Comment 2 for bug 864660

The overheating is probably due to the fact that you have a ATI Technologies Inc M92 [Mobility Radeon HD 4500 Series] graphics chip. ATI/AMD graphics have historically had only limited power management support under Linux. The good news is that better power management has of ATI/AMD graphics has now arrived!

Better power management for AMD/ATI Radeon R600 and newer hardware was introduced in the 3.11 linux kernel and refined in the 3.12 kernel. A PPA of the 3.12.6 kernel is available at http://kernel.ubuntu.com/~kernel-ppa/mainline/ and instructions on how to install and uninstall it are available at https://wiki.ubuntu.com/Kernel/MainlineBuilds

To use this power management for the AMD/ATI Radeon you will need to select it at boot by adding radeon.dpm=1 to your GRUB kernel boot options as described at https://help.ubuntu.com/community/Grub2/Troubleshooting#Editing_the_GRUB_2_Menu_During_Boot

If you have R700 or newer hardware (other than APUs) you will also need to install the latest AMD graphics microcode (ucode) files to /lib/firmware/radeon
These are available at http://people.freedesktop.org/~agd5f/radeon_ucode/
Get the version ending in "smc".

R700 basically means Radeon HD 4000 series and newer. However note that according to Wikipedia and http://xorg.freedesktop.org/wiki/RadeonFeature/#index5h2 the Mobility Radeon HD 4225/4250 is a RV620 chip, so anyone with one of those shouldn't need the updated firmware files.

Ubuntu 13.10 "Saucy Salamander" is based on the 3.11 kernel and includes the updated AMD smc firmware.

See the blog post at http://www.botchco.com/agd5f/?p=57 for further information.

Unlike the older dynpm method, the new DPM method works with multiple monitors and there shouldn't be any flickering as the performance level changes are handled by dedicated hardware rather than the driver.

The currently under-development 3.13 upstream kernel enables DPM by default (without needing the radeon.dpm=1 boot parameter I mentioned above) for Radeon HD 4000 through Radeon HD 7000 series graphics processors but with some specific ASICs being excluded.

Also make sure you have removed all dust from inside the computer, particulary from the CPU and GPU fans and heatsinks (on a laptop at the very least run a vacuum cleaner nozzle along the external air vents). You can also put the edge of a book under the back edge of your laptop so that it is raised off the desk at a slight angle, or purchase a laptop cooling pad (with USB powered fans) to sit the laptop on.