The only way to successfully prevent a YLOD due to overheating (if it's not too late already) is to disassemble your PS3 and replace the thermal compound. All other suggestions in this thread won't help/make it worse. If you turn it back on before replacing the thermal paste, then your PS3 will almost certainly die very soon.
I suggest you use Arctic Silver 5 thermal paste. It's what I did and it works great (though I did it BEFORE my PS3 ever started acting up).
"Well certainly with the Xbox 360, we had some challenges at the launch. Once we identified that we took control of it. We wanted to do it right by our customers. Our customers are very important to us." -Larry "Major Nelson" Hryb (10/2013). Note: RRoD was fixed with the Jasper-revision 3 years after the launch of 360
"People don't pay attention to a lot of the details."-Yusuf Mehdi explaining why Xbone DRM scheme would succeed
"Fortunately we have a product for people who aren't able to get some form of connectivity; it's called Xbox 360,”-Don Mattrick
"The region locking of the 3DS wasn't done for profits on games"-MDMAlliance
