Your Mac is a complicated beast. Whether iMac or MacBook, the Mac is loaded with all sorts of technology we’ll seldom see, but sometimes we’ll hear about it. Here’s a quick look at how you can monitor the temperature of components inside your Mac, why you’d want to, how you can control the fans that keep it cool (and sometimes noisy), and even check on the internal sensors. Most Mac users seldom bother with the internal sensors, have little need to control the fans, or worry about the temperature of various components. Until something goes wrong.
One of the first signs of a Mac that’s having trouble is the fan. When the fan comes on, something is happening. It could be nothing more than a Safari window with multiple open tabs connected to websites with a bunch of Flash advertisements. All the extra CPU juice that Flash requires can turn up the heat. Heat means fans. Fans mean noise.
Dec 25, 2008 Question: Q: Mac Pro Temperature control when using windows? Apple Footer. This site contains user submitted content, comments and opinions and is for informational purposes only. Apple may provide or recommend responses as a possible solution based on the information provided; every potential issue may involve several factors not. If you are running Windows on your Macintosh and need to change the fan speed, Mac & Boot Camp Fan Control can be a useful tool. Fan control System temperature Fan speed Fan Temperature Sensor.
How can you control the fans, monitor the Mac’s temperature, and check on the various and sundry sensors inside? Think temperature gauge. What this clever little utility does first is monitor your Mac’s innards– fans and sensors– and report on what it finds. Check out this list. TG Pro lets you view the Mac’s temperatures for each sensor; both current and maximum. That’s a good place to troubleshoot.
There’s more! You can also view the speeds and control the speeds for each fan inside the Mac. Set the fans to go to a certain speed (higher or lower) whenever it reaches a certain temperature.
There’s even a built-in sensor to notify you when the Mac gets too hot. The built-in diagnostics helps to locate faulty sensors and fans. And, as a good Mac app citizen, TG Pro can pop up a notification, or send you an email if you’re away. Setup and configuration will take a few minutes, though. There’s lots going on inside your Mac that most of us never both to learn about. TG Pro just makes it easier to control fans, monitor temperatures, and view sensor readings with a click. Nicely done, good reviews, and a great utility for any Mac user who wonders why the Mac’s fan keeps coming on.
TG Pro and smcFanControl as well monitors and allows adjustments to fans on my iMacs where Apple believes quiet trumps longer term chip life in certain climates. I live in a warm coastal community where very high humidity ~ 90% is the 24 hour norm in the summer months. 
Having experienced “unusually high graphics chip failure” (Apple’s words) 4 times on 3 iMacs over 7 years and replaced under AppleCare, I’ve concluded what Apple does to keep the iMacs quiet in the long term can break down the long term reliability of graphics chips and other heat sensitive components. If you stream video, Netflix, movies on YouTube or other streaming networks and experience jumps, excessive hangs, frequent pixilation or horizontal lines disturbing your viewing experiences, its “normal” activity at high humidity and temperatures. Higher/custom speed fan settings, permitted by third party programs is the only way to minimize these negative graphics results. Apple chooses to keep iMacs quiet.I choose to prolong the life of my iMacs chips (after the warranty periods) with minimized graphical interruptions.