iMac heating problems and the curse of the Canon printer driver

Apple's forum has a not-yet-deleted thread on heat concerns with the iMac (ambient light sensor Rev B) model.

Some excerpts:

Apple - Discussions - OVERHEATING (of new iMac & version-B)

... fans started revving higher over the last couple of weeks. Didn't change after I installed 10.4.3. I reset the smu, no change. Then i remembered some one mentioning a dust factor in the bottom vent. So I took off the back and looked. No blistering (actually I've only heard of one case of als blistering yet many seem to have this belief that the rev b hardrives blister from excessive heat.), no capacitors messed up and clean as a whistle. However when I took some air to the vent there was quite a bit of dust in the vent. I made sure all of it was out and the inside were clean, closed it up, reset the smu again and for the last week its been even quieter than when new. temps are normal, except the harddrive is cooler and the fans have been great. If they do start to get louder do to a load, they come back down very quickly after. In short, its behaving better than when I got it.

... I've had more fan noise in the past few weeks. (machine specs as in footer, 3-4 month old ALS G5 2GHz 400MB 1.5GB RAM 20")

I can't tell why, but I think the system runs hotter. I had upgraded from 512 to 1.5GB and I wonder if that's tipped something to a higher temp. I switched to 10.4.3 and did some system maintenance (reset the SMU

Using ThermographX I find:

- low speed mode: CPU 145 F, drive 114 F
- high speed mode: CPU 192 F, drive 126 F with a noticeable persistent fan hum
- automatic: behaves like high speed mode, for some reason I don't seem to stay at the low speed temp once I go to automatic

By your note my system is running consistently ABOVE the "critical point" for the CPU (187F) you referred to.

... AppleCare is not a panacea however. My impression from Macintouch reading is that Apple outsources AppleCare and that the 'repairs' can be questionable. If time is an issue one may be better off going with the extended warrantees that are available with some credit cards and using them to pay for repairs done by a non-Apple authorized service center -- if you can find one! We do have one such in the twin cities.

In the meantime I think persons who bought a Rev B thinking Apple had fixed the design problems with the Rev A need to assume that the Rev B is similarly flawed. Clean the air filters, monitor temperature (themographX is $7), set the machine to sleep when not in use, don't use it as a media server, set the CPU to lower speed.

Update 11/7: This was solved.

When I set Activity Monitor to show ALL processes, not just my processes, I discovered that PrintJobMgr was occupying 90% of my CPU. A google search revealed this is a known problem; a stuck Print Job can drive CPU utilization up, shift the iMac to highest CPU setting, and drive system heat up. The print job was stuck because my Canon IP 4000 ink jet has been flaky ever since I attached it to my Airport Extreme USB print server. I don't like print servers! In this case my wife initiated the print job and I had no idea it never completed. I've also read a comment from an expert source that Canon printer drivers in OS X seem to be very CPU intensive and can cause heat spikes.

The CPU is now running abou 100-110 F and the hard drive about 100-110 F.

In Print Center I found the stuck print job and removed it. The machine started to cool down almost instantly. In automatic mode again the temperature continued to drop, as tracked by 'Hardware Monitor' (which I will buy).

When I figured this out I felt a bit guilty about lambasting Apple for their iMac Rev B persistent heat problems. After further consideration, however, I think a bit of basting is in order (I'll take my lumps too.) There's something wrong when an errant print job can cook a $2000 computer. Four things in particular:

• Why did this job hang in the first place? Why is printing to Apple's Airport Extreme print server unreliable with the Canon IP4000? How much of this is Canon's fault vs. Apple's fault?
  
• Why does PrintMgr hog so much of the CPU?
• Why didn't some process notify the user of a rogue job?
• Lastly, of course, this does emphasize that the iMac G5 remains vulnerable to overheating with CPU intensive processes.

So Apple does have something to answer for.

BTW, this issue of heat and computation, and monitoring systems for thermal burden, isn't going away. Heat production and power consumption are the key drivers now of system and CPU design -- and this will be so until we cook the planet. (The physical limits of computation are, I dimly recall, somehow related to the ability to dump heat ...)

Update 11/8: A few odd thoughts and tips related to managing heat output on all iMacs

• via Macintouch: turn down LCD brightness
  "The LCD brightness setting has a significant effect on power consumption: minimum 82 W; midpoint 88 W; maximum 106 W. With this in mind, I've set the brightness to minimum, which is perfectly adequate (the factory setting is maximum). This should reduce component thermal stress issues and extend display life, because much of that power is being dissipated as heat, rather than going into actual light output."
• have machine sleep often and rest hard drive aggressively
• this is not a great machine to use as a video server!
• run at temperature monitor and activity monitor routinely -- look for spikes and rogue processes (caveat: I'm seeing some odd system instability doing this, I need to investigate further.)

And a thought on fan noise:

• If the fans are loud -- ask is the system hot (appropriate fan activity) or not (OS bug). Just put your hand in the exhaust stream and feel if it's hot.
• If the system is cool, reset the system management unit (SMU) or even zap pram or reset the open firmware, repair permissions, do a safe start, sacrifice a chicken beneath the full moon, etc.
• If the air exhaust is hot, find out why. Check active processes. Clean the intake vents. Consider the preceding voodoo -- but it likely won't help. Don't let the system run hot -- this is bad.