted here that on the SATA side of the cable the wires 1 and 4 have to be shorted (and NOT wire 2 and 7). This is much easier then Apple’s official solution where you have to take the iMac almost completely apart. For better understanding I have added below some (low resolution) photos. (Sorry for the bad quality). CAUTION!!! This modification is ONLY VALID when you switch to a solid-state drive (SSD). DO NOT use this mod to connect a normal harddisk drive! This will most likely result in massive overheat of your iMac.

The correct way of dealing with this is to use this: OWC In-line Digital Thermal Sensor for iMac 2011 Hard Drive Upgrade. This has proven to be the best way to handle the sensor issue which ever drive you put in.

I’ve been reading this thread and the Y Spitter solution. I am 100% sure this is just grounding the temperature sense data pin 11 on the sata power plug to the hard drive. These sata power splitters and the connections on a standard ATX power supply tend to be be wired with 5 x 3 sets of pins bridged together. 3.3v , gnd, 5v, gnd, 12v. The 3 pins 10, 11, 12 in one of these splitters are all grounded. Maybe grounding this temp sense pin 11 shuts the fan up. I wonder what apple do in the late 2012+ models when it is a blade only SSD only model with no standard drive. My other reading implies that in the pre 2012 models there was a blanking jumper plug that was sometimes put in the unsued sata power port to keep the SMC happy with no drive present. Standard sata power wiring.

Sorry if this has been answered I just thought my thoughts may be useful to anyone stumbling across this tread like i did.

I suspect you are right, the splitter Y cable is the easy choice. If you are handy with cables you can also just isolate the grounds and accomplish the same thing but the splitter cable is the easiest.

I just installed a 480GB SanDisk “SSD Plus” in a mid-2011 iMac (with no external thermal sensor on the old drive). I’ve booted from an El Capitan installer flash drive, formatted the SSD, and am installing El Cap as I write this. No fan noise at all so far. I’m hesitant to clip wires on the power cable, so I’m really hoping my luck holds! If the fans start roaring when booted from the new SSD/El Cap, then I guess I’ll have to try P J Sch’s technique… The weird thing is that I feel like I’ve swapped drives in other 2011 iMacs (possibly early-2011?) that still used the sensor cable, and therefore require the OWC part that Dan keeps recommending above. I have, and was prepared to use, that part, but there’s no place to plug it in on this model! Learn something new everyday, eh? I hope so at least!

I changed out the stock Barracuda 1GB drive after failure using a new 4TB Seagate drive with a 256MB cache. The fan was maxed out once I replaced the drive. I use a software solution, namely TG Pro, that allows the User to control the fan speed. The app also monitors numerous temperatures. Works like a charm.

Has anyone had screen blackouts once they’ve installed a new SSD in to an iMac mid 2011? the computer continues to work but the screen blacks out quite often, it works again once it has been re-seated, but not for long.. ‘the screen does not show anything when shining a torch on it

Is there anything new on this topic? I have read, that the fan issue with Third-party-drives (esp. SSD) in 2011 iMacs has gone with a SMC-update on High Sierra. So there should be no OWC thermal cable or short out required, because fan speed is controlled by S.M.A.R.T. Can anybody confirm this? Thanks for your help!

I’m planning on changing out HDD for SSD on Mid 2011 model. Just wondering if a short SATA power extension cable will ground out the temp sensor wires like Y splitter cable as I’m curious how they could be electrically different.

I think I sorted it out. I soldered 100Ω resistor into pin 11.

HDD fan spins at 2500rpm, machine works like a charm and no need to install any software

So Dan, just to make sure, here is my situation. I have a 2011 21.5 inch iMac. It had a 3.5inch 500GB hard drive, which died. I plan on fixing the machine, but I am somewhat on a budget. If I get a normal hard drive or hybrid drive (SSHD) then I should get the OWC cable with it, because Hard drives generate a decent amount of heat. However, if I replace the broken Hard Drive with an SSD and used a 2.5-3.5inch adaptor, then I wouldn’t necessarily need the OWC thermal sensor because SSDs (especially just a 500GB one that I am replacing) don’t run as hot as normal HDDs. So because of that, I can get away with using a short block or using the Y adaptor, because that is what even Apple used (right?) Thanks!