Does thermal paste go off?

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OK - I've noticed lately that my CPU has been running hot (> 50C) -
Athlon XP 2400+ - not overclocked. Decided a few weeks back to clean
all the fans, which helped a bit, but not much. I assumed the
unusually high ambient temp here in the UK was to blame, but it's
been cooler today and the CPU was still getting up to 60C when idle
in the H/W monitering tab of the BIOS.

I checked the heatsink for a good contact and found it slid a little,
so I took it off and the thermal paste is very soft and thin in
places. I've smoothed it out a bit and the temp is down to 51C, but I
reckon it's time to replace it.

Assuming it's no longer effective I need to clean the paste off the
bottom of the heatsink and the processor - but what's the best way to
do this?

And should I go for paste or pad as a replacement?


Re: Does thermal paste go off?

  Appreciate how a thermal interface works.  With every medium
change, then thermal resistance increases (thermal
conductivity decreases).  The best interface is a direct
heatsink to CPU contact.  Add thermal compound and you have
added another medium change.  However not all the heatsink
will contact CPU.  Some microscopic air holes don't conduct
heat well.  So we fill those microscopic air holes with
thermal compound.  This stingy (extremely conservative)
application should cause a less than 10 degree temperature
reduction - if heatsink was properly machined and attached -
compared to heatsink with no thermal compound.

  If you have so much thermal compound that CPU is sliding,
then grossly too much thermal compound was applied; heatsink
does not contact CPU directly. IOW you have decreased thermal
conductivity (increased thermal resistance).

  Thermal compound should be applied so sparingly that it
never squeezes to the outer CPU / heatsink interface edge.
Furthermore, excessive thermal compound can cause electrical
problems. Just another reason why thermal compound should be
applied grudgingly.  Too little is not a problem.  Too much
can cause increased temperatures AND electrical problems.

  Most important - most of heatsink must contact CPU
directly.  Therefore heatsinks (properly machined) are not
perfectly flat.  A properly machined heatsink maximized
pressure in that center section where most heat is
transferred.  IOW your heatsink should never slip.
Insufficient pressure is on the critical CPU / heatsink
interface means a CPU could slip.

  Those who first learned numbers will appreciate why cleaning
dust in fan and installing a stronger fan causes minimal -
almost insignificant - cooling.  Those who first learned basic
concepts also demand the most critical number for a heatsink:
'degree C per watt'.  If a heatsink does not provide that
number, well, they may also hype thermal compound so that you
don't learn about a CPU / heatsink interface not properly
machined.  It's called cost controls rather than product
design.  Lesser products cannot be bothered to provide 'degree
C per watt' because of who they are marketing to.  These same
people also hype Arctic Silver and the Tim Allen concept of
"more fans".

  Immediately, if a heatsink is slipping, then the heatsink
was not properly pressed to the CPU.  If thermal compound has
squeezed out the side, then grossly too much was applied which
would only increase CPU temperatures AND may cause
intermittent crashes do to electrical problems from too much
thermal compound.

D-Dan wrote:
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