If I remove the heatsink/fan...

[sullonone]

do I have to take the old thermal paste/pad off or can I just screw it back down?

edit for clarification: I took my heatsink/fan off to clean it. Does that ruin the old paste? Do I have to clean it off and reapply or can I just leave it on and reassemble?

 

[kivan2400]

You can still use the old one yeah should not be a problem

it would if it was 2 different pastes, but if the heatsink is clean and there is paste on the CPU then it should work as normal

 

[jaguarskx]

Anytime you remove the heatsink it is highly recommend that you clean it and the CPU and reapply a fresh thin layer of thermal paste.

Removing the heatsink breaks the thin paste layer which helps improve heat transfer. It introduces air pockets and that acts as a heat insulator rather than a heat conductor.

 

[Motopsychojdn]

^+1 You take it off, you clean and re-apply new paste
Moto

 

[beanoslim]

Clean it thoroughly and re-apply fresh paste do not re-use.
http://www.arcticsilver.com/methods.html

 

[sullonone]

Thanks so much all!!

 

[lamar5559]

It should still work.
You should change the thermal paste\pad every few months, but if you already did in the past few months, you should be good.

 

[beanoslim]

Yes you can re-use pads but not paste, if it has a pad I'd remove it and use paste anyway.
You don't need to re-apply paste every few months just when needed, like your cpu temps rise.