The fan on my old trusty macbook pro started to behave very strangely. It starts then stops then starts then stops and it just continues to happen. CPU gets pretty hot without any load (30-40%) - 72°C as well as laptop. Apparently it is not cooled down properly. When I run something with heavy load it seems to increase RPM but then CPU cools down and I get the issue back.

Potentially relevant infor: I have rather recently ~1 month ago changed battery because the old one became swollen. Obviously I have bought third party battery. Quite some time ago I have replaced RAM (to 16GB) and HDD (to SSD).

What I have tried so far and it didn't help:

  • I have tried to reset SMC twice
  • I have checked that it is not dusty inside and cleaned it to the best of my ability without compressed air and other instruments

I run 10.12.6 with the most recent updates, I didn't seem to install any apps before the issue started to happen.

I have just installed smcFanControll 2.6 and tried to set min fan speed to ~3500 RPM but issue continued. After I have set it to max 6200 RPM the fan tried to do the same but then somehow stabilized and is now spinning constantly at 6200 RPM. This has cooled down CPU and mac in general but obviously it is annoyingly loud.

Any ideas what could have happened?

  • Pure guess - a temperature sensor has either failed or has come adrift. Maybe try iStatMenus (free trial period, $12) to check the individual sensor temps.
    – Tetsujin
    Mar 17, 2018 at 16:44
  • It is not clear from your question if you have verified that it isn't due to a background process that might be using excessive CPU. If you open the Activity Monitor application, and select the CPU tab, and then sort by %CPU (To bring the highest usage items to the top) is there anything that is using more than, say, 10% when the computer is idle? You mentioned 30-40%. Is that the idle load? If so, that is pretty high. Typically, in the activity window, an idle computer should show 96% or better next to "Idle:" at the bottom.
    – J Wolf
    Mar 18, 2018 at 16:54
  • @JWolf well, 30-40% is my "normal" idle. Yes, I have checked that I don't have strange/stray processes. Thanks for suggestion though. Mar 18, 2018 at 19:42
  • @Tetsujin I have smcFanControll and iFanny and both show normal temperatures. I can't see any drift in temperatures. Mar 18, 2018 at 19:43
  • 1
    @Tetsujin Thanks for suggestions. I have bought new fan which has fixed the problem. Mar 22, 2018 at 20:02

1 Answer 1


In all likely hood,your fan has failed and it needs to be replaced.

The stopping and starting is indicative of a bad or seized motor.

  • Probably it is the case. I guess it makes sense that only higher voltage (if I remember my electrotech correctly) manages to spin the fan. I will try to buy a new one next week, replace the old one and report back :) Mar 18, 2018 at 19:45
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    Finally got new fan, installed. Now works as expected. Thanks! Mar 22, 2018 at 20:01

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