My Y400 ran into some trouble a while back and still isn't fixed but I won't tell what happened to it here as I will post it on a new thread. Simply put, I had to mod the laptop fan so that it would run at 100% speed no matter what. It made the fan run louder but made my temps considerably lower. This is a post to show you how I did the mod.
1. Open up the bottom cover of your Y400 or Y500
2. Locate the cables for the fan.
3. There should be four cables there. One red, one black, one yellow and one brown.
4. Cut the brown wire. The brown wire is for the motherboard to control the fan speed. Once you cut it your laptop fan will run as fast as the dust cleaning process lets it in lenovo's energy management tool. This is the fan's normal speed. It was made to run slower by lenovo to make less noise.
I got the image above from this thread: http://forum.techinferno.com/lenovo-ibm/2773-y500-disassembled-pictures.html
It shows roughly where the cables should be for the Y400 and Y500.