Unlike PCs, Macs usually tend to be quite cool. The PowerPC only consumes little power, compared to a Pentium or an Athlon, therefore they also produce little heat. While all modern PC CPUs need active cooling today, namely a fan or even kryo technology, the G3 and G4 CPUs still cool well enough with passive cooling heat sinks. So you might find that cooling your CPU is not really necessary. That is true...unless you have overclocked your CPU. With CPU upgrade cards getting cheaper every other week and being widely available, many users (mainly the hardcore gamers), have overclocked their CPUs to get more performance for less money. A typical overclocking might be from 450 to 500 for example. (this also makes sense, since you can get a 450MHz Zif upgrade for as little as 250$, while 500MHz Zifs usually cost around 500$ or even more. Some CPU upgrades even allow to adjust the settings without voiding the warranty by changing the jumper settings. However, chips tend to run hot when run at speeds they were not designed for. (as an example take my Motorola Aluminium G3 266MHz. Overclocking it to 300MHz increased its temperature by roughly 4°C. While this still is low (32°C total), it still is hotter than it was before. A G3 450Mhz might be as hot as 50°C or even more.
Another, much more serious problem is posed by todays graphics cards. Cards like the Voodoo2 and Voodoo3 get extremely hot. The fact that they can all be easily overclocked makes this problem even more serious. Depending on the case of your Mac and the CPU/graphics card configuration, you might run too hot to run stable for more than a few hours. The most extreme situation you might encounter is having an overclocked G3 450 or a normal G4 450 with a Voodoo3 card and a Voodoo2 or Voodoo1 card in the same system. I have a Beige G3 266av @ 300Mhz with a Voodoo1 card @ 55Mhz and a Voodoo3 card @ 157Mhz. It is quite obvious, that this system runs pretty warm. What aggreviates the situation is that my main fan (the standard built-in fan in the power supply) blows against a wall, not allowing for too much air circulation. I have no other way to position my Mac however. So what is the obvious conclusion? Add cooling, add fans. I'll illustrate how to add cooling in a K1/K2 tower (8600-beige G3), since that is currently the only system I have had the opportunity AND need to add cooling. However, I'll also try to point out a few methods that can also be applied with other cases.
Cool as a cucumber
CPU cooling
There are basically three ways to cool a Mac CPU.
1. Add a bigger heatsink. This may be pretty difficult, since most Macs have custom heat sinks. Still it remains a theoretical solution.
2. Add thermal paste. Smearing some thermal paste/grease between CPU and heatsink highly improves heat flux and can diminish heat build up a lot. And it all doesn't cost much and is easy to do. Just remove the clip that holds the heat sink on the CPU, smear some paste on the back of the heat sink and reattach it. (Use little paste, not the whole tube). Make sure you are grounded properly whenever you fiddle with stuff inside your computer.
3. Add a fan. The last option is to replace the heat sink by a fan or putting a fan on top of the heatsink (common in the PC world). Every Mac has different formats again, so it is hard to tell what kind/size of fan you need. Once the fan is mounted above the CPU, you can get those babies pretty cool though.
Card cooling
There are basically two ways of adding fans to PCI or AGP cards.
1. On card fans. There are coolers especially designed for Voodoo cards. Those coolers are mounted very close to the card. The are fixated with the PCI card retainer screw. They cost around 25$ each. Go to 3dfxcool to get more info on those products.
2. Improving standard cooling. Of course all the tactics that can be applied on CPUs are also valuable on graphic card chips. (namely fans and thermal grease)
3. Adding fans to the case. Some cases feature extra slots for additional fans in the case. The K1/K2 cases are a good example for that. Installation of fans is really simple there. All you need is an appropriate cooler and the appropriate wiring to power them. (Or you can tinker it together too)
Hardcore tinkering
Special cooling
You can skip this part and read the next chapter, but if you are interested in tinkering or if you are looking for more grammar mistakes, please read on. I recently got a few old Macs to tinker with. Among 2 partial Quadra 840av, 2 PowerMacs 8100 and some others, were also 6 Performa 6200. Unfortunately I found that 5 of them didn't work anymore. Upon closer inspection I discovered that these Macs obviously had a very serious fault in case design. The power supply is almost completely cut off any air circulation. Since the power supply is by far the hottest part of those machines, it would need a lot of cooling. Since someone obviously messed with the design, the part remains almost uncooled though. This causes the part to become very hot even in shut down state. (the power supply is always under electricity). The resistors and capacitors on the power supply platine get so extremely hot that the solder starts to melt away, the platine burns out and literally crumbles to ashes. However, I said only 5 were burnt beyond repair. One still works. However I soon realised that the power supply of this last working 6200 would only survive if I could add some cooling and if I would unplug it whenever I would not use it. So I had 5 spare fans out of the broken 6200s and one working 6200 (that would only start up when at room temperature or lower, I guess the metal expanded somehow after a slight temperature rise and disabled some contact.) What else is more obvious than adding an extra fan to the power supply?
I sawed a square hole out off the top case cover, right above the power supply. The diameter has to match the diameter of the fan of course, in my case it was a 8x8cm fan. I attached the wires to the standard fan supply as shown above. Then you have the choice of having it blow into the case or blow out of the case, depending on the mounting direction. I call my system "Monica", that means it sucks the air inside. However, it is usually more intelligent to have fans blow out of a case, because of dust collection. In the 6200 case it is more useful to have it suck though, because the CPU fan blows, causing a nice air circulation. My Mac now looks like a dragster racing car, but at least I can run it without having to worry that the power supply overheats.
Caution!!
Before you do anything with your or someone else's Mac, make sure to read this chapter.
Not all the tricks and suggestions here have been tested by myself. Some of them may damage parts of your computer, even beyond repair. Adding a cooler to a power supply is nothing for fools, remember we have high voltage in there. I can and will NOT take any responsibility for any actions you perform on your computer or parts of it. Any damage you cause is your own fault unless it is the fault of the part's manufacturer, in any case it is not my fault. Well all I can say again and again is:
- Make sure you are grounded properly when fiddling with things inside your Mac.
- Always pull the plug before fiddling with any electronic and electric devices.
- Be careful what you do and be sure you want to do it, some things are irreversible.
- If you have questions about certain tasks, ask some qualified person before doing something silly.
- Additional fans may transform your silent Mac into a bulldozer, noisewise.
- Have fun.
Text: © by Bensch Blaser, Jan. 2000, all trademarks are property of their respective owners.
Pictures: © by Bensch Blaser, Jan. 2000