View Full Version : PowerMac G5 fan speeds

22nd April 2010, 10:21 PM
Hi MacTalkers,

I picked up a G5 PowerMac (2.7GHz Dual Core) last night for a good price, so I took it home, plugged her in, installed 10.5.8 and started migrating my stuff, but I've noticed every now and again, the fans will spin up, get to the speed they want, then go back to being completely quiet again.

It's quite annoying, and seems to be pretty random. The only thing I can work out is it's when I'm copying files, or doing something else HDD intensive.

Anyone got any ideas on why it's doing it, or if I can even control the fans via an app?


22nd April 2010, 10:48 PM
I had the same problem with my G5 Powermac (2GHx DC) a while back.

Does yours work like a jet engine and the only way to stop is reboot?

In my case, the problem was the ram. I had added 5x2GB kingston rams so upgraded the total memory to 14GB ram and this problem started to occur after that, seemingly in random.

I've tested all the rams on a friends linux box and two of the ram sticks identified as faulty, one was the one I had purchased. I replaced that one and removed the other apple branded ram... it's been over a year now and no more problems with the fan!

22nd April 2010, 10:53 PM
I've got 8x512mb sticks.
It's quiet when you're doing nothing intensive, but when you start copying files and loading large graphics, the fans start spinning up and then stop again when you're done. It's bizarre.

23rd April 2010, 12:01 AM
Your new baby is a liquid-cooled PowerMac ... and therein lies the problem. Apple's experiments in liquid cooling turned out to be a major disaster for the company, as the self contained cooling blocks with their integral radiator and pump were a sealed unit with several flaws -- there are many many horror stories on the web (including one from our very own MacDave) who had a seal rupture and spray the conductive glycol mix all over the CPU board and powersupply, irrevocably destroying the machine.

All PowerMac G5's and iMac G5's are known for 'racing' the fans whenever you try to do something, but unless you are doing something both sustained and heavily-computational, the increase in fan speed should never be drastic. The only time you should hear the fans at full speed is when there's been a kernel panic -- like all G5 Macs and all Intel Macs since, the OS takes full control over the fans throughout the machine, and if the machine crashes bad enough to KP, then the only smarts the fans have is to go to full speed when they stop receiving a control signal.

The symptoms you describe is a tell-tale sign that the coolant system has sprung a minor but permanent leak somewhere and has managed to get itself dangerously low on fluid. Shut the machine down, open the machine's side door, remove the transparent wind panel, and check the absorbent felt pad that should be on the bottom shelf directly above the power supply. This pad should be perfectly clean, and either a bright white or a very faint blue. If there is any sign of a brown stain, you've got, as Lt. Cmdr. Geordie LaForge would say, a coolant leak and things are about to go critical. If the pad is missing, then a previous owner has quite likely removed it, as it was a standard addition to the 2.7's after the problem of a likely leak became known to Apple.

Also use a bright torch to investigate the body of the Mac along the rear, and also check the motherboard underneath the CPU block for any other tell-tale greenish or brownish residue -- all you should see is dust.

A coolant leak in these superceded models is an expensive repair, and you would have to import a refurbished, self contained coolant block from the United States (Apple ran out of them as a new spare part years ago).

23rd April 2010, 06:15 AM
Thanks for the in-depth reply, Brains. I cringed throughout thinking "this is going to be expensive.. this is going to be expensive"

I've already inspected the case pretty well - didn't see any residue, only a couple of dings on the casing itself.
I'll pull the machine apart this afternoon when I get home from work.

23rd April 2010, 12:15 PM
If you can pop the covers off the CPUs to expose the cooling-blocks, check there as well.

Another possibility, if the cooling-blocks seem to pass muster, is that the thermal transfer pads between the CPU and the actual heatsink has degraded -- they all do that over time -- and getting to the CPUs directly, cleaning off the factory-standard residue, smearing on some decent thermal compound and reassembling, might stop the fan racing from being so abrupt.