Why is GPU2 so much hotter than GPU1?

[Yannick]

Hi all,

My computer is mining very well and stable.

However, because I want to keep the temps of my GPU's (2x5870) below 80°c, I can't clock my GPU2 to get a result of over 400 Mhash/sec.
GPU1 is no problem to overclock with temperatures staying well below 80°c.

My current settings:

GPU1:

Core: 995
Mem: 390
Hash/sec: 420
Fan speed: 91%
Temp: 74°c


GPU2:

Core: 900
Mem: 337
Hash/sec: 393
Fan speed: 97%
Temp: 80°c


As you can see, it's impossible to overclock GPU2 like GPU1 because it gets over 80°c.

Here is a picture of my rig:

http://i52.tinypic.com/2w2mqyt.jpg

The GPU above is GPU2. What surprises me is that this GPU has the most free space around it.

The GPU below is GPU1 and is very close to my PSU.

Has this something to do with my setup? Or is my GPU2 damaged? :-(

[deepceleron]

Heat rises.

[Yannick]

Heat rises.

Haha, I forgot that. Didn't know it had so much impact on a GPU above another GPU with so much open space between them.

As you can see on the left of my picture, I placed two additional GPU fans to blow away some hot air. Doesn't help.

I suppose I have to blow air directly on GPU2?

[2weiX]

I have the same problem:

I have three 6950s and one 5770.

When I put the three 6950s in one case, one specific card ALWAYS gets hotter than the other two, no matter what slot I put it into.
If I, however, put that card into another rig with the 5770, it keeps well chilled.

strange, eh?

I run them at 850core / 300mem, fan @ 100%

[deepceleron]

Some cards just run hot, something about the variance in the silicon chip manufacturing (just like how some overclock better than others). If you switch the cards and the hot card is still is the same card, it's probably a manufacturing difference.

You can put a fan in the case blowing straight down between the cards (or even better, a big fan in the side of your case blowing on the cards), and that will alleviate some of the heat transfer from the lower card, and also help with the restricted airflow that the upper card has.

[drsnuggles]

It could be the location of the temp sensor and the precision of the sensor that could cause what you see.

[Rob P.]

Could also be that the card has a bad TIM.

Take the heatsinks off and reapply TIM on the "hot" card and see if it helps.

[bmgjet]

Replace thermal compound and lap the heatsink. Not all of them are made to the same standard and being mass produced you can easly improve on there distribution of thermal compound.

[Drath]

I had the same issue you do. My setup is the same. What helped me was installing a fan to the side panel drawing in air. and a fan at the top of the case pulling the heat out. Now both GPU's run at the same temp. Also you only need 1 of the cross fire jumpers on your cards. Hope this helps.

[dmcurser]

artic silver is a good compound better then most oem stuff would recommend that

[Yannick]

I had the same issue you do. My setup is the same. What helped me was installing a fan to the side panel drawing in air. and a fan at the top of the case pulling the heat out. Now both GPU's run at the same temp. Also you only need 1 of the cross fire jumpers on your cards. Hope this helps.

I have the Thermaltake Element S case (http://www.techpowerup.com/reviews/Thermaltake/Element_S/)

With a huge fan in the side panel and a fan in the top to blow out the air and I placed two additional fans in the back at the GPU's to such out the hot air, but believe it or not, if I close my case with the rear fan sucking air into the case, temps raise from 79 to 85° !!! If I just remove that panel with the fan, temp stays at 79°.. I suppose the fan just blows all the hot air through the case. Not sure why this huge fan isn't very helpful.

[JoelKatz]

artic silver is a good compound better then most oem stuff would recommend that

If you are going to use Arctic Silver, make sure to get AS5 -- it's not conductive, is much more forgiving of mistakes in application, and cools about 2C better than AS3. AS5 typically performs about 4C better than other high-end thermal interface materials.

One caution: Arctic Silver is not designed to fill gaps. If your graphics card uses gaps between some of the chips and the heat sink (often filled with a spongy or foam like material) do not remove the sponge or foam. Just leave those parts alone.

[joulesbeef]

have you not tried to swap them and see if you have the same problem?

also try swapping the power connectors, if it has trouble drawing power for what ever reason it might get hot.

this on top of what everyone else is saying but I wouldnt go opening it up and putting on artic silver until you made sure it was actually a problem

[Dargo]

Here is another suggestion. I had a similar problem with a similar card (mine is a Sapphire 5850, and from the photo it looks like you have Sapphires). I installed a Lian Li External PCI cooler over my upper card, and it now runs cooler than the lower card. It has a 140mm fan pulling hot air straight out from the card. The cooler is about $38 from frozenpcu.com (maybe more than you want to spend, but it worked great for me). Two caveats about this solution are 1) it completely covers the video ports on the card (I just use the ports on the lower card), and 2) it is actually designed to mount over empty expansion slots, not over occupied slots -- it still installed OK, but I had to unseat the card and push it back a bit to get the cooler on (once the cooler is on you can put the card back in the PCIe slot), and I now only have one screw holding the card to the expansion slot. So it was a slight kluge, but really works.