Ok, I have fixed three PS3 systems that have had the "YLOD"...
The easiest way to explain how to fix "YLOD", is this;
1.) Take apart your PS3 (all the way).
2.) Locate the two main processers,(the two biggest chips, under where the fan goes).
3.) Use a heat gun,(not a hair dryer), to "reflow" the processers by warming both chips for about 15-20 seconds each. (*) After you have heated up the processers, DO NOT TOUCH OR MOVE THE MOTHERBOARD FOR AT LEAST 15-20 MINUTES!!!!!!!!!!!!(You will break your motherboard, and be SCREWED!)(*)
4.) Use Thermal Compound on the tops of the 2 processers,(enough to spread a thin layer over the entire two chips).
5.) Carefully put your PS3 back together, and Boom...Your good to go!
Just so you know...
60gb, 80gb(v.1), 20gb are the models I've fixed. I don't know the hardware of any newer models.
You must be very careful while trying this! You can, and will fuck up your PS3 forever if you mess up!
I am NOT responsible if anyone does this and breaks their shit!