If you haven’t installed the needed thermal sensor you’ll need to do that [https://eshop.macsales.com/item/OWC/DIDIMACHDD11/|OWC In-line Digital Thermal Sensor for iMac 2011 Hard Drive Upgrade]. Using fanControl software doesn’t really work that well and your system will not last as long.
Your system likely needs a bit of dusk cleaning after we see the TG Pro snapshot we can get into wants needed.
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=== Update (02/24/2019) ===
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I don't see any issues with the thermal sensors. So SMC is encountering a different issue. I'm suspecting you damaged one of the ferrite beads (L5500 through L5531) near the sensor connectors on the logic board.
If you haven’t installed the needed thermal sensor you’ll need to do that [https://eshop.macsales.com/item/OWC/DIDIMACHDD11/|OWC In-line Digital Thermal Sensor for iMac 2011 Hard Drive Upgrade]. Using fanControl software doesn’t really work that well and your system will not last as long.
Your system likely needs a bit of dusk cleaning after we see the TG Pro snapshot we can get into wants needed.