This instructable is for the DELL 745 Small Form Factor - SFF. It might work with other DELL SFF machines.
The 745 Dual Core is a Great machine, but the cooling fins of the video card sit right below the HD, there is very little good ventilation and only one fan in the case. My 745 HD was getting up to 140 deg F...Ouch!
Tools: You will need an 80x80x25 mm 12V computer cooling fan. This fan perfectly into the back of the case, no screws or glue needed. I used a 1.92 Watt model, low draw on current, but high volume air flow. You can wire the fan to the 745 power supply, or use an external power supply. This will require the usual wire splicing and joining.
Disclaimer: This Instructable assumes that you are comfortable and competent working on your own PC. Do not do any of these steps if you can't take PC components apart, and re-assemble them in working order. If you break it, you bought it.
Step 1: Remove the Hard Drive
First, unplug and remove all the input wires, cables etc. Open up the case and remove the HD and the extra video card. The computer should look open like in the photo.
Step 2: Bend the Tab
The latch that releases the extra cards has 2 tabs/pins. Pry the holder off of its tabs, then just bend the aluminum tab...it is not difficult, but use care.
Step 3: The Bent Tab
Here is a photo of the bent tab
Step 4: Install the Fan
Next, take your fan and just press into the opening created by bending the tab.
I found that placing the fan pointing OUT, sucking air OUT of the case did the best job of cooling the HD.
Step 5: Wire the Fan
Wire up the fan to a remote power supply, or the computer power supply.
I used a 12V/1.92 Watt fan straight wired to a 12V output power supply. The power supply plugs into the computer power strip which is convenient. You can unplug the fan if needed.
You could also wire the fan to the computer power supply. Its your choice, we do not have a lot of current draw here.
Here is the final fan installation at work. It has lowered HD temps up to 30 degrees and operator stress a corresponding amount.
For what its worth, I also leave the side of the case open in extreme room heat conditions. This introduces some dust, but it sure runs cool.
Thanks for checking out this Instructable. If you are interested in e-bikes, check out my other instructable: https://www.instructables.com/id/DIY-Electric-Bike-Conversion/
and for info on Electric Vehicles: http://www.evsroll.com