Avoid using rubbing alcohol which is just 70 ipa.
Clean heatsink thermal paste.
Ipa 90 concentration or greater to clean the thermal paste residue off the thermal contact surface of your heat sink.
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Clean out the heatsink and cpu then apply a very thin even coat of thermal paste on the cpu.
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Thermal paste can sometimes harden which greatly reduces its effectiveness.
Use a coffee filter or a lint free cloth and a little isopropyl alcohol a k a.
Looks like you have no ventilation.
If this is the case you will need to remove the old thermal paste clean the surfaces and then re apply new thermal paste.
Note that if you remove your cpu cooler for any reason you should always apply new thermal paste.
Macbook pro 15 unibody early 2011.
Inspect it for any thermal paste where it came into contact with the heatsink.
But since air is a notoriously poor conductor of heat.
If you find any use the same steps to clean the surface.
Remove the heatsink depending on what kind of heatsink you have flip the latch or release the retention clips that keep the heatsink attached to the cpu.
Chances are if you ve noticed an increase in temperature over the years it s due to the paste drying out.
Replace the heatsink careful to put it straight down on the cpu.
Wipe away most of the thermal paste that you can and then use 99 pure ipa to clean away any residue.
Thermal paste can get mighty hard depending on how long it has been applied for.
I usually keep the heatsink as level as possible when i put it back on and tighten the screws little by little in a star pattern like lugnuts on a car.
I like to use kimwipes as they leave very little lint.
However if you use a spudger to scrape the old paste away only use a plastic one to reduce the chance of scratching or otherwise damaging parts.