How much Arctic Silver have you applied? If it spreads out
beyond the center half of CPU / heat sink interface, then you
have applied too much. Too much thermal compound causes less
cooling.

Chassis fan only determines interior chassis temperature.
It does not matter where air is bouncing around. Simple heat
equation makes that obvious. The temperature of incoming air
and the CFM of that 80 mm fan determines chassis temperature.
More air flow (more CFM) means cooler chassis. It does not
matter which direction air flows. CFM (amount of air moved
through chassis) and temperature of incoming air is only
important. However reversing fan direction can correct a hot
spot problem really created by improperly placed ribbon
cables. But ribbon cables will not obstruct airflow from a
CPU fan; change CPU temperature. Only importance of chassis
fans is that they all move sufficient CFM of cool air into
chassis. Nothing more.

CPU temperature is mostly a function of 'interface
changes'. The best thermal conduction involves minimum
material changes. Best conductivity is CPU direct to
heatsink. A thermal path from 'CPU to thermal compound to
heatsink' is less conductive. Thermal compound - least amount
possible - only fills microscopic holes. Compound must not
obstruct the larger number of CPU direct to heatsink contacts
- where best thermal conductivity lies. As noted, if thermal
compound spreads out into outer half of heatsink or farther,
then you have worsened thermal conductivity - caused
temperature increases.

Another thermal (material) interface is air to heatsink.
Don't concern yourself with this problem. That was
(supposedly) solved by your heatsink fan manufacturer. How
well he solve the problem is defined in a parameter discussed
two paragraphs below.

Critical to a CPU heatsink interface is pressure holding two
materials together. Heatsinks (properly manufactured) are not
perfectly flat. They are constructed so that maximum pressure
appears where almost all heat transfers - in the center - the
only spot that should have thermal compound. Having said
this, some heatsinks are not even machined. Instead, they
would place an inferior thermal pad or thermal tape so that
proper (and more expensive) surfacing is not required.

Better manufacturers will provide a parameter that
summarizes quality of this thermal interface: degree C per
watt. Most of those long winded reviews can be stripped down
to a table: degree C per watt. Any heatsink that does not
provide this number is suspect.

70 degrees is not really a problem since CPU can increase to
90 degrees without adverse effects. However 70 degrees
suggests your heatsink to CPU interface does have a minor
problem; or what is reporting temperature is not accurate.
Too much thermal compound or insufficient contact (pressure)
between heatsink and CPU could contribute. The one 80 mm fan
(that is more than sufficient to move necessary CFM out of
chassis) is not a problem as long as chassis temperature is
being reduced (incoming air is cool). Chassis temperature is
about moving air - cubic feet per minute (CFM) - nothing
more. Does not matter whether that airflow is from sucking or
blowing. Just that cool air enters. Cooling the CPU is about
an interface between materials and a very important parameter
called "degree C per watt".

As for Arctic Silver: expensive hype that is equivalent to
most every other thermal compound. Don't fall for their hype
as made obvious by missing specification numbers on every
Arctic Silver container. They count on you reading those
wordy articles rather than using a simple specification number
- so that you will spend ten times more money for equivalent
product.


Steven Campbell wrote:
I had the original CPU cooler on it then changed to Coolermaster
then changed to the Thermaltake SilentBoost. The SilentBoost is
rated up to XP 3400 and has got excellent write ups everywhere
I've looked. I'd gladly change it again if there was a cooler that
would do the job but I honestly think the one that is on it just
now is ok. What is concerning me most is that the temps have been
gradually getting worse. Can the Arctic Silver deteriorate that
quickly (8 months).

I'm going to bring the PC downstairs and clean it all and do as
Martin has suggested and turn the fan round first to see if that
helps any.