2009 iMac - overheating GPU

[homsar]

Hi

my 27” 2009 iMac has started overheating. A few minutes after boot the fans spin up to maximum and never spin down. Looking at iStats, the GPU die and heat sink are both very hot—80-100 degrees C, with the die temperature being the hotter of the two and flashing red in iStats.

I’ve tried cleaning the GPU and heatsink and reapplying fresh Arctic Silver, but no change. The temperature gradually increases over the course of 15 minutes. I don’t see any visual corruption at all. I can’t see any processes using significant resources that would be stressing the GPU. (Just cloudd and mds_stores being busy as I’ve not touched the machine in a year while waiting for time to try re-pasting it.)

Weirdly the system goes straight from no audible fan to maximum, jet engine taking off level fan. (I’d have expected it to gradually increase fan speed as the GPU temperature got hotter? But even at max fan speed, it can’t seem to get the GPU temperature back down.)

Is this a sign that I need to replace the GPU? Or bake it to reflow it? Or is it some other problem that’s more easily/less expensively fixed? (I can’t believe how expensive GPUs are currently even for such an old system)

Many thanks in advance for any tips!

 

[pigoo3]

Yes those temps are pretty darn high.

Launch the app called "Activity Monitor" (usually in the "Applications > Utilities" folder). Click on the "CPU" tab (if it isn't selected already)...and take a look at the "%CPU" numbers. With the temps you're seeing...I'm going to guess you should see some pretty high numbers!

One thing to try is booting into "Safe Mode"...this may eliminate any "rogue" items trying to run.

A 2nd thing to try is boot the computer from a 2nd storage device (very likely an external HD with the macOS installed on it). Could also create a 2nd partition on your internal HD...install a fresh copy of the macOS on it...and boot into it.

Since your iMac seems to be running ok since no other issues were mentioned (other than high temps & high fan speed)...I'm guessing something is up with the the macOS install.

HTH,

Nick

p.s. Welcome to Mac-Forums!

 

[homsar]

Thanks Nick for the suggestions. Safe mode doesn’t stop the escalating temperatures, and Activity Monitor shows occasional bursts of activity from iCloud processes but nothing untowards. I’ll try booting from an external disk when I have time to set one up.

 

[pm-r]

my 27” 2009 iMac has started overheating. A few minutes after boot the fans spin up to maximum and never spin down. Looking at iStats, the GPU die and heat sink are both very hot—80-100 degrees C, with the die temperature being the hotter of the two and flashing red in iStats.

Are the appropriate cooling fans operating properly???

You could try changing various speeds and settings using Macs Fan Control to test,

Macs Fan Control - control fans on Apple computers, also on Windows via Boot Camp

Control fans on Apple computers, also on Windows via Boot Camp. Monitoring of fan speed and temperature sensors. Solve fan noise and overheating problems, iMac HDD replacement

crystalidea.com

or even use Tech Tool Pro.app Test Fans option module if you have or use it.


- Patrick
=======

 

[homsar]

Thanks Patrick for your reply. I've tested using Macs Fan Control and while the HDD fan is a little rattly, all three fans spin up when I tell them to.

I believe the ODD fan is the one closest to the GPU. By the time I got Macs Fan Control installed the GPU was at 65°C; setting the ODD fan to maximum (3800RPM I think) would hold the temperature there. Setting it back to Auto then caused it to continue getting hotter to 75°C; again, setting the ODD fan to maximum would stop it getting hotter.

Something I hadn't noticed previously is that the CPU temperature was also gradually increasing, getting as high as 80°C, but turning the CPU fan to maximum did bring this back down. For some reason the system isn't spinning up its fans until it gets pathologically hot?

I also tried using a freshly downloaded Ubuntu live USB (to eliminate any possible macOS problems). By the time I got the system booted and the lm_sensors package installed, the GPU was already at 100*C and the ODD fan was at full speed. Similarly to running macOS, the fans were silent until suddenly they span up to full speed just as I was about to check the GPU temperature.

 

[chscag]

All indications of a failing GPU. Not sure it's worth it to change out the GPU module and heat sink in your 2009 iMac, but maybe you can find a replacement at a decent price on eBay.

 

[homsar]

Thanks—I've set up a saved search on eBay, but prices are currently sky-high. Hopefully they'll come down eventually.

 

[jocarot]

baked the gpu, that works for my daughter's Imac. Still running after 2 baked gpu.

 

[Procrastinus]

Problem is in the design of the top air vent. It is too small as a heat outlet - beauty over practicality?
One nuclear option is here https://youtu.be/W4ldLHYTtec
I did a simple similar mod to increase the rear cover opening on a plastic backed iMac and it runs way cooler.
But with an aluminium back........