This PIII850E that before was 100% stable at 133MH FSB in our watercooled rig (here) were not stable anymore ! This rig had been running for ~ three months. I didn't even notice that the temperature had raised since it happened gradually. After a bit of investigation I found that the water temperature had raised almost 10'C ! Why ?

Dust blocking up the radiator ! I didn't belive my eyes when I saw this. The room where this rig is located is vacuumcleaned / and the floor is washed two times a week.But this fan/radiator is installed down in the front of the AopenHX08 cabinet and is sucking every piece of dust at the floor in.

This is the top radiator - the dust has passed through the lower radiator, and there were of course a lot of dust inside the cabinet as well.

More :

This is a Alpha heatsink :) -- after cleaning the temperature dropped ~10'C !

Update:

A year ago I built a rig for a local guy : he called me after he had seen this article and told me that he has checked his puter for dust build up too. I grabbed my camera and payed him a visit :

GoldenOrb : filled with dust - after cleaning the temperature of this PIII550 slot1 dropped ~8' celsius.

And his "hairy" GeForce cooler :)

We contacted our sponsor 3DfxCool / GlobalCool and asked if they could start to sell filters, and they agreed after we sent them the pictures. These filters which are easy to clean and lasts forever are really a good investment. Regular checking for dust in your cabinet is still recommended. Take care if you use a vacuum cleaner to remove the dust - static electricity might be present. We used compressed air to blow away the dust from the cooler and his GeForce. 

None of these pictures are arranged in anyway !