Dell 7920 suffers from serious  thermal management designs.

That bulky shroud is inefficient and cannot cool down the CPUs correctly, specially the second CPU. Hot air from the first CPU blows to the second CPU, which is a stupid design. Tight spacing for CPUs would not allow to use other available aftermarket 3/4U heatsinks. So you are stuck to the original heatsinks or you should downgrade to some noisy 2U heatsinks for slim servers. 

Similar to what you explained, I also experienced the high temperatures around 80-88 during full CPU load.

However, I managed to reduce the temperature to around 75 at full load by installing two 80mm fans ; one at the  rear end of CPU1 and the other one at the inlet of CPU0. Also, I have increased the fan speed to 10% in bios. With those changes, the temperature of both CPUs stay around 35 at idle to 75c at full load, which I think is reasonable. 

Using hwinfo64 or speedfan was problematic because the fan speed could not be automatically controlled using pwm fan controllers. This is mainly because the controller in those software only allows for 3 levels of rpms. Also I experienced some BSOD using those software.

Hello Rain_HH,

Can you possibly share photos of how you mounted the fans? I know I will screw this up somehow. Did you use a PWM splitter maybe from 4pin to 1X4pin + 1X3pin 

Any help is appreciated. There is not a lot posted on this subject except people complaining. 

I had the same probem with my Precision 5820 and more problem after i''ve added the RTX3090. But i found a good sollution. How the Dells fans at 100% have a huge noise, i replaced the Dell fans by Noctua Fans. How noctua fans are more sillent, i put the Fan Controller to maximum speed and now i have a processor temp at 68ºc in maximum charge or 30ºc at standard use.

And my RTX 3090 in maximum charge, the temp is 70ºc.

But caution! If you change your Dell fans by noctua fans you will need the adapter because dell fan connections have a diference sequence from standard connections!

Thanks for that advice. I will look into that as well.

Hello picasso567,

I am running some costly simulations, and cannot open the computer now, but will post some pictures later.

This is what I did to reduce the temperature (it is a bit different from what I posted before):

1. I bought a 5V 80 mm Noctua fan which comes with a USB adapter (80x80x25mm). 

2. I bought another 12V 3-pin 80mm slim fan (80x80x15mm):

https://www.memoryexpress.com/Products/MX75213

or, even better (but noisier) fan: DSTIME-80mm-3-PIN-Brushless-Cooling

3. Some rubber bands or plastic zip ties

4. A 5pin to 4pin fan adapter from Amazon

------------------------------------------------------------

I realized that the major issue is with the temperature of CPU1. So I mounted both fans on the heatsink of CPU1. I left CPU0 as is because when I raised the minimum fan speed to ~10% from the BIOS, the temperature for CPU0 is OK by itself (~73 at 100% load).

Anyways, I placed the 80mm USB fan (Noctua fan) at the downstream of the of heatsink CPU1 to suck the air and the slim CPU fan at the upstream end of heatsink CPU1 to blow the air (the upstream end is facing the BIG middle fan in the air shroud ). I used the rubber bands to tighten the fans to the heatsink of CPU1. You could use a zip tie, but needs a bit of work to properly close the air shroud.  I connected the 5v Noctua fan to the internal USB port, and the slim 3-pin fan to the fan header for CPU0 using the adapter.

Note: I had to use a slim fan for the upstream end because the big middle fan would not give enough space for another 80x80x25mm Noctua fan. So this way, both fans (the USB fan and the 3pin fan) are working at their full speed always without adding lots of noise. Both fans were relatively quiet. I always look at the Air Flow and Noise level when buying fans to ensure enough air can be blown with small noise. (although, the slim fan does the same job as the big middle fan in the air shroud, but at low minimum fan seed set in the BIOS, the amount of air provided by the fan in the air shroud  is not enough to properly cool down the CPU1. Using this dedicated fan more air flows directly into the heatsink1)

Note: I could use a Y-splitter to attach two 12V PWM fans to CPU1 header - 3 fans to one header (i.e., the middle header where the big fan is installed)-, but there are some concerns: first you have to ensure that the fans would not draw a lot amperage from the same header, secondly the RPM of the fans should be enough. I realized that when you use PWM fans, the RPM would not increase a lot unless the temperature is above 85 ish which is not ideal. Therefore, I have used two dedicated full speed fans with low noises. 

Note: You can increase the minimum speed of the original fans (CPU zone) to above 50-70%, and ignore this modification, but the system becomes noisy and inefficient. That was the reason I used this small modification to add two 80mm fans. 

Note: I have tried almost all available aftermarket active heatsinks (like 2 and 3U Dynatron). But either they won't fit or the temperature reduction was not substantial. There might be a way to fully remove the air shroud and the plastic cage attached to the motherboard and replace the heatsinks with some Noctua heatsinks but I have not tried this. I need to carefully measure the height of the heatsinks to see if they can fit. 

You can find the Dell 5pin to 4pin on Ebay. But caution... my Dell T5820 motherboard have 5 and 4 pin connectors and THE TWO (4 and 5 pin) connectors on Dell Motherboard have the plug sequence changed if compared to standard pins. How i found only 5 pin to 4 pin adapters on ebay, and my motherboard have some 4pins plugs, i take my 4 pin fans from the original Dell fan and i removed this plug and i switched the ebay adapter plug 5pin by this one, replacing then by a Dell 4 pin connector (Dell 5 pin and 4pin have the same sequence, the difference in 5pin is one plug havent connector, is in blank). But this change is only to the 5pin plug from adapter! You can not modify the another plug (4 pin standard) in the adapter cable. It works ony to dell 4pin fan connector. In the 5pin s connector the adapter wont need be modified (because the adapter is 5 to 4 pins and you wont find 4pin dell adapter to 4 pin standard).

After this, i connected the Noctua fans in the adapters and they are working fine.

Hi there,

Just wanted to let you know that our internal team is still working on this one.

We'll get back as soon as we have an udpate. 

This is an old thread, but an important one.  This has been an issue for years and I have a Dell Precision 7920 that was built around 12/2022 and am testing it as I am responding to this thread using prime95.  At this time, CPU0 = 66degC and CPU1= 86degC.

What is your solution for solving this issue?

It seems that the only working solution is using fans to remove the heat.  Has Dell come up with a solution?

Thanks.

George

Hi - Still waiting on an update on this. I'm seeing very high temps under load.