Is your Mac running hot with Lion? Here’s why.;

After upgrading to Lion (s aapl) on my early 2008 15″ MacBook Pro, I started to notice that the computer was hot to the touch. Really hot. So I started measuring the internal temperature of my Macs to see if there was anything to be truly alarmed about.

It turns out that Mac Intel (s intc) chips have a built-in feature called THERMTRIP that will temporarily suspend the CPU when things get hot, and shut down the CPU altogether when things get too hot. Speculation is that this temperature is somewhere in the neighborhood of 120-130ºC. While my Macs did not reach three digit temperatures, the increase did alarm me. Luckily, as you can see, the temperatures settled down to a normal range after a few days. This is likely due to the machines running a lot of initial tasks like Spotlight indexing of your entire drive just after the Lion upgrade.

Still, if you, like me, are concerned and want to do something a little more proactive than just waiting, here are a few precautionary measures you can take:

iStat Pro Dashboard Widget. One of the first (and lately the only dashboard widgets) I installed is iSlayer’s iStat Pro. This widget will allow you to monitor several of your Mac’s vital statistics, and with the optional companion iOS app, you can monitor your Mac from your iPhone when you’re attached to the same Wi-Fi network. Information reported includes systems various temperatures, and the speed of your Mac’s internal fans. The problem is that as your Mac keeps getting hotter, your fans aren’t spinning faster, something for which we turn to the next tool.

smcFanControl Menu utility for Mac. To manually modify the speed of your internal fans, you can install Hendrik Holtmann’s smcFanControl. For some of the older Macs that are still technically capable of running OS X 10.7 Lion, you may find that they are having some difficulty keeping up at times, and the default fan speed just will not provide the relief required. This menu bar item will allow you to change the minimum fan speed and effectively take control of just how fast your fan will blow. I created two custom settings: a midrange setting at 4000 RPM, and a high setting at 6000 RPM and will turn them on when I see things get a little too hot. I then set things back to Apple’s default levels once things cool down.

Purchase a laptop stand. Proper ventilation is key to allowing your Mac to cool down under normal conditions. Placing your laptop on a pillow or blanket because it is running hot may do more harm than good, especially if you end up blocking the vents that are trying to expel all that hot air. My personal favorite is the Cooling Bar from Just Mobile for $39.95US.  I find it convenient to carry with me and easy to set up.  Just Mobile has other stands for your MacBook as well. And if you tend to keep your Macbook closed when at a desk, consider Twelve South’s BookArc Pro for $49.99 U.S.

Let us know if you have other tips for keeping your Mac cool under pressure, or if you’re seeing temperature spikes under Lion that last beyond the first few days.