How to re-apply thermal paste on an iMac G5

August 18, 2020

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A few months back, I bought an iMac G5 from Goodwill for $16.50. It was listed as parts/repair with a flashing question mark on boot. When I received it, I found that there was no hard drive installed, so I installed a spare SSD I had. After a few days of fiddling with Open Firmware, I got it to boot from an OSX Leopard USB and I installed OSX 10.5 Leopard on the drive.

Leopard Install on iMac

After installing Leopard and making sure everything worked, I cleaned up the dark spots on the plastic case using a toothbrush. Then, I installed a few programs so that it could be more useful today. After this, I was able to use the iMac to do many different tasks, but I quickly found out that it was running quite hot (70 to 75 degrees celsius). Because of this, the fans would ramp up, making a lot of noise. During tasks that used a lot of CPU, the machine would almost become unusable. So, I decided to dust out the computer and replace the thermal paste. Below is a comprehensive guide to removing the logic board and replacing the CPU thermal paste. I hope you enjoy!


  1. Begin by shutting down the iMac and removing the power cable & peripherals
  2. Then flip the iMac over and carefully set it down on its screen
  3. Unscrew the three bottom screws until they no longer turn. They won't come out all the way, but you should unscrew them as much as you can.
  4. Fully remove the back cover
Removing the back cover
  1. Next, remove both sticks of RAM by unlocking the locks and pulling them straight out
Removing the RAM
  1. Remove the three Philips head screws holding down the optical drive
  2. Pull up and out to remove the optical drive
Removing the optical drive
  1. Turn the middle bottom screw clockwise to free the power supply
  2. Remove the three screws along the top of the power supply
  3. Pull the PSU up and out, and remove the logic board power connector


Removing the PSU
  1. Disconnect the HDD thermal sensor cable from the sensor board
  2. Remove the two screws holding in the fan duct
Removing the fan duct
  1. Remove the two screws holding down the fan cover and lift it out
Removing the fan cover
  1. Remove the two screws holding down the display cable and disconnect it from the board
Removing the display cable
  1. Disconnect the SATA power and data cables from the logic board
  2. Disconnect the two fan connectors
Removing the SATA cables
  1. Slide out and disconnect the inverter to display cable
  2. Remove the screw holding the inverter in place
  3. Pull straight upward to remove the inverter, and disconnect its cable from the logic board
Removing the inverter
  1. Remove the lower fan and speaker connectors by using a spudger to pull straight upwards
Removing the speaker & fan cables
  1. If you have an airport card installed, pull up on the tab and remove it
  2. Remove the Torx screws on either side of the airport slot to access the modem card
  3. Remove the two T6 Torx screws holding in the modem, and pull straight up to remove it
Removing the modem card
  1. Now, remove the 6 T10 Torx screws and 3 Philips head screws to remove the logic board
Removing the logic board screws
  1. Pull straight upward to remove the logic board
  2. Set it down gently so you don't damage any components
  3. While the board is out, clean the heatsink and blow out any dust to improve cooling
Removing the logic board screws
  1. Turn over the logic board and clean the old thermal paste off the CPU using isopropyl alcohol and a q-tip/paper towel
Cleaning off the old thermal paste
  1. Now clean off the residue from the heatsink on the front assembly of the iMac
Cleaning off the old thermal paste
  1. After cleaning off the paste, apply a glob of paste to the CPU and spread it evenly
Applying new thermal paste


  1. Replace the logic board in the case, making sure to line up the attachment points
  2. Screw in the 6 T10 Torx and 3 Philips screws that hold in the board
  3. Replace the modem card and screw it in
  4. Replace the airport card holder and the airport card (if installed)
  5. Push the lower fan, speaker, and mic cables back into the board
  6. Attach the inverter cable to the logic board, and reseat the inverter
  7. Screw in the Philips screw holding in the inverter and re-attach the inverter-to-display cable
  8. Connect the SATA data and power cables to the board
  9. Connect the upper fan connectors to the board
  10. Reseat the display cable and screw in the two screws holding it in
  11. Re-position the fan shroud/cover and screw in the two screws
  12. Screw in the two screws holding the fan duct to the heatsink
  13. Use a spudger to push the HDD thermal sensor cable back in
  14. Replace the power supply into the case

You may have to pull the bottom of the case so you can fit the PSU

It also may take a while to replace the PSU, so be patient and careful with the components nearby

  1. Screw in the PSU screws, and turn the middle bottom case screw counter-clockwise to lock it in place
Partially reassembled iMac
  1. Replace the optical drive by pushing the white alignment things into the case and then pushing the back of the drive onto its connector. It may require a bit of force to attach the drive to the connector
  2. Screw in the three Philips screws holding in the drive
  3. Push in both sticks of RAM until the locks click into place
  4. Align the back cover and reseat it onto the case
Partially reassembled iMac
  1. Screw in the two outermost screws on the bottom case until they no longer turn
  2. Make sure everything is secure and stand the iMac back up
  3. Great! You're done re-applying thermal paste on your iMac G5


Partially reassembled iMac

After re-applying the thermal paste and thoroughly cleaning out the fans/heatsinks, I was able to reduce idle temps from ~50 to ~45 degrees Celsius. Under load, the effect was even more profound: temperatures were reduced from ~75 to ~60 degrees. The fans weren't as loud, and didn't kick in as often. During simple text editing and simple terminal work, the system was completely quiet. During tasks like heavy web browsing, watching DVDs, etc, the system was a lot more usable due to lower temps. If you own an iMac G5 and you've never changed the thermal paste, I highly recommend that you do this. It's a fairly straightforward process that yields great results. If you want more posts and/or videos on the iMac G5, make sure to comment down below. Thanks for reading!


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