Solved Random Fan Speed Bursts

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Daimos

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Sep 6, 2019
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I have a new Lenovo Ideapad Laptop since last September. Recently I noticed that my CPU fan speed greatly increases from time to time while CPU load is around 10%. I checked using HWiNFO64 and it shows that my Core 0 heat sensor reports 40C, then suddenly jumps to 75C and then after around 2 seconds jumps to 40C again. It seems that during that heat spike fans respond by going into high gear. Could this be caused by dust or maybe it's a sensor failure?
 

phillpower2

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Sep 9, 2016
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It seems that during that heat spike fans respond by going into high gear.
That is normal fan behaviour, the cooling fan works on a thermal trigger and even when idle the CPU gets warmer the longer that the computer is on.
 

Daimos

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Sep 6, 2019
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Fans should increase their speed gradually, not on a trigger, but using an interpolation: X C heat equals X RPM, X+25% C heat equals X+25% RPM, or something similar. If sensor samples heat 10 times per second, then RPM should also change 10 times per second. This should eliminate those NOISY fan bursts.
 

phillpower2

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We will take your word for that Daimos and thank you for such an easy to understand explanation o_O

Being that the notebook is relatively new and therefore still covered by warranty Lenovo tech support should be your first port of call if you think there is something amiss with the notebook.
 
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Daimos

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It seems I found a solution: disabling Turbo Boost. Now my CPU core 0 is clocked at around 2.3 GHz instead of 3.8 GHz. This limits heat spikes to 48 C instead of 76 C and the fan noise gone.
 

phillpower2

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Glad you got it sorted and thanks for letting us know (y)

Question, was it happening when the system was idle or just under load.
 

Daimos

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It was under light load: 10-20%. The problem were those heat spikes. I also changed CPU cooling policy from active to passive which prefers CPU throttling rather than fan burst.
 
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