Voluntary put the iMac fans to full blast to clean the iMac heat sinks?

rin67630 · Mar 12, 2023

One reads a lot about people complaining about their fanns running full blast.
I have an iMac late 2013 that is used moderately and never had its fans needing to spin full speed.
Today I started with a new install and upon restarting the fans ran for 3 seconds full blast.
A cloud of dust came from the orifice behind the holding foot.

I can imagine that it would be advisable to "clean" the heat sinks from time to tome by a full blast of a minute.

How can one voluntary trigger that blast ? (beside using a dedicated fan-control software).
Someone told that holding the power button for very long would bring the fants to full speed, but I could not get it to work here.

chrfr · Mar 12, 2023

rin67630 said:
One reads a lot about people complaining about their fanns running full blast.
I have an iMac late 2013 that is used moderately and never had its fans needing to spin full speed.
Today I started with a new install and upon restarting the fans ran for 3 seconds full blast.
A cloud of dust came from the orifice behind the holding foot.

I can imagine that it would be advisable to "clean" the heat sinks from time to tome by a full blast of a minute.

How can one voluntary trigger that blast ? (beside using a dedicated fan-control software).
Someone told that holding the power button for very long would bring the fants to full speed, but I could not get it to work here.

This won't clean anything off. The computer would need to run the fans at very high speed in the opposite direction to remove any dust, and that's not what it's doing. Sometimes on startup the computer might have a kernel panic, which will sometimes cause the fans to briefly run at full speed.

rin67630 · Mar 12, 2023

chrfr said:
This won't clean anything off. The computer would need to run the fans at very high speed in the opposite direction to remove any dust, and that's not what it's doing. Sometimes on startup the computer might have a kernel panic, which will sometimes cause the fans to briefly run at full speed.

Indeed it ejected during the 3 seconds of the blow a considerable quantity of dust already. I can imagine more would come out if the blow would last a bit longer.

Here is the picture of the mac's foot and surrounding after the 2-3 sec blow (before it was perfectly clean).

Screenshot

Captured with Lightshot

prnt.sc

It was not dust firmly stuck on the heat sinks -that would require a blow in the opposite direction- but the lose dust that accumulated due to the the very long time running at fan-idle.

wilberforce · Mar 12, 2023

Macs Fan Control app:

Screen Shot 2023-03-12 at 12.25.27 PM.png

I suggest instead vacuum along the bottom vents with the computer off, using some commonsense in how you do it. I do this from time to time to remove dust that builds up on the intake screens.

rin67630 · Mar 13, 2023

wilberforce said:
Macs Fan Control app:

View attachment 2172531

I suggest instead vacuum along the bottom vents with the computer off, using some commonsense in how you do it. I do this from time to time to remove dust that builds up on the intake screens.

The Macs Fan Control app seems to put the fans at 2800 RPM max, which you will barely notice.
The full blast I had by serendipity once at startup was clearly louder.
I would like to be able to reproduce it.

Vacuuming along the bottom vents will not be any efficient at all: look at the cooling construction pictures at iFixit !

There is a single fan taking its inlet from the upper inside of the case and blowing down through a funnel + heat pipe of the logic board to the outlet behind the foot.

wilberforce · Mar 13, 2023

rin67630 said:
The Macs Fan Control app seems to put the fans at 2800 RPM max, which you will barely notice.
The full blast I had by serendipity once at startup was clearly louder.
I would like to be able to reproduce it.

Vacuuming along the bottom vents will not be any efficient at all: look at the cooling construction pictures at iFixit !

There is a single fan taking its inlet from the upper inside of the case and blowing down through a funnel + heat pipe of the logic board to the outlet behind the foot.

Sure, I am fully aware of how the cooling system works, and agree it is not efficient, but short of opening up the iMac, vacuuming the bottom vents is about all I have heard one can do, and it has helped a bit for me and others.
I have not heard of anyone being able to force the fan to run above maximum speed, although I have heard of some cases where a temperature sensor/controller has failed with fans apparently running uncontrollably at greater than their supposed limit, like this:

https://forums.macrumors.com/threads/imac-fans-at-high-speed-all-times.2093543/