One of the cooling fans in my PC (there are several) is starting to give up. I think it might be the bearings that are giving up, but whatever the cause, every several minutes, it visibly slows down for maybe a minute or two (slows down to the point that you can actually see the individual fan blades as the fan rotates) and makes quite a bit of noise, then it gets back up to speed and runs smoothly (and quietly) until it decides to get slow and noisy again.

The main purpose of this fan is to be one of two drawing in fresh air through the front of the case, and provide airflow across several 7200 rpm HDDs.

I have already ordered a new fan, so this is not a question of whether it should be replaced. I expect to be able to actually replace the fan by the second half of next week.

Rather, my question is: aside from the fan itself failing at some point, is it in any way an electrical risk for the other hardware in the system to keep the fan running? In other words, assuming I can live with the noise, should I disconnect the faulty fan while I wait for the replacement to arrive (and accept the fact that the HDDs will be running hotter, which is clearly suboptimal), or is it acceptable to get as much utility as possible out of this fan while it lasts or until the replacement arrives?

  • My guess is no, but any answer is opinion based so this a bad question.
    – DavidPostill
    Jun 10 '16 at 20:27
  • @DavidPostill Could you please elaborate on how this question cannot be answered by facts or specific expertise (your claim that "any answer is opinion based")? It seems to me that the question as asked should be perfectly well answerable; either a fan can (or will likely) cause some form of additional hardware damage when it fails, or it's unlikely that it does. Both alternatives could be reasoned about based on knowledge of computer design and electronics. (I assume that you read the full question before voting to close, rather than just the question title.)
    – user
    Jun 10 '16 at 20:48
  • "is it in any way a risk for the other hardware in the system to keep the fan running?". The answer can be yes, no or some %risk somewhere in between. Without knowing the details of how the motherboard and other heat sensitive components have been designed it is impossible to give a conclusive answer.
    – DavidPostill
    Jun 10 '16 at 20:55
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    When I read this question it wasn't clear if you were asking whether a failed fan could cause electrical damage to the rest of the system, or whether the reduced cooling capacity could cause some other component to overheat. I guess the former, based on the answer you accepted. A good answer to the latter requires more information about how your cooling system is designed.
    – gatkin
    Jun 10 '16 at 21:20
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    @gatkin Yes, I am asking about electrical risks. Hopefully clarified that in the question; thanks for the feedback. (Short of the HDDs running a little hotter, the system should have fully adequate cooling for all major components even without this fan. I added the fan that is the companion to the failing one specifically to address high HDD temperatures. The failing one came pre-installed with the case.)
    – user
    Jun 10 '16 at 21:25

If you have a voltmeter, it may be helpful to check the voltage across the fan when it is running fine (5v or 12v) and when it's making noise.

If the voltage drop is significant, it could be the stator coils shorting, causing desync. This could eventually result in a dead-short failure, possibly damaging the motherboard, or depending on the power supply, causing a hard shutdown (most power supplies have current limiters that shut them off).

If the voltage doesn't drop, it's probably just the hall sensor or something inside the fan controller gone bad/ loose. This will just cause the fan to desync. If you stop it with your hand and give it a push it might recover. This is probably the most likely case and is also (relatively) safe to leave running.

If you have an oscilloscope - and the fan is controlled via a PWM line - check what's going on there, it could be the motherboard/ a loose connection (check it at the fan side - it may be hard to get a probe in there). This is less likely the case.


Other than it being extremely annoying, you won't damage anything in your computer.

If the temp threshold is exceeded, your computer will slow the processor and eventually shut down the computer to avoid damage.

If you put an small portable fan to blow air into your case, you should be fine. I have done this in emergency situations when a fan died on a rack server and I was able to keep it running with no damage or performance loss.

  • This isn't the CPU fan; the CPU has plenty of (forced air and convective) cooling even without the problematic fan. Also, I'm not so much asking about the effects of less cooling as about the possible electrical effects of a fan failure.
    – user
    Jun 10 '16 at 21:03

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