Yes! you must remove the heatsinks. I dont know why either but it sounds right
The way I do it is..
Insert mobo into tshirt, arrange it so that either open ends leave some of the motherboard showing but cover up all the capacators. (leave areas like GPU/CPU Hana Ram exposed)
Tape the Tshirt into place, then wrap tinfoil round it. Then turn the motherboard 90 degrees and wrap more tinfoil the other way so it closes up the gaps at the sides.
Pad it all down gently so its not flapping about then make a big hole in the foil in the same areas that you left exposed before. Top and bottom.
Stick it on a baking tray sideways so that there is a gap underneath and put it in the oven with the Eject and Sync buttons toward the front of the door. They tend to melt if they are at the rear.
Leave for 15 mins gas mark 7 ( I used to do 10 but extended it to 15) Then once it's done I take it out very carefully and put it down and leave it to cool down.
I ususally do something like clean heatsinks or flash and clean the dvd drive while im waiting.
Hopefully after all that it should last more than a few hours, HTH.
