insane fan speed readings from lm_sensors

[Leon Goldstein]

Hi Lonni:

All I can suggest is run System Monitor to see the CPU % activity when 
the fan speed rises.

Can you hear the difference in fan speed?  I have a laptop that gets 
very conspicuously noisier when CPU capacity is peaking, as e.g. during 
an update kernel installation.  (I'm using Mint 18.3 Mate.)

On 9/11/19 8:39 PM, Lonni J Friedman via Linux-users wrote:
> Since its so quiet here (when is it not?), I'll drop a puzzle on you
> fine folks to noodle on.
>
> I recently started monitoring my system exhaust fan speed (RPMs),
> mostly out of curiosity.  What I discovered has exposed a mystery that
> I'm struggling to explain.  Every day between 04:00 & 10:00, the fan
> speed readings start to rapidly oscillate between sane numbers (under
> 3000 RPM) and insane numbers (over 10,000 RPM).  For the rest of the
> day, the readings are perfectly normal & reasonable.  Its always
> during that same time window.  There's no way this exhaust fan is even
> capable of spinning at the rate that is being reported.  This has to
> be an erroneous reading.
>
> Here's a graph of what I'm talking about:
> https://imgur.com/erXGz4J
>
> There's nothing in dmesg or /var/log/messages to explain this
> behavior.  I've looked at every cronjob running on the system for some
> bizarre correlation, and can't find anything.
>
> I'd like to think that if this was a flaky sensor, it wouldn't be so
> reliable in when it happens.  So something else must explain the
> weirdness.  Anyone have ideas/suggestions?
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-- 
Leon A. Goldstein
System L3
Linux Mint 17.3