The Usefulness Equation

Heat Management for 'Books and the Last Mac to Run OS 9.1

- 2009.01.08 - Tip Jar

MacBook Air Thermal Management with CoolBook

From Jason Wang in response to Software to Keep Your MacBook Cool:

One correction - You can use CoolBook to run at your normal CPU speed with a lower voltage. You said that it simply cuts off the top end of the processor's throttling options, which isn't quite true, although you can do that if you wish.

Lots of first-gen MacBook Air owners (including me) have been using CoolBook to allow our processors to run at 1.6 GHz at reduced voltage. This doesn't affect performance but reduces heat. Stock first-gen MBA's have difficulty running demanding tasks for extended periods of time. For example, many of us were unable to watch a DivX movie from start to finish because the processor would clock itself down from 1.6 to 1.2, causing stuttering. After the CoolBook mod, our computers can now maintain 1.6 GHz at full load indefinitely.

Essentially what I do is reduce stock voltage to 0.9v at 800 and 1200 MHz, and 0.925v at 1400 and 1600 MHz . . . too bad it took a $10 app to fix Apple's big mistake. I also use smcFanControl to keep my fan speed at a minimum 4000 rpm threshold.

-Jason Wang


I realize this about CoolBook. In my article, I was referring to the method that I used to underclock my MacBook. Sorry if that wasn't clear.

I'm glad to hear that CoolBook is helpful to the MBA owners. It's definitely taken the edge off my MacBook's heat. You must remember, the engineers always realize these issues, but whether production continues is an executive decision. I was disappointed to hear the MBAs shipped with such bad thermal management. But there must be a reason for the voltage stepping to be as it is.

I just recently bought a second generation MacBook Pro. When I saw the temperatures go to 90°C at full load, I was afraid there was a cooling system malfunction. I heard people saying that was normal, which was appalling. Needless to say, it's going to get rebuilt to assess that issue. Thermal paste replacement, heatsink shave, the works.

Anyway, If you're MBA is out-of-warranty, you should probably look into replacing your thermal paste. I'm going to cover it soon for a variety of platforms. It should definitely help shave a couple degrees off your average temperature.


Hey Phil,

My girlfriend's roommate has a white MB, and it sounds like a jet engine most of the time. CoolBook + smcFanControl is really a great combo for managing MacBook heat and making them run as they should. 90º really is shocking! I'm not sure what my MBA was doing before, but now it never rises above 80ºC under full sustained load. While still pretty hot, it's well within Intel's tolerances.

I was also disappointed when I called Apple Support after an iTunes video refused to play smoothly. The woman I spoke to plainly told me that it was a known issue with MBA's and that there was no solution. When I contacted iTunes Support for a refund, they did not respond. I definitely did not expect this, since Apple has always been extremely reasonable in the past.

As of now, I won't be rebuilding my MBA since it's under 3 year AppleCare. I'm not really one to tinker with hardware anymore. By the time it dies, I'm sure there will be plenty of good options for replacement.

Good luck with your MacBooks!


Cooling G4 AlBooks

From Roger Pelizzari:

Are the G4 Aluminum PowerBook processors also Ball-Grid Array, or are they pin-based ?

Thanks for a great article.

Roger Pelizzari
Fairfield, Iowa

Hey Roger,

Yes, the G4 AlBooks are BGA as well. For them you can use G4FanControl

Glad you enjoyed the article.


Thanks much. I downloaded it. Do you advise any set threshold?

I have a 1 GHz PowerBook G4.


No problem.

My 12" 1.33 GHz PowerBook is set at 50°C for all three sensors.

The GPU will heat up quickly. Therefore, the fans will come up to full speed almost immediately under high graphics loads. Average temperature for the GPU can be considerably higher than the CPU at any point because of it's design.

Each computer has a specific Idle temperature.

So try this:

  1. Let your PB fully boot into OS X, and open G4FanControl.
  2. Wait 10 minutes for the temperatures to bottom out/reach idle.
  3. Record what those temperatures are:
    • Mine are 50°C Processor / 53°C Northbridge / 55°C Graphics Processor.
    • Since you have the 1 GHz which is the previous generation G4 Chip, it's going to run fairly hotter than my values.
  4. Then slowly turn down the threshold temperature until you hear the fans come up.

I set it 5° higher than that point. Play around and find the point you like it at. If you don't mind the constant fan noise (The 12-inchers fans tend to be quite irritating in my experience) set it lower than the idle temperature.

Good luck!


The Fastest Mac that Can Boot OS 9.1


I was very pleasantly surprised to just discover your articles on Low End Mac - tons of very useful information on the older-Mac world!

I have two very basic questions that I'll bet you know the answers to:

  1. For very specific software reasons, I want to get a "new" older Mac that will run OS 9.1 (versus 9.2). What is the latest Mac that can still run 9.1? (I've assumed that the dual-boot Macs can not handle a clean install of 9.1 - is that true?)
  2. Also, I have an early 2 GHz G5 Mac, purchased 11/03, that has always been as loud as a vacuum cleaner! Do you know of any reasonable fixes for the noise problem on that machine.

Thanks very much for any help you can give - and happy new year!

Al Shultz
San Jose, CA


It looks like you're searching for a Power Mac G4 "Digital Audio". It will run standalone 9.1 - or can dual-boot OS X and OS 9.1.

If you can find an older G4 model, it'll work fine as well. Any standard dual-booting machine released after this one will definitely not run 9.1.

I'd highly recommend trying to find a dual-processor model of one of these, since they're relatively cheap these days and will give you unmatched performance over the single processor machines with OS X. (Even the ones with higher clock speed.)

It's likely that your Mac's thermal paste has completely worn out. The process is a little bit involved, but I'd highly recommend cleaning the heatsinks and replacing the thermal paste with Arctic Silver 5 ($3.97 plus shipping from Cyberguys!). A de-dusting is probably in order as well. I can give you a 95% guarantee it'll be even quieter than when you bought it.

Another piggyback to that solution would be to replace the pass-through cooling fans with quieter ones. They tend to be the main point of noise for the G5 Towers.

I'm going to do a couple feature articles on thermal paste reapplication for at least three models. I'd be happy to throw a G5 onto the list.

Let me know.

Happy new year to you too!

Phil Herlihy


You're a gold mine of helpful information! Thanks so much!

Best regards,

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