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mac57mac57

macrumors regular
Original poster
Aug 2, 2024
232
120
Myrtle Beach, SC
As part of the "Snow Leopard on PPC" threads and related work, I mentioned that I am going to retry the SLPPC install based on the wealth of knowledge to be had in these pages. I also mentioned that I am going to retry it on my G5 Quad, which regrettably is running hot and loud - fans near 3600 rpm all the time. Very noisy to say the least.

I got the Quad out of storage, opened it up and visually ensured that there was no obvious dust, obstructions etc. to the cooling system. I checked the voltage of the battery and it was clean and good. Then I removed the "G5" cover from the CPU area and checked the cooling lines, pumps etc. No signs of any leakage or corrosion, so that is good. I closed it back up, wired it up and turned it on. Even after years of sitting idly in the lab, it fired right up and booted cleanly into Tiger.

The fans, always somewhat noisy at start up on these machines, settled right down and became quiet. Then they quickly started to creep back up again, reaching about 3360 rpm and settling there. The CPU temperature, as reported by MenuMeters, shows a steady 51C to 53C. My G5 DP 2.3 GHz, whose fans idle at about 1100 rpm, idles in the 57C - 58C area, so I am guessing that the Quad can run at its shown CPU temperature of 51C-53C without any damage to the CPUs. The cooling system IS doing its job, it is just darned noisy while doing it.

Just to try the obvious, I restarted the Quad and zapped the PRAM, just in case... but, no change in behavior.

So, thanks to the good denizens of these forums, I believe that my next step is thermal calibration, and to that end I have acquired Apple Service Diagnostics (ASD) 2.6.3 and will give that a go. I will read everything I can on thermal calibration before attempting it. I dimly recall doing such a thing back in 2011 when I first acquired the Quad.

I have read a lot of the threads here at MacRumors on G5 cooling/fans issues, but I have not yet come across any "silver bullets". There may not be any. Like radiators everywhere, perhaps this one is just low on fluid and thus less efficient. I may try some "jury rig" solutions along the way: adding extra fans, etc. to see if it has any impact, but given the position of the CPUs, I doubt that this will have much effect. Thermal calibration first, followed by other steps as the results suggest.

Any and all distilled wisdom on the best way to approach this will be most welcome.

p.s.> While I typed up this post, the fans have crept up to 3600 rpm, their top speed I believe, and CPU temperature has increased to 56C. The machine may not be thermally stable in the long term. I will watch it and see.
 

mac57mac57

macrumors regular
Original poster
Aug 2, 2024
232
120
Myrtle Beach, SC
Well... the thermal paste COULD need replacing, but I can honestly say that in all my years of retro-computing work, I have never seen a replacement of thermal paste resolve an overheating problem. I HAVE seen it lower CPU operating temperatures by a few degrees, but that is about it.

That having been said, it seems inevitable that I will try it at some point; I have fresh, high quality thermal paste on hand; I just redid the paste on a 3 GHz Pentium IV that was overheating. It did lower the CPU temp by 3 degrees or so, but the problem continued. That one turned out to be the power supply; the +12v and -12v lines became flakey once the power supply heated up.

As regards the Quad, my guess is coolant loss, or perhaps breakdown of the thermal properties of the coolant. Either way, I suspect that I will need to recharge the coolant. Time, and experimentation, will tell.
 

topcat001

macrumors 6502
Nov 17, 2019
287
141
Actually, you may be right. Replacing the coolant is probably going to have a bigger effect.
 

mac57mac57

macrumors regular
Original poster
Aug 2, 2024
232
120
Myrtle Beach, SC
A quick update here - on a whim I checked the G5 Quad Energy Saver control panel, the Options tab. Sure enough, the Processor Performance drop down was set to "Highest" (I probably set it that way years ago - I am a bit of a performance freak!). I changed it to "Automatic" and let the machine run. It settled out at around 2800 RPM and about 50 C. It still makes more noise than I find acceptable, but it is cooler and "quieter" already. It was up in the higher 50s and 3600 RPM.

Despite the noise, the CPUs are being kept in an excellent temperature range. Anything in the 50s is great. I did some reading today on the maximum safe operating temperature for the 970MP. It appears that anything less than 85C is quite acceptable, and it can burst up to just over 100C for short periods with no damage.

Meantime, I also did some reading on the process for flushing and replacing the coolant on G5 Quads. It is a daunting process, and apparently the components involved (especially the radiator) are not particularly sturdy - VERY easy to break something as you try to fix something else.

I have a number of large no-noise case cooling fans - I am going to try adding one or two of these to see if I can get extra efficiency out of the radiator. I don't want to engage in something as long and difficult as a coolant swap unless I really have to!
 
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