Maximum fan rpm goes from 2700 to 3600?!?

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Maximum fan rpm goes from 2700 to 3600?!?

iMac fan exceeded maximum 2700rpm

Hi, I have an iMac 5K 2017 For about 2.5 years now. I have installed on it both Windows 10 with bootcamp and macOS Catalina.

All those years I have installed Macs Fan Control both on windows and macOS to start the fan earlier than apple’s default cooling plan to help the CPU cool down more effectively.

Always, macs fan control said the maximum limit is 2700rpm for the fan of this iMac and I was fine with that, but today something very strange happens:

I was on windows and started a game. The game freezes for a couple of seconds and windows restarted. Hmm, a normal crash I thought, it happens rarely so I don’t mind it, but after the restart, the fan was making very loud noise!!

I opened macs fan control and at the maximum rpm was reported 3600rpm instead of the normal 2700, and the fan was running at that maximum 3600rpm!! I thought the fan would be damaged so I immediately shut down windows and restarted to macOS, where the fan was running again at those extreme 3600rpm!!

I immediately reseted the SMC controller by disconnecting the iMac’s power cable for 15” and then it returned back to normal with the maximum speed of the fan to 2700rpm.

Does anyone knows what just happened there?? How does the iMac exceeded the hardware limit of 2700rpm to 3600rpm???

And was it possible for the fan to be damaged if I had let it run for more time??

iMac 27" 5K, macOS 10.15

Posted on Mar 19, 2020 8:20 PM

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Answer 1

BDAqua

Level 10

250,253 points

Mar 19, 2020 9:05 PM in response to Simos805

What temps is MFC reporting?

Have you blown the dust out lately?

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Answer 2

Simos805 Author

Level 1

78 points

Mar 20, 2020 2:30 AM in response to BDAqua

Now it reports normal temps. I don’t remember what temps it reported when it reached 3600rpm because my attention was at the fan speed.

Yes I had little thermal problems with the games the last week so I blow the dust from the bottom vents. The air alone removed a lot of dust and then I removed more with a tongs.

Now the vents are looking clean inside (before they was covered with dust), the temps are way better and I don’t experience thermal throttling.

Does that removal pf the dust relates to the extreme fan speeds with the fan exceeding the normal maximum rpm??

(The problem with the fan occurred after I removed the dust from the vents)

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Answer 3

BDAqua

Level 10

250,253 points

Mar 20, 2020 12:00 PM in response to Simos805

Yes, likely associated with knocking the dust loose, possibly with the vents cleared it blew chunks of dust higher up in the insides.

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Answer 4

Simos805 Author

Level 1

78 points

Mar 20, 2020 1:05 PM in response to HWTech

Apple diagnostics didn’t find any hardware problem.

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Answer 5

Simos805 Author

Level 1

78 points

Mar 26, 2020 4:44 AM in response to Simos805

And it happened again yesterday on windows... weird 😕

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Answer 6

HWTech

Level 9

68,606 points

Mar 20, 2020 10:42 AM in response to Simos805

It is very hard to clean the dust from the fan cooling the CPU/GPU heatsink without actually opening the computer. I've seen the heatsinks on some iMacs collect so much dust that you won't be able to remove it by back flushing it through the rear vent opening.

I know when I run a system stress test that the fans don't sound as loud as when a sensor goes bad and the fans run at high speed to protect the system. I think the protective mode runs the fans at a higher rate than macOS.

Since the fans are running normally after the SMC reset, it means the SMC was corrupted or got into a weird state. Try running the Apple Diagnostics to check the cooling system.

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Maximum fan rpm goes from 2700 to 3600?!?

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