Why does the fan speed go crazy?

Hello,

I got the YLOD so I bought the kit on the site and followed the guide on ifixit.com. The YLOD was thankfully fixed BUT when I first turned it on and played a game, the fan started to spin faster and faster, becoming louder and louder until the system turned off. I reapplied the thermal paste since I read too much can cause that. After it doing the same thing happened when I turned the system on and played the game. I once more reapplied the paste (making sure to clean the previous amount each time) and this time made it thin. Now, whenever I turn it on, it almost immediately starts to spin fast and become very loud, making me incredibly nervous. Should I do the entire fix again or is this another problem with the amount of thermal paste to put on? I'm looking around to see if I can figure it out but thought I might as well ask here too.

Thanks!