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[Confusticated]

Proper copper heatsinks are an obvious but smart move providing you don't mind either re-boxing the plug or ripping out the power supply to make the necessary room.
You will need to be careful about the SoC, as the centre of the chip is recessed (the silver disc area in the pictures) and requires a matching heatsink which may be difficult to obtain.
The Phy chip drives the Gb Ethernet ports, and is responsible for a considerable amount of heat when active. Luckily the top of the chip is flat, almost any copper heatsink (cut to size) could be glued on with proper thermal resin with a good result.

Yes, (and no) I have a digital food thermometer in my computer toolbox which I have used for years on conventional computers. It is not possible to use it on the Guruplug with any
degree of accuracy.
For long term, I am currently investigating using a one-wire temperature sensor.
For short term, I am considering attaching thermistors in a few critical places with flying lead to the outside world so I can attach a multimeter.
I can then comparatively measure the temperature (within 5%) by heating up an identical thermistor attached to my digital thermometer until it yields the same value.

Don't loose sight of the facts.....
The Guruplug creates approx 5W of heat (previously in a confined passively ventilated space, causing thermal runaway) that is what needs to be removed, not the 75-120W of a conventional desktop cpu.

[apemberton]

I noticed that with the kernel 2.6.35.7 I have installed on my GP's have a fancontrol module which is started at boot time. I have no idea of its configuration or use. Since there are no publically available datasheets for the Marvell Kirkwood (AFAIK), I have the feeling that is as much use as a chocolate fireguard. It would be nice to use it with a fan though. I'd still like passive cooling to cut down noise though. It would be good to harvest the heat too.

[kleptog]

Proper copper heatsinks are an obvious but smart move providing you don't mind either re-boxing the plug or ripping out the power supply to make the necessary room.

When I read this I didn't quite understand, but then I didn't realise quite how little space there is between de CPU and the power supply. But you're right, it's only 5W, so maybe even a small heat sink with the fan set to a low speed will be sufficient.

I got a tip from someone about something called an LM35, which does temperature measurements in a single chip and can be read out using an ordinary voltmeter. Seems like it might be a simple solution to the temperature measuring problem.

[sfzhi]

Since there are no publically available datasheets for the Marvell Kirkwood (AFAIK)

All you have to do is type "88F6281" in Google search.

[apemberton]

OK Thanks. I guess Marvell have split the hardware datasheet from the software model datasheet and of course the ARM9 core will be on the ARM site.

[Confusticated]

Cut vents through the power supply partition...

[Confusticated]

So air may flow out past the PSU components...

[Confusticated]

Solder a sub-miniature red LED in series with the fan...
(I socketed mine to make it easily changeable, you don't need to)

[Confusticated]

Cut an inlet port in the top of the plug and fit the fan...

[Confusticated]

NOTE: Position the inlet carefully so that it includes all three chambers made by
the natural dividers of the power supply insulating material, and the daughterboard.  

[Confusticated]

Not an ugly plug, but not silent either. The fan may sound awful to start with as
the ball bearings rattle around, a couple of hours running and it should settle down.

The problem is, in a nutshell, the ball bearing. A sleeve bearing fan running  at this
super-low speed would be perfectly adequate cooling wise and last years, it would
also be silent. I have not taken temperature readings yet, as no external part of the
plug gets warmer than my hand, there is no point until I can 'glue' probes to the
chips themselves and run it with the case closed..

The cheapest 20mm fan I have found available to non-trade (orders less than 1000)
is £15. If anyone knows different, or of something that contains a 20mm fan that
can be bought cheaply, please post.

[kleptog]

Thanks for the images, I hadn't thought of those possibilities.

I've done some measuring and it seems that while the fan is important, it doesn't need to do much at all. The difference between the fan running full blast and barely audible is (so far) about 5 degrees. Completely off is a separate category altogether and a lot harder to measure.

Cutting a hole in the topside where you put the fan seems to me to be an excellent idea I was definitely considering that. What I'm interested is is what you used to cut the plastic? I haven't been able to determine the type of plastic so I'm not sure which tools I can safely use on it. (I'm not a hard-hacker usually). Those are some very nice holes you've made there.

I've looked for heatsinks but I have not found any small enough. 5mm high is about the minimum and that really places you right against the power supply, which doesn't seem like a good idea.

I'm hoping to finish my temperature measurements in the next few days (there's never enough time) so I hope it will help people out.

[Confusticated]

All work was carried out with standard household tools, there are three techniques you could try.

1, Melt/burn it out with a soldering iron (messy and smelly).
2, Mark a circle and drill lots of 3mm dia holes around the circumference
    and then file it out smooth (the Dremmel approach).
3, Attach a hole cutter to the end of your household DIY electric drill (and live dangerously).

I, of course, chose number three.

[Confusticated]

My GuruPlug is not a hairdryer....it is now in fact almost silent and running cool.

I have swapped out the fan for another, at a different size of 25x25x10 @ 5v.
The 10mm dimension permits the manufacturer to use a slightly better bearing.
I have to get to within 150mm of the plug to be able to hear the fan at all.
Result! 

[Rexyboy]

Hi,
After reading through a few Guruplug cooling threads I decided to make a few simple changes myself.  I am now running a 40x40mm fan which is cool and silent (until you put your ear against it).

Below are a few photo's.  If anyone is interested in the details, let me know.