Q My iMac seems to be running a bit hotter than usual, despite keeping open software to a minimum. Is there any monitoring software you recommend and is there a list of expected operating temperatures anywhere?

A The best monitor is Hardware Monitor from although a lot of utilities now include this feature. There are several in the Mac App Store, including Bresink’s excellent System Monitor (£3.99).

Comments Typically, processors should run around 40-45˚C; anything over 50˚C starts getting worrying.

If your model has additional sensors covering bridge or graphic components in chipsets, they often operate significantly warmer, perhaps more towards 60˚C, although it is good if they remain rather cooler than that.

Some Macs also monitor hard drive temperatures, which are most useful, as failing hard drives tend to run hot, well over 50˚C. Unfortunately I don’t think that any iMac has a suitable sensor for that, although some Mac Pros and older server models do.

If you think that your iMac’s temperatures are on the high side, and the fans are running normally, then it would be worth shutting it down, turned the mains power supply off (but leaving it plugged in so that it is still properly grounded) and giving it a good clean, particularly around any cooling vents in the case.

If it runs persistently hot, or you cannot obtain temperature measurements from it, it is worth getting it checked out at a Genius Bar or by an Apple-qualified engineer.