Replacing gpu fan

[chicken665]

I have a VTX 6950 2gb gpu and the stock fans were quite loud and made a clicking noise, so after searching around online i saw that i could remove the shroud and fans and attach 2 120mm case fans. So I got 2 noctua nf-f12s a y splitter and a fan to mini gpu connector.

 

It turns out the standard 4 pin pwm to mini 4 pin gpu adapter wouldnt fit as the gpu needed a 3 pin connector with only 2 pins on the board itself. Luckily I manafed to find a cable that does what I need:

 

http://www.maplin.co.uk/p/graphics-card-3-pin-to-vga-fan-004m-adapter-a38gf

 

It did mean that I wouldnt be able to check the rpm and have pwm control, but the fan speed would be set through the gpu as is the case with the stock fans,

 

I connected everything up and the result was much quieter than before, although my problem now is the temps, it went from 37c idle/70c load with the stock cooler to 40c idle/92 load and in gpu-z it looks like the vrm temps can get above 113c. I've since removed the two fans and put the stock cooler back on since I thought it could be that the thermal paste wasnt applied well or I needed to replace the thermal pad covering the vrm.

 

But with the stock cooler I get the old temps 37c idle /70c load. There are some things to note, when the 120mm fans are attached the heatsink only covers around half the height of the fans - so is half of the rated airflow for the fans lost? Also when attached the fans do not directly sit on the heatsink and so theres a gap between the fans and the heatsink as the fans sit on the raised parts on either side like this picture:

 

http://www.ixbt.com/video3/images/any-6/powercolor-6950-cooler1.jpg

 

considering the max rpm of the noctuas is 1500 and the stock fans could be 3000 is this the reason, or is it the air leaking from the sides? What could I do to properly cool the cards with the noctuas since they are much much quieter? I will update this post with more pictures of my setup when I can.

[Sauron]

The reason is all the things you listed: the fans aren't making contact, there is air leak, the heatsink and fans don't match in size, and the rpm is lower. It was a very bad idea to change the cooler with two 120mm fans. It can work sometimes, but only if the fans are touching the heatsink directly and there is as little air leak as possible. There is no way that I know of that would allow those fans to be as efficient as the stock cooler, however you could try getting the industrialppc 3000rpm version and see if something changes, but it would still be a better idea to keep the original cooler. Of course you could get a waterblock, but it would be expensive and hard to setup.