Dell 8400 Blower Fan Replacement

I've read on these forums it can be done but you have to match the fans specs to exactly what that dell fan is Dells use a proprietary Heatsink and that ungly green looking shroud at least for the older Dimensions I don't know about the BTX models like this E521 we have but behind that shroud is a temperature sensor controlled and self adjusting speed case fan which blows the hot from the heatsink mand out the back of the case.  Back in the days of my Dimension 4400 they either used Datech or NMB fans.  I've heard the NMB fans tend to be a little quieter than the Datech ones.  If your system is still within warranty contact support and see if they will authorize a replacement fan you can request the NMB but there's not gurantee you'll get it.  The fan's label can be seen through the back of the case. If you're not within warranty either buy the fan yourself from Dell Spare parts or remove the fan yourself and get the info off of the label itself.  Just as a note the label doesn't always indicate that it's the area that should be facing back toward the case you'll need to test the system when you get the new fan.  Hope this helps.

Arghh! They never make it easy. I'll try the replacement fan route but I have a sneaky suspicion it won't quiet it down that much. Thanks for the input.

Well, I got the new fan unit and put it in. Marginal improvement at best. I think a better approach may be to put a baffle on the back with sound absorbing material to cut down on the noise. Shame I can't replace the fan with a non-OEM fan that runs much quieter, e.g. less than the 63 dBA the OEM fan runs at. The OEM fan also draws an outrageous 30 Watts!

The Dimension E521 that we have is very quiet you can barely hear the fan running I'm guessing that the BTX motherboards have a different setup as far as the cooling system.  I saw a pic of the inside of the case on the Dell website and I didn't see that ugly green shroud as opposed to the older Dells like yours.  I don't know if they use the PSU fan to do all the cooling or if there is a fan that only kicks on when needed.  I do feel air being drawn in from the vetns on the side.  Perhaps the old fan in the back of the shroud design couldn't be quieted so they went with this design. 

Latest update -  I couldn't take the noise anymore so I replaced the fan with a Silenx 92mm (Model IXP-64-14) and hooked it up directly to the PSU using a 4 pin Molex connector it came with. It fit perfectly where the old fan was. Even used the same rubber attachments. Oh the sweet silence! The Silenx puts out 42 CFM @ 14 dBA! I am using SpeedFan to monitor the HD temperature (Dell disabled the ability to monitor the actual CPU temp on the 8400...geez) and it is running only a degree or two hotter than with the old fan. I still have to hit F1 on boot-up to bypass the CPU Fan Failure message you get but it is a small price to pay for the awesome quite! I also replaced the thermal paste on the CPU heatsink with some  Artic Silver for good measure.

Okay, I am trying to modify the old Dell fan plug to bypass the CPU Fan Failure message. Based on my research there are four wires on the plug:

 

Red (12V)

Black (Ground)

White (RPM)

Blue (Regulator)

 

From the forum messages if you tie the Black and White leads together it's supposed to fake the BIOS out and bypass the CPU Fan Failure message. I tried this with no success. Is there something I am supposed to be doing with the other leads (which are open) or did I get the connections wrong?