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MacBook Air 2011 i7 wrong fan reading;

My Macbook Air (Summer 2011, i7) tends to think it's running way hotter than it is, and permanently ramps up the fan. Closing the computer and reopening resets the mistaken sensor, but I'd rather not have to do this half the time after I open the computer.

I'm using Fan Control for the temperature reading.

As others have said, the fan in the Late 2103 MacBook Pro Retina is very quiet. If you are wondering if your fan is broken there are actually two big tells that are easier than listening for the fan. For one, if your Mac gets very hot from high CPU, as long as the temp sensors work the CPU clock speed will eventually get clipped when it overheats and will run at a fraction of its normal clock speed making even the most lightweight apps move glacially. System process like smon will seem to take up all of the CPU in the Activty Manager because the system processes are queuing and waiting on CPU cycles that never keep up. I noticed that when the machine cooled down and was starting cold, it ran well for a little while until it got too hot and the problem would repeat. I discovered the problem in detail after buying iStat Menu for $9.99 from the App Store which is a must have regardless of your situation, but in this case it gives detailed sensor data on temperature and fan RPM. When I was seeing the CPU sensors getting up near 200F the fan RPM was reporting at around 6K, a speed I can definitely detect with my ears, but it was dead silent. It is normally quiet but when it’s maxed out its loud. Since the temp kept climbing and then finally clipped the CPU clock again, I concluded the fan was dead. The controller thought it was running at a stated RPM, so while the signal to the fan was indeed telling it to spin at a certain speed, it wasn’t. This was actually a good thing because replacing a fan is an easy job that you can do with a $20-$40 replacement fan, some skill, the correct (but hard to find) set of tools, and the iFixIt guide. If the sensors were not giving readings or clearly inaccurate ones, or the fan was not showing any rpm even when it was radiating heat, the problem would be with the motherboard- either with the fan controller or the sensors, which basically means a new motherboard. That’s bad. Since the sensors are imbedded in the board, even warranty breakers with soldering irons will not get this one, just hope that iState gives you readings a normal machine would, but the fan simply isn’t powering on as that is the easy fix.

The other bonus with iStat menus is that it graphs every metric so you can watch trends to get a better idea of what “normal” is. Again, this is a superb tool well worth the $10 that actually runs much leaner than the Apple Activity Monitor while giving you a lot more functionality, though it is not a replacement as it does lack detailed process control. (It does list top processes in each category.) I thought my computer was simply wrecked by something as the speed issue persisted after a system rebuild, so I concluded it was hardware and it was done. I then read about the fan sensors and realized it wasn’t running even though it was desperately hot, I am happy to report she’s as good as new now!

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