My iMac 2009 21.5" is not silent, how can I make the fans quieter, see pics:

[2aw]

My iMac has 2 fans, the CPU fan and the GPU fan, we are going to focus on the CPU fan, as the process is the same for the GPU fan.

The CPU blower fan is at the lower left, it has a 4 pin connecter:

What are my options to quiet down that fan?
I am already using fan control software to set it permanently at 1200 rpm, but that is still not quiet enough for my liking.

I see the fan plug is a standard 4 pin connector.
Can I solder a resistor to it to slow down the fan speed?
If yes, how do I determine what resistor to use? (I am not familiar with soldering and modding electronics)
And the 4 wires are all black, how do I figure out which is the 12 V and 5 V and the 2 ground lines?

In the past, for my desktop tower computer, for a loud fan I used to ground the black wire to the 5 V line, that would make the fan run at 7 V, but this iMac blower fan uses a different plug than the molex connecter. Would there still be a way to attach the ground line to the 5 V and make my fan run at 7 V, that would be a simple solution if it can be done too.

 

[rpmurray]

You could just remove the fan entirely, so it wouldn't make any noise at all. 🤣

Aren't you afraid you'll toast the CPU by doing this? I mean, the fan is there for a reason, and the slower it is the less cooling you get.

 

[2aw]

You could just remove the fan entirely, so it wouldn't make any noise at all. 🤣

Aren't you afraid you'll toast the CPU by doing this? I mean, the fan is there for a reason, and the slower it is the less cooling you get.

I don't mind a higher CPU temperature if it means a more quieter computer.

The CPU temp readout in the first screenshot shows the CPU at 35 C when idle, I read that CPUs can reach up to 90 C during load and still be functional, so the heat is not the problem in this iMac. And even if it was I can always replace the 14 year old thermal paste on the CPU, that is an easy to way to get the current temperature down even more if it has to come to that.

 

[Nguyen Duc Hieu]

Technically, there are several things you can do to keep the fan quieter, while still maintaining low temperature of the iMac.

1. Clean-up the internal of your iMac, especially the fins of the CPU heatsink and the heatsink attached to several parts on the PSU. The PSU of these old iMacs is quite hot. Replace some of those components (transistor, mostly) if possible.

2. Clean-up and grease up the fan => less noise.

3. Replace the thermal paste INSIDE the CPU. You will need to delid it first, google for a guide of CPU deliding process.

4. Lower the ambient temperature (set your A/C to 16 degrees, perhaps)

5. Finally, use Mac Fan Control as you have been using it to reduce the RPM of the fan.

6. If all of the above still could not satisfy you, a water-cooling project is recommendable. It would be quite messy, as there would be 2 long tubes connecting your iMac to an external 20L tank, but when doing the water-cooling, you will remove all fans and the pump will be placed outside of your desktop, so you won't here any noise from it.

 

[2aw]

Technically, there are several things you can do to keep the fan quieter, while still maintaining low temperature of the iMac.

1. Clean-up the internal of your iMac, especially the fins of the CPU heatsink and the heatsink attached to several parts on the PSU. The PSU of these old iMacs is quite hot. Replace some of those components (transistor, mostly) if possible.

2. Clean-up and grease up the fan => less noise.

3. Replace the thermal paste INSIDE the CPU. You will need to delid it first, google for a guide of CPU deliding process.

4. Lower the ambient temperature (set your A/C to 16 degrees, perhaps)

5. Finally, use Mac Fan Control as you have been using it to reduce the RPM of the fan.

6. If all of the above still could not satisfy you, a water-cooling project is recommendable. It would be quite messy, as there would be 2 long tubes connecting your iMac to an external 20L tank, but when doing the water-cooling, you will remove all fans and the pump will be placed outside of your desktop, so you won't here any noise from it.

I want to reduce speed of the fan even more, the fan speed is ALREADY at the lowest possible setting, I want to do a hardware mod like how I said in my first post.

 

[colodane]

Your best option is to procure an inexpensive pair of foam earplugs. You should be happy that your 2009 iMac is still running and usable.

 

[MultiFinder17]

I would very much recommend against setting the fan speed any slower than the minimum. The 2009 iMacs don't run terribly cool on their own (I know, I run one on a regular basis still as well) and you risk damage to the components inside by not removing the heat.

So far as reducing noise, one thing you can certainly easily eliminate is the noise from the spinning hard drive by replacing it with an SSD. If you're still on the original hard drive, it's likely getting a tad loud in its old age and replacing it would be cheap, simple, and offer a notable speed boost to the aging machine. I've run one in mine for years now and it's a decent performer.

As far as the fans go, the suggestions that you dismissed earlier of cleaning and lubing the fans are solid. If it still isn't quiet enough for you, you could always replace the fans with new ones from eBay or something.

 

[Nguyen Duc Hieu]

I want to reduce speed of the fan even more, the fan speed is ALREADY at the lowest possible setting, I want to do a hardware mod like how I said in my first post.

I did include the word TECHNICALLY firstly in my post, didn't I?

 

[floral]

4. Lower the ambient temperature (set your A/C to 16 degrees, perhaps)

I'd imagine setting the A/C to 16 degrees would either make it explode or turn the room into iMac On Ice (guest starring 2aw).

 

[CooperBox]

I want to reduce speed of the fan even more, the fan speed is ALREADY at the lowest possible setting, I want to do a hardware mod like how I said in my first post.

Good to see you've modified your post.

 

[Nguyen Duc Hieu]

I'd imagine setting the A/C to 16 degrees would either make it explode or turn the room into iMac On Ice (guest starring 2aw).

