8. The heat (sink) is on
With the fan out, it's an excellent opportunity to check the CPU's thermal paste, which transfers heat from the processor to the heat sink and can dry out over time.
After loosening the four heat sink bolts [A], carefully slip the heat sink and the copper heat pipe out [B]. If the paste is dry, remove it with an alcohol wipe. Squirt a little thermal paste onto the surface [C], spread it out and put the heat sink back on top of the processor.
After wiping off any excess paste with another alcohol wipe, slip the heat pipe back into its place near the side vent. It should align with the heat sink just over the processor. Tighten the screws, making sure that everything fits securely.