LucaMauri,
The brief answer to your query is that the Quadro 4000 is itself a very hot running graphics card. I've had two of them and during one long rendering session, the tempertature reached 102C- the card limit. Some ideas to solve the problem:
1. First, try pepping up the z800 fans a bit. if the z800 has a "Thermal" setting in BIOS that lets you advance the fan idle speed, change that up a few asterisks. I did that today on a z620 and the CPU temeratures that were 43-44C are now 37-38C.
2. If that is not sufficient, there were a couple of alternative cooling solutions, one was a an expensive water block- $150 or so, and the other- still available at $60-$70 new is the Gelid "Icy Vision" specifically for the Quadro 4000, though I think it fits whatever the GTX version of the 4000 was at the time also.
3. The problem with the Quadro 4000 was that it is a single height card and a large volume of air can't be easily pushed out the back. These days, instead of spending $65 on a Quadro 4000 cooler, consider selling the Quadro 4000, which are still desirable, and adding the sales value to the cooler and buying a Quadro 5000 (2.5GB) which does use a bit more power, but is a double height card, cooler and cosequently cooler running. The performance of the 5000 is noticeably better as well. On Passmark , the average 3D mark for the Quadro 4000 is 1935 and the for the Quadro 5000- 2710.
4. If your budget is flexible there are two very good values for Quadros: A. , the excellent K620 (2GB) Passmark = 2276 and uses very littel power, producing very litle heat. These are $160 or so new or used for $90-$100. and B. The new Quadro M2000 (4GB)- $430 or so and Passmark = 4443, very similar to a Quadro K4200 - with 4434 but that cost $830 new and not that long ago. It also uses so little power it runs off the PCIe slot alone. That's relativel;y expensive, but would be suitable for professional use for longer than the other options and be transferrred to the next system.
I have a Quadro K2200 in the z620 which is an analysis / simulation / renderin/g system, but that may well become a M2000 in a the Spring. and the K2200 can go to the second z420, which is for graphic design. The K2200 has one the higher 2D performances for recent Quadros.
Probably early-mid next yearthere is also going to be a new line of Pascal Quadros- the top end ones P5000 and P6000 are announced and that series is going to be astroundingly good. The "P4000" - conjectural name- situated below the P5000 if true to form ( based on GTX 1060- might be close to K6000 level.
Power Usage:
Quadro 4000: 142 W
Quadro 5000 : 152 W
Quadro K620 : 45 W
Quadro K4200: 108 W
Quadro M2000: 75 W
Cheers,
BambiBoomZ
z420 > Xeon E5- 1660 v2 / 32GB / Quadro K4200 / Samsung SM951 (256GB) + Intel 730 (480GB) + WD Black 1TB / Windows 7 Professional 64-bit > 2X Dell Ultrasharp U2715H
z620 > 2 X E5-2690 / 64GB / Quadro K2200 / HP Z Turbo Drive (256GB) + Seagate Constellation ES.3 1TB / Windows 7 Professional 64-bit > HP 2711x
z420> Xeon E5-1920 / 24GB / Quadro 4000 / Samsung 840 250GB + WD RE 1TB > Win 7 Professional 64-bit > 2X Dell 24"