Readers of The Apple Core remember the recent issue about the amount of thermal grease (or paste) that Apple applies to the chips in the MacBook Pro. There's pretty decent evidence that over-application of the paste is causing MacBook Pros to run hotter than they should. It appears that the same may be true for the MacBook.
A picture (right) from the official MacBook service manual posted on the MacNN forums clearly shows a MacBook being assembled with too much thermal paste on top of the chips.
To make matters worse, page 94 of the MacBook (13-inch) Take Apart manual says:
Although the amount shown appears to be plenty of grease, this is the correct amount that has been tested and verified on the production line.This over application of thermal grease on the MacBook and MacBook Pro flies in the face of the conventional wisdom about the correct procedures for use of the product. According to Wikipedia:
Because the thermal conductivity of heatsink compounds is so poor in comparison to the metals they couple, it's important to use no more than is necessary to exclude any air gaps. Excess grease separating the metal surfaces further will only degrade conductivity.
Heat Sink Guide also confirms the less-is-more approach to installing thermal grease:
You should apply a very thin (paper thin) layer on the heatsink with your finger before installing it. Don't use too much - the thinner the layer, the better.
It's not yet clear how many MacBooks are assembled with this much thermal grease or what the impact is on operating temperatures but it is clear that Apple is telling their service technicians to apply too much of the goop.