I meant Celcius...

 

[floral]

I meant Celcius...

Ohhh. Sorry. How much is that in Fahrenheit?

 

[CooperBox]

Ohhh. Sorry. How much is that in Fahrenheit?

Approx 3 imperial gallons.......
But seriously, 16C = 60.8F

 

[retta283]

Pushing a 14 year old computer in this manner is not recommended. It's only justified to slow fans if you're attempting to preserve the bearings and fan hardware itself, which is largely unnecessary and definitely secondary to preserving the hardware. Once you begin to run past a certain temperature (60c-70c I believe, higher than the readings you're getting but you may well reach this with a decrease in RPM) you are killing the hardware whether you like it or not. Just because you can go up to 90C doesn't mean you want to be there, that's the point when it shuts itself off as a method of self-preservation.

You need to implement the previously mentioned upgrades if you want to get the noise down. Work on the PSU and definitely drop an SSD into it. Remove the optical drive if you like. The HDD is probably the majority of what you're hearing anyway. These will definitely help but you will never make this machine silent.

 

[CooperBox]

Approx 3 imperial gallons.......
But seriously, 16C = 60.8F

It's always intrigued me why the U.S. has steadfastly continued with the Farenheit system which I believe is one of only 3 remaining countries that have not gone metric. It's so straight forward; in centigrade feezing point =0deg C and boiling point 100deg C compared to 32degF and 212degF respectively. Even the Brits started thinking about the change to metric units in the early 70's, especially saying good riddance to their crazy monetery system with 12 pence in a shilling, and 20 shillings in the pound sterling, therefore 240 pence in a pound. Mind blowing!

 

[B S Magnet]

Ohhh. Sorry. How much is that in Fahrenheit?

61°F[reedom].

 

[Amethyst1]

61°F[reedom].

289.15K[ool].

 

[floral]

Approx 3 imperial gallons.......
But seriously, 16C = 60.8F

Ooohh. Cool.

(just be glad I don't use Ks.)

 

[2aw]

Pushing a 14 year old computer in this manner is not recommended. It's only justified to slow fans if you're attempting to preserve the bearings and fan hardware itself, which is largely unnecessary and definitely secondary to preserving the hardware. Once you begin to run past a certain temperature (60c-70c I believe, higher than the readings you're getting but you may well reach this with a decrease in RPM) you are killing the hardware whether you like it or not. Just because you can go up to 90C doesn't mean you want to be there, that's the point when it shuts itself off as a method of self-preservation.

You need to implement the previously mentioned upgrades if you want to get the noise down. Work on the PSU and definitely drop an SSD into it. Remove the optical drive if you like. The HDD is probably the majority of what you're hearing anyway. These will definitely help but you will never make this machine silent.

I didn't mention in the OP that I already swapped the HDD with an SSD a long time ago, and unplugged the HDD fan (which was the loudest fan).
I already removed the ODD a long time ago too since it was defective.

I already retired this 21.5" iMac, because I realize now that all iMacs are loud machines, unless there is a way to reduce the fan voltage of the 2 remaining blower fans, all future iMacs are unbuyable for me because they will never as silent as my 15" MacBook Pro.

 

[Amethyst1]

[…] I realize now that all iMacs are loud machines […]

How can you generalise from one model to all of them? I have yet to hear the fan of my iMac. And I’m sensitive to fan noise. In other words, I hate it.

 

[2aw]

How can you generalise from one model to all of them? I have yet to hear the fan of my iMac. And I’m sensitive to fan noise. In other words, I hate it.

I dont know much CPU history, but your machine is 6 years newer than my iMac, so maybe there has been thermal improvements from Intel. (But I also read that very last released 2020 27" iMacs are audible even when idle, so that is why I put off buying one forever. They run too hot and that is why Apple left Intel and switched over to ARM CPUs).

At the rate Apple is doing things now (ever since Steve Jobs died Apple has started making loud computers again, what a shame) the only Apple computers I can stand are their laptops (some of the quietest laptops currently on the market) and the Mac Mini (because I can put it on the floor, further from my ears), all the rest of the Apple computer line-up is non-silent at idle.

For all computers that I use, I must not hear the fan noise when idle.
The 2014 15" MacBook Pro passes that test, the 2009 21.5" iMac doesn't (it has a quiet hum from the 2 remaining blower fans at idle, even at their lowest fan speed, very annoying during the day and very very annoying in the evening).

 

[Amethyst1]

I dont know much CPU history, but your machine is 6 years newer than my iMac, so maybe there has been thermal improvements from Intel.

There sure have been. My iMac also lacks a discrete GPU, which means even less heat.

But I also read that very last released 2020 27" iMacs are audible even when idle, so that is why I put off buying one forever.

The 27” iMacs have more powerful CPUs and GPUs so there’s more heat to deal with.

For all computers that I use, I must not hear the fan noise when idle.

My iMac passes this test with flying colours. My point is, your statement “that all iMacs are loud” isn’t accurate at all.

 

[B S Magnet]

I didn't mention in the OP that I already swapped the HDD with an SSD a long time ago, and unplugged the HDD fan (which was the loudest fan).
I already removed the ODD a long time ago too since it was defective.

I already retired this 21.5" iMac, because I realize now that all iMacs are loud machines, unless there is a way to reduce the fan voltage of the 2 remaining blower fans, all future iMacs are unbuyable for me because they will never as silent as my 15" MacBook Pro.

Odd. My 21.5-inch 2013 iMac is set to run the fan at maximum, because I want the internals to be cool. Also, I can actually do this because the fan in my model is stunningly quiet, even at 3200rpm.