HDD thermal sensors

HairyFool wrote:

Does a 21.5" IMac (Late 2013) have a thermal sensor on the HDD?

Yes. If you replace the hard disk drive, whatever you replace it with must include that thermal sensor.

The two options are more RAM or an SSD. As she is not a power user I doubt if the RAM upgrade would add much but from experience a SSD can have a significant effect.

You're probably right about that.

It's very easy to determine if your Mac's performance is being limited by available memory. Please read Check if your Mac needs more RAM in Activity Monitor - Apple Support. If the "Memory Pressure" graph is frequently "red" your Mac would benefit from additional memory. If not, it won't. It's that simple.

Nope. There was a firmware update back in... 2016? that removed the need for a custom thermal sensor from 2012 and newer iMacs. Today thermal sensor cables are only needed on 2011 and older models.

However I would suggest instead setting up an USB 3.0 SSD as an external boot drive. USB 3.0 is almost as fast as SATA III and will save you the time and effort of opening up the iMac.

HWTech wrote:

padams35 wrote:

Nope. There was a firmware update back in... 2016? that removed the need for a custom thermal sensor from 2012 and newer iMacs. Today thermal sensor cables are only needed on 2011 and older models.

I've never heard anything about this. In fact several users recently complained about the fan running at high speed after replacing the original internal hard drive so I think the sensor is still required. AFAIK, OWC still is providing the sensor adapter with their SSD upgrade kits.

OWC may still sell that sensor, but they don't include it as part of their 2012-2019 iMac upgrade kits anymore. https://eshop.macsales.com/item/OWC/K21IM12HP1TB/#includes

A firmware update, possibly at the same time as the SSD/APFS modernization, is the most logical explanation I can think off for why OWC originally felt the need to make a thermal sensor that is no longer required and would also explain how searches turn up fan issues shortly after the 2012-2013 releases but nothing recently. I tried searching, but the only recent fan speed issues I could find were either unrelated to HDD replacement or related to 2011 and older models.

A third option with less chance of creating a basket case, is to run the iMac from an external USB 3.0 SSD.

see > Use an external SSD as your startup disk … - Apple Community

FWIW most any USB 3.0 external SSD or DIY USB 3.0 enclosure and 2.5" SATA SSD will work with that iMac.

An SSD will definitely give the biggest performance boost even if the hard drive is still healthy.

If you opt for an external USB3 SSD, then make sure it supports UASP as well for best performance (I don't know if any of the off the shelf externals support this protocol).

Interesting. I know they still had the temp sensor adapter included in the kit since I looked it up sometime in the last year (probably close to a year ago). Very strange Apple did that....so unlike them.

padams35 wrote:

Nope. There was a firmware update back in... 2016? that removed the need for a custom thermal sensor from 2012 and newer iMacs. Today thermal sensor cables are only needed on 2011 and older models.

I've never heard anything about this. In fact several users recently complained about the fan running at high speed after replacing the original internal hard drive so I think the sensor is still required. AFAIK, OWC still is providing the sensor adapter with their SSD upgrade kits.

HWTech wrote:

I've never heard anything about this.

Neither have I but none of my recent Macs have hard disk drives so I can't be 100% certain.

"recent" = since 2010 or so