Why does my iMac freezes up intermittently? My iMac freezes up intermittently. The cursor can be moved but nothing responds. I just have to shut it down and restart. It's been doing this before and since my hard drive failed and was replaced. I'd also increased my memory from the original 4GB to 12GB thinking that was the problem.  But neither the HD replacement or the memory upgrade changed anything.  I can go for days, sometimes or a week or more without a problem. Then it'll freeze a couple of days in a row, or even twice in one day.

It's a late 2009 27" iMac, running Mavericks 10.9.4.
It could be that your iMac freezes because some component is getting too hot (in my opinion  Apple’s temperature thresholds are not setup for reliability, but rather for “comfort”). 

You can list temperature sensors with:


iStat Pro (free, discontinued widget, but runs on High Sierra without a hitch)
Macs Fan Control (paid app)