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Hot CPU? Three Ways to Keep Your Cool

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For a product as cool as the MacBook Pro, it sure does get hot. Too hot, sometimes. I’ve had many laptops in my time, and I’d never go back to plastic IBM compatibles as long as Apple (s aapl) keeps churning out these beautiful aluminum machines. But heat dissipation is a real problem for anyone who makes their MacBook work hard.

It’s important to keep temperatures as low as possible because a hot CPU is a stressed CPU, and if a processor runs too hot for too long, it runs a higher risk of becoming damaged. Until then, a machine that runs too hot is prone to freezing or crashing.

There are two things to keep in mind before we get started. The first is that — for the most part — MacBooks don’t normally “overheat.” Sure, they get hot, but they are designed to get hot. A casual few minutes spent on Google reveals far too many people casually talking about their machines “overheating,” when what they really mean is that their machines are getting “hot.” And by “hot,” we mean “very warm.” But not painfully hot. And certainly not egg-frying hot. If your MacBook truly reaches those temperatures, you should stop using it and take it to your nearest Apple dealer for repair, not complain about it on discussion boards!

The second thing to keep in mind is that a MacBook’s fans have been pre-programmed by Apple. There’s more on this below, but it’s worth remembering that Apple has invested a great deal of time and expense developing today’s MacBook range. If anyone can be considered an expert in MacBook cooling, it’s Apple. So if you are unsure about how to proceed, or don’t feel comfortable modifying your Mac’s settings, then simply skip to the Common Sense Fix below.

I have a three-pronged approach to keeping my MacBook cool. There’s the Hardware Fix, the Software Fix and, overarching both of those, the Common Sense Fix. Let’s start with that one.

The Common Sense Fix

They might be discreetly positioned along the back edge of your machine and hard to spot, but a MacBook does have air vents. The internal fans are trying to push hot air out through those vents. Try not to cover or obstruct them with fabric or, say, thick cables.

The human body, bed covers and clothing — they’re all poor conductors but great insulators. If you rest your MacBook on your bed, lap or stomach for a long while, it’s going to get uncomfortably hot because there’s probably insufficient air-flow around the vents and because the surfaces you’re using can’t efficiently conduct heat away from the machine.

The Hardware Fix

Aside from torsional strength and rigidity, the aluminum unibody of modern MacBooks brings another useful property to the mix; metal is a great conductor of heat. Far better, in fact, than the plastic shells of most laptops. Apple exploits this property by using the entire body of the machine as an efficient means for drawing heat away from the MacBook’s processors. In other words, the entire machine (sans lid) becomes a giant heat sink.

Under minimal processor load, or in Energy Saver profiles, this is usually enough to keep the processor reasonably cool, and the MacBook’s fans will generally stay below a thousand rpm. At that speed, they’re usually near-silent in a quiet room.

But plug your machine in to a power outlet, burn a DVD and do some heavy Photoshop work and things start getting hot. The underside of my MacBook Pro (late 2008 model) can get uncomfortably warm when pushing the processor with these sorts of tasks. The fans will kick in to high gear at this point — spinning at least a few thousand rpm — enough for them to suddenly be quite noticeable.

If you absolutely must continue working, and the Common Sense Fix hasn’t stopped your MacBook from getting itself all hot under the collar, you might want to consider buying an external laptop cooler. There are hundreds of models out there, and they mostly do about as well as one another.

Don’t expect miracles though; a laptop cooler is unlikely to guarantee ice-cold conditions for your precious processors. I’ve been through a few coolers in my time and, other than some extraordinary variances in price, none have ever left a laptop noticeably cold to the touch. Moderately cooler, yes.

The Software Fix

Hardware cooling, because it’s usually pretty moderate, is only part of the solution to getting your MacBook’s temperature under control. Here is where you use the machine’s internal fans to get things really cool.

There are several software solutions for managing your machine’s on-board fans. I use one called smcFanControl, a popular free app that’s very easy to use. smcFanControl provides a constant (and unobtrusive) readout of my MacBook’s core temperature and fan speed. If I notice the machine is getting hot and want to bring it down a few degrees, I can temporarily ramp up the fans.

smcFanControl Menu Bar

This is my personal solution, I’ve found it works well enough for me. What do you do to keep your core cool? Let us know in the comments.

25 Responses to “Hot CPU? Three Ways to Keep Your Cool”

  1. Not to rain on your parade, but if you have a program like smcFanControl installed and need to take your Mac to the Genius bar for some problem – they won’t touch it as you have installed software that mucks with Apple’s carefully thought through and tested plans. It does state this somewhere in the warranty – that you invalidate by installing any software that mucks around with the hardware basically.

