PART ONE
Location - location - locations… 
“Bite down.”
Silly me, I thought that a new GPU thermal pad would decrease temperatures - but as Wozniattack reported, temps do rise with a new GPU thermal pad in place. And maybe that is good news for your GPU’s extended lifespan. (This example was tested before install of new thermal pad.)
We’ve all seen those aftermarket upright stands for the G4 minis and even some under tabletop mounts designed to free up available working space? But now, after all of these temperature studies and my own personal view that… G4 mini OS 9 users are now more likely to use them for gaming (and thus increasing & prolonging periods of demand and stress upon the CPU & GPU)… doesn’t increased or more adequate cooling become more of a legitimate concern?
Along the path to determining possible temperature differences between old and new GPU thermal pads… briefly tested standing a mini up on its left side. That places the hottest areas of the mini’s bottom up⬆︎ and off of tabletops and more into cooler, circulating ambient air. (Most internal heat is generated by the CPU and GPU.) *Definitely more effective than my standard bottom application of four, eighth-inch thick feet - one at each corner of the rubber padded bottom - to allow for a slight cooling air gap between the mini’s bottom and tabletop.
Just kept thinking that having a mini resting flat on the bottom rubber pad only contributes to internal heat build up, as heat is then “reflected” up & off of the heated tabletop and sucked back into the mini’s air intake vents by pre-heating some of that intake air, as… it is drawn back into the mini by its little solo cooling fan. (And especially over longer periods of intense & continuous use.)
Thought that Apple might have considered this with the design of their newest minis, but evidently not. They’ve now even eliminated the rear exhaust air vents… and heated exhaust air also exits from the bottom… where cool air is also still drawn in.
(Maybe the newer M4 minis simply don’t get as hot? DieHard, V.Yakob… take some temps will ya?)
Anyway, run any video intensive game or video editing / playback programs and you’ll well-know how a G4 mini’s exhaust air temperature and fan speed rises over elapsed runtimes. (Especially if you’ve never renewed your CPU heatsink’s paste.) Even slightly pre-heated air from a flat tabletop could have a bit of a turbo-effect when it comes to internal heat increase and exhaust temps?
Did not test this approach to any great degree, because also wanted to employ the anemometer to measure differences between the old and new GPU thermal pads - and the anemometer requires a vertical upright orientation… (not possible with the mini on its left side). But did take some temperature readings with an infrared laser thermometer at the three points plotted above on the very top image.
Tested running Cinebench 2003, five times successively for 30 minutes. (Still not the same as running a video game - but ample enough for general test purposes and Cinebench 2003 is easy for everyone to obtain.] Can’t find my notes at present but do remember that the “
CPU center” temperature never rose above 120˚F and that when it did reach that temp (a few times, after only 15 minutes of runtime) it very soon cooled — as evidently the fan speed increased to compensate accordingly. (Yet another side effect of having renewed the CPU’s heatsink paste.)
In addition, also tested using a 4 inch USB powered fan, at a distance of 10-12 inches from the bottom rubber pad, blowing directly at the bottom of the upright mini. Maximum temperatures then never rose above 110˚F after 30 minutes of runtime.
Some possible drawbacks that can be imagined from this “left-side upright” approach, are: (1). possibly knocking it over easily — and (2). possible problems with the CD/DVD drive reading or writing consistently?
So, gamers and/or other video intensive taskmasters… maybe shifting the mini up on its left side could be advantageous when long-running apps or vintage OS 9 games… for keeping the mini cooler? And maybe blowing a bit of additional air from a small fan into your mini, might also just be advantageous in the long run? 10 degrees cooler? *All temps herein are Fahrenheit.
*Never intended to make a career out of this little “mini escapade” but it just made sense to test all of this along the way to
FINALLY gauging any differences from a copper heatsink in a stock mini. All tests here performed on a 1.5 GHz mini with an old 80 GB spinning HD (#5B from this group image:
https://macos9lives.com/smforum/index.php?action=dlattach;topic=7558.0;attach=15284;image
The one interesting stand from CopperDropDesigns can be also be viewed here in more detail:
https://www.instructables.com/Apple-Mac-Mini-Cooler-Made-with-Drawer-Slide-CNC
