iMac G4 fans going non-stop

Most computers run fans at a low speed during idle. I've never owned an iMac G4, but it probably shouldn't be all that loud. How loud is it?

If its just hearing a hum over night when there isn't anything else in the room making noise, its normal. An easy way to get your Mac to let you sleep is to put your mac to sleep-sleep shuts off the fans.

If its sounds like a jet taking off, one of the fans might not be seated properly or off balance. Make sure your Mac is level. If that doesn't help at all it might be a deeper hardware/software problem. You could try reinstalling the OS (10.3 or 10.4?). If you have some cash lying under the bed, you could take it to an Apple store and have it repaired. Noise isn't really a vital system function though, so if you can live with it it might be the best option. My external drive makes this horrible huming/screaming/grinding sound which is quite audible at night, but I find it hard to sleep when I go to a hotel where its dead silent now.

Good luck with your iMac.

It is possible that some dust has snuck inside and is inhibiting air flow between the fan and heatsink causing the processor to run hot and thus the fans speed up in an effort to cool the processor drawing in even more dust which then makes the problem worse? This wouldn't explain the read/lseek though.

the fan on ALL imac g4 models is NEVER supposed to turn off. the other noises are probably the HD which is normal.

theres dust inside... taht was the prob with mine

The fans on the iMac G4 always run. They do not shut off, at all like a Powerbook or iBook. I don't think they speed throttle either. However if they do throttle, it is possible that there is a lot of dust inside the case that is causing them to run faster than usual.

My experience of this is that the cooling of the iMac G4 needs some maintenance with time. This circular dome design has a motherboard at the bottom where a heatpipe arrangement transports heat from the CPU out to the edges of the case. There are two contact surfaces (at least on the late models), one on each end, that when the bottom unit is screwed in place the metal frame inside the dome gets in contact with the heatpipe, thus taking care of cooling the CPU using passive cooling. The cooling is also active in the sense that the fan will measure overall temperature inside the dome and as it rises (as a result of the dome frame somewhat increasing its temperature and from heat dissipated from the hard drive) the fan speed will gradually increase.

The heat conductive paste applied at the heat pipe mating surfaces will dry out over time making the heat transfer less effective. Especially if you open up the case and reassemble things without applying fresh heat transfer paste at the mating surfaces you will break that seal and the dried paste will not make good contact upon reassembly. The result will be that the CPU and heat pipe will heat up a lot without the heat being transferred to the case. The dissipated heat from the pipe will instead flow upwards inside the dome, the fan detects increased temperature and will spin up in an attempt to evacuate the heat. The G4 hairdryer symptom. Eventually the CPU could reaches excessive temperature and will freeze execution or cause an OS crash.
If you´re lucky the CPU and other parts exposed to the heat will survive and the machine will work once it has cooled down. But you won´t get much enjoyment from the G4 with a noisy fan. The solution is to re-do the heat conductive paste treatment. Upon reassembly you will notice that the fan does not rev up as high and it takes much longer for any increase in fan speed since a lot of heat is taken up by the dome frame.

Further silencing

The G4 in stock specs features a 3.5" IDE hard drive and the fan by now has some age so the fan motor bearings could be audible. So in terms of making the machine more silent you could also experiment with replacing the 92mm fan with some recent low noise equivalent. It is possible to get a 3.5" to 2.5" IDE drive adapter so you could run a quieter and cooler 2.5" IDE drive that help keep the fan speed down and overall noise down.

CAUTION: Applying that heat paste can be a real trauma if you get paste onto fingers, and then grab the dome with your hands during reassembly. The matte white plastic easily stains from the grease and will look shabby. You can get into real trouble trying to get that special grease out of the plastic using ordinary soap water or similar. I found mechanic workshop hand washing paste (that type with microscopic plastic particles in it) wss a real blessing for getting that grease removed from a stained dome..

Great info....but you realize this thread is 5 years old - right?

Using this thread to resolve consistent fan noise with my recently acquired iMac G4 1.25 20".

No matter the age of a thread, relevant info is still much appreciated (Q2 2023).

nbrb said:

Using this thread to resolve consistent fan noise with my recently acquired iMac G4 1.25 20".

No matter the age of a thread, relevant info is still much appreciated (Q2 2023).

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You more than likely need to re-apply thermal paste for this machine and give it a good dusting. Clean fan blades as well when you do this. There is no good way to remedy this issue without opening the computer, unfortunately; but once it's done the machine should run very cool and quiet.

someguy said:

Ever since I bought my iMac G4 from another user here at MR, the fans on it have been going non-stop and it's kind of irritating at night when it is the only thing you hear. I have been told by a few people that this isn't normal.

Even when the display is off and the system hasn't been used for hours, the fans huff out air through the top vents. I checked Activity Monitor and CPU usage is normal (below 10%). The air coming out of the base isn't even warm at all. I want this thing to quiet down!

Is there anything I can do?


EDIT: sudo fs_usage shows WindowServer making CACHE_HIT calls or whatever like 40-50 times a second. Is this something that could be a problem? On my PB, there is basically nothing going on when you run that terminal command.

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Did you mean the desk lamp iMac?

This Mac only has one fan inside. This is working all the time and has his own temperature diode. The fan speed is only controlled by the temperature of air that goes through the fan where the diode is.

The only way to make the Mac more silent is to install a more silent fan with PTC diode. These fans are hard to find.

Perhaps this will help a bit: https://forums.macrumors.com/threads/imac-g4-usb2-upgraded-to-ssd-and-2gb-ram.1003716/post-24244588