Late 2014 iMac 5k overhearting and shutting down?

In short, I noticed about a week ago that my iMac was “crashing” during video file transcoding. Basically I was trying to edit some gopro clips. When I looked closer I noticed that the “% CPU” in activity monitor was at 570+ whenever I transcoded any video files using either gopro studio or FinalCut Pro X. (If I manually stop transcoding the CPU % drops to normal levels) Also the iMac fan would ramp up to ludacris speed and eventually either the app would quit or the iMac would shut down and reboot. The failure reports make no sense to me but I suspect the GPU is failing and the CPU is taking on the entire transcode load.

My question is could this be an issue where just opening the iMac up and removing/cleaning and reattaching the GPU chip with thermal paste may solve the overheating?

any insight is greatly appreciated


You could install iStat Menus to see if it is a thermal problem.
It’s easier than tearing things apart only to find out it was something else.

1 Like

The whole GPU issue is NOT about removing the GPU and replacing the Thermal paste, but removing the Heat Sink from the GPU and then cleaning/reapplying the Thermal paste.

Please start with JohnAlt’s suggestion of iStatMenus to find what is the real problem first. Cleaning the dust/debris buildup is never a bad idea either.

I had a similar problem using OWC memory…

Thanks everyone. I took it off power, blew some air in the back vent and let it sit for a while. Booted up, tried some video transcoding and even though the CPU still went up to pretty high percentages, the fan didn’t ramp up as high and it didn’t crash. So it does appear dust is/was an issue. It’s been my video workhorse for 5 yrs now so I should probably open it up and clean it all up, repaste the heat sink as y’all suggested.

I guess the GPU on this just isn’t really meant for heavy lifting, watching it and the CPU max out is disconcerting but honestly this is the very first time I’ve ever monitored it. Here is a snap shot from activity monitor. I wish I could afford a new mac pro (or even an older one) but that’s not an option. Thanks again!!

This seems like a task better performed by the GPU.
It’s also a bit disappointing that Mac GPUs don’t work for CUDA.

That makes sense. I guess I don’t truly understand how the CPUs and GPU are designed to work. What perplexes me is the %CPU in the activity monitor going as high as 700% during transcoding, how is that even possible? I went to public school so I always thought 100% was it. Again I realize I’m just not understanding.

I remade a thermal paste on Macbook Pro 15 Retina 2012 after 6 years and even though I cleared it from the dust always after a year, this made a ton of difference both with thermals and fan noise.

Your CPU has multiple cores (4 in your case) and each core can run two threads. Essentially, it is several processors within one physical package. Since you’re running 700%, that would imply 7 threads working at 100%.

E.g. this dragster with 4 engines could run at 400%.

1 Like