I'm suffering from the excessive CPU use from kernel_task
If you can I would recommend setting up Time Machine on your system. If/once you have a backup of your files then my suggestion would be to use Onyx http://www.titanium.free.fr/ for your OS to clear out some caches, logs, and day to day junk that piles up. 

Getting rid of logs, caches, and Spotlight indexes can help your system repair itself. 

Once Onyx has run its course and the system has rebooted wait for spotlight to rebuild and see if kernel task still is eating up your CPU. If it does then I would recommend reinstalling the OS. (That's why I like making sure you have a backup of your files before hand)