PC fan running excessively

canalicomputers used Ask the Experts™
I've got a 3 year old Dell Optiplex 755 desktop PC which the fan is running excessively fast/high/noisey even though I've thoroughly sprayed out the dust from inside the PC case. What would cause this? Thanks.
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check the heatsink deep inside the fins for any dust. check for a bios update and chipset driver update.
I have found this to be a system board issue.  The thermostat is broken and always reads hot.  Usually need a new system board.
Most Valuable Expert 2015
What do you mean with "Spray"? Did you open the PC's case to clean out the dust? If not, make sure you open it, take a small brush and a vacuum cleaner then use the brush to loosen the dust and hold the vacuum cleaner nozzle some distance away so that it can gather the dust without sucking in other parts.

After that make sure the heatsink of the CPU is mounted properly, and also check if the fan runs smoothly when you try to turn it. Personally I'd remove the heatsink, then clean off all residue of thermal pads or paste from both it's and the CPU's surface, add a very small drop of fresh thermal transfer paste to the CPU's surface, firmly reattach the heatsink, then check if things are better.

If the fan doesn't run smoothly when you try turning it, replace it.

Also check the settings in your BIOS, many have functions that allow you to change how fans should run, and sometimes also a BIOS upgrade can help.
dbruntonQuid, Me Anxius Sum?  Illegitimi non carborundum.
Also monitor your temperatures.

Use a util look Speedfan http://www.almico.com/speedfan.php to do this and check if your temperatures are in the range expected for your CPU.

A noisy fan could be one that has worn out bearing.  Note rindi's comment on replacing.  If the fan is noisy at startup and then gets quieter after a period of time this is definitely a sign that its bearing has worn out.


I haven't tested the possible solutions above yet but all are very helpful, thanks!

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