    Just for your information anyway…

  2. Anonymous

    Another vote for the CRYO LX cooler because of looks but has sharp edges. When I stress tested them using Temperature Monitor after about 20 minutes between tests I got the following:

    MacBook Pro Unibody 2.53 with 9600M GT with 512MB enabled:
    Idle CPU temp:
    on desk: 66
    on cooler w/ fans off: 66
    cooler fans low: 60
    cooler fans high: 61

    Load CPU temp:
    on desk: 84
    on cooler fans off: 81
    cooler fans low: 82
    cooler fans high: 82

    My conclusion is that the MBP is mainly an air outlet vent with the graphics card enabled and the Cryo LX blows air up and is actually competing with the air outlet of the internal fans. The enclosure is cool but the components aren’t. I opened my Cryo up and switched the stock fans with Noctua NF-P12 ones- looks terrible but you can’t see them with the laptop on it, and it is silent on low. Which got me another degree. Overall hardly worth it for an $70 cooler, look for good reviews of a cooler on a unibody or try to control the direction of the fans to achieve better results.

    Funny that the largest drop was from it just sitting on a cooler with no fans during load (when it matters) seems like most companies know this because there isn’t active cooling on most stands/coolers designed for MBP.

  3. I didn’t have a huge heat problem until I replaced my 5400rpm drive with a 7200rpm drive in my pre-uniBody MacBookPro. Then it only gets too hot generally when I’m at work running Windows in Parallels. I’ve been using smcFanControl and its awesome, as you said :D

  4. The only time I have a problem with excessive heat is when I’m in bed with my MBP and the vents are blocked by my pillows, and when I have a stray process going crazy eating up all my resources. Usually this is a flash or java app on a web page, and occasionally a dashboard widget will just freak out.

    The first thing I do when I hear my fans power up is open activity monitor and check for and kill any runaway processes, once I do the MBP returns to its regular operating temperature in a few minutes.

  5. I already take the care of the ‘Common Sense’ fix and hardware fix you mentioned here, for the software fix, I use iStat Menus, which also like smcFanControl, quietly sits in the menu bar, and offers much more functionality and takes lesser memory.

  6. While encoding movies via Handbrake, with 180% + CPU utilization, the temperatures have reached a maximum of 78 degrees Celsius.

    ??? 180% ???

  7. ljpiii

    I use Coolbook for my Macbook Air and it works very well. Before using the program I was consistently pushing 70-75c with just surfing with Safari. If I tried to watch a movie, or YouTube video, forget about it. The heat would shut down one of the cores and the computer would slow down to a crawl. Additionally the video would become so choppy that it was completely unwatchable.
    After installing Coolbook, my Macbook is like a whole new computer now. I’ve been able to run video while multi-tasking with other programs and It never gets over 85c, and never slows down. It saved me from returning my Air.
    Well worth the $10.

  8. I should add that unlike for some earlier MacBooks, possibly the Core Duo ones, there was a tool available to turn off one of the Cores to decrease power consumption and consequently, heat dissipation.

    CoolBook? Thats not available for newer ‘Books, though I’d want it to.

  9. I would like to assume that the ambient room temperatures have a lot to do with this.

    During moderately heavy tasks, my Oct 2008 Aluminum MacBook 2.0 does get uncomfortable enough to necessitate the use of an external keyboard, because the palm-rests are hot to touch.

    It’s mid-summer here with day temperatures looming around 35 C.

    While encoding movies via Handbrake, with 180% + CPU utilization, the temperatures have reached a maximum of 78 degrees Celsius.

    Should I be concerned?

  10. meumeters and Activity Monitor. Is it getting ho, well the CPU is overloaded, you wouuld see the percentage of the CPU use wit menumeters. IF desired, Activity Monitor is two clicks away from the menu bar: click on the percentage, and check what’ bugging the CPU having all processes visible and sorted by processor usage…
    Wanna check what was hanging? Access Console the same way


  11. My wife and I have the CRYO LX coolers from NZXT and love them. I have 2007 MBP (2.33Ghz) and with Postbox, Safari, iTunes, LimeChat, Adium, Skype, Evernote, Tweetie and a few other menu items up and running I only sit around 55-60C…. Crank up Photoshop or run flash (hulu, netflix) it jumps to the low 70C… I love getting up and seeing it around 43C in the mornings…

  12. WTF!!

    You have a unibody Macbook Pro and can keep it below 1000rpm??

    Mine is set to 200rpm as standard and I use smcFanControl to take it up to 3000 and very rarely 4000rpm.

    The temp. is normally at 50-60°C when having a few applications open, 40° when having none or one and 75° when having a lot big applications open.