I certainly didn’t want to open the thing back up so I went with a software solution. It therefore ran the fan speed at 100% all the time. My new drive had no temperature sensor on it, so my iMac motherboard didn’t know what the HD temperature was. The Hard Drive that Apple uses from the factory has a proprietary controller on it for reporting the drive temperatures to the motherboard. When I booted up the new install, the iMac fans went crazy. A few years ago I installed a new 1TB Hard Drive (spinning SATA).
