Replacing Fans

[amigadave]

This is not exactly Amiga Hardware related, but the answers could be universal to all platforms, so I put the questions here.

I am in the process of replacing computer case fans to reduce noise and need advice from all the big brains here on A.org.

The computer in question is the well know Noise Machine called the G4 PowerMac MDD model.  It has 4 fans inside of it, one 120mmx38mm fan pointed at the dual cpu heatsink, one 60mmx15mm case fan, and two 60mmx25mm PSU fans.

I am not sure which fans are responsible for all the noise, so I am planning on just replacing all four of them with the quietest fans I can find that will provide the same, or better airflow to keep my G4 PowerMac nice and cool inside.  The stock fans do not have air flow numbers on their labels, or even rpm numbers to indicate how much air they are moving and what fans I need to use to replace them with, so I am open to suggestions that are better than just replacing them with the same size and voltage fans and hoping for the best.  All of the fans are only two wire fans, so if they are controlled by the amount of heat sensed by some kind of sensors inside the computer, the motherboard and PSU must be doing all of the fan speed adjustments through only those two wires to the original fans.

Anyone here done this modification or fan replacement before that can offer any advice?

[Kronos]

Not sure bout the MDD, but all orginal fans in my QSs had a small temp-sensitive resistor mounted directly at the fan.

My advice (as little helpfull it may seem):
-get yourself some electronic fan-control preferably with temp-displays
-mount the the temp sensors with the old fans, see how hot it get where
-replace fans with ones that have average or above airflow
-regulate them down to the point where temps are as good as before

And for finding out where the noise comes from:
Stick a screwdriver in each fan after another and listen to the difference (just not for long...)

[amigadave]

Not sure bout the MDD, but all orginal fans in my QSs had a small temp-sensitive resistor mounted directly at the fan.

My advice (as little helpfull it may seem):
-get yourself some electronic fan-control preferably with temp-displays
-mount the the temp sensors with the old fans, see how hot it get where
-replace fans with ones that have average or above airflow
-regulate them down to the point where temps are as good as before

And for finding out where the noise comes from:
Stick a screwdriver in each fan after another and listen to the difference (just not for long...)

Thanks for the advice.  I have tested each fan outside of the case and PSU and the 3 smaller fans are very quiet.  It is the 120mmx120mmx38mm fan next to the dual G4 heat sink that runs at such a high rpm and makes all the noise.

I guess I could buy a fan rpm controller and temperature sensor (actually already have one that would work well at telling me the temp near the heat sink) and try slowing down the fan to make it quieter, while still providing enough air flow to keep the G4's within recommended temperature limits.

I have a MacOSX widget that shows stats on temperatures inside your Mac, but don't know how accurate it is, or if it is compatible with the older G4 PowerMacs.  I use it on my G4 PowerBook and Dual G5 PowerMac and it gives me readings for temperatures and fan rpm's as well as cpu usage.

[Kronos]

.  It is the 120mmx120mmx38mm fan next to the dual G4 heat sink that runs at such a high rpm and makes all the noise.

Good chance that someone allready replaced that ...

The loudest one in my QS was the one behind the CPU-module. 3rd party replacement without that simple temp-sensor....

[Duce]

120mm fans are cheap.

[orange]

120mm fans are cheap.

usually bigger fans make less noise. I'd try some fine oil as lubricant first.
some recommend white lithium grease.

[Iggy]

Yes, usually 120mm fans are quite quite.
But if you feel the need to replace it, they are quite common.