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 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.

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