Unexplained Sli temperature difference

[MagR]

Hi

I'm running two gtx 570's in sli. Case is a Silverstone Fortress with motherboard orientated so graphics cards hang down vertically. Motherboard is Asus P8P67 Pro which leaves over one inch gap between graphics cards. Both cards idle around 38 degrees. If I run both in sli the first gets to 75 degrees under 100% load and the second 65 degrees (using Unigine Heaven 2.5 benchmark for stress testing) . If I turn off sli and run just the first card at 100% load it runs at 65 degrees. What I cannot understand is why the first cards heats up by an additional 10 degrees in sli when the gap to the second card and hence the airflow to the fans is the same whether it is running or idling.

Can anyone suggest anything that explains this? I've used MSI Afterburner and GPU-Z and recorded identical temperatures. The cards are identical and give the same temperatures if swapped over.

Thanks in advance

Regards

Mag

Specs:

Intel Core i5 2500k processor overclocked to 4.6Ghz
Asus P8P67 Pro motherboard
8GB Corsair Vengeance LP 1600 Mhz memory
2 x Palit Sonic GTX 570 in sli
Crucial C300 256GB SSD
WD Velociraptor 300GB
Enermax Revolution 85+ 1.25KW PSU
Asus Xonar DX sound card
Silverstone Fortress FT-02 case

[Hoonigan]

When you're stress testing them, are both cards under the same stress? Are both cards running at 100%?

[GoNz0]

the 1st card has to work harder taking the info from card 2 so its quite normal.

[scaryjim]

Also when both cards are working .. and I know this will shock you ... the second cards heats up

OK, sorry, that was a little sarcastic, but think about it. The air used to cool the first graphics card is heated up by the second one. So when you only use one card, the second card sits idle at around 40C and doesn't really heat up the air around it that much. But when you're running SLI, the second card hits about 65C, so it'll heat up the air around it a lot more. That means the first card is trying to cool itself with hot air, which simply isn't as effective.

[MagR]

When you're stress testing them, are both cards under the same stress? Are both cards running at 100%?

Thanks for replying so promptly. Yes both cards are at 100% per the gpu usage monitor in MSI Afterburner. Heaven 2.5 is a dx11 benchmark with heavy tesselation etc which claims to have perfect sli scaling so both can run flat out without vsync.

Regards

Mag

[MagR]

the 1st card has to work harder taking the info from card 2 so its quite normal.

Thanks for replying so promptly. This makes some sense to me as I've seen similar suggestions in other posts. However I have tried connecting the monitor to the second card to see if made a difference but the temperature difference was the same. However swapping the DVI cable might be irrelevant if the first slot is still treated as the primary slot by the bios. I cannot see an option to change the nomination of the primary slot in the bios like I've seen in some boards. What is really confusing me is that there was only a small temperature difference between cards on my old LGA 1366 system with the same cards and spacing. If memory serves me correctly the second card now seems to be running cooler than before.

[MagR]

Also when both cards are working .. and I know this will shock you ... the second cards heats up

OK, sorry, that was a little sarcastic, but think about it. The air used to cool the first graphics card is heated up by the second one. So when you only use one card, the second card sits idle at around 40C and doesn't really heat up the air around it that much. But when you're running SLI, the second card hits about 65C, so it'll heat up the air around it a lot more. That means the first card is trying to cool itself with hot air, which simply isn't as effective.

Thanks for replying so promptly. I must apologise for being a little dozy - I did not in fact realise the second card would heat up the air around it. The Palit Sonic design uses a two fan design with a large sleeve so most of the hot air is supposed to be exhausted out of the back of the case (in my case top) through the back plate of the card. To test your idea I ran Heaven and when everything was nice and hot I removed the side panel and put my hand in the gap between the cards (after making sure I had discharged all static).

The air to the bottom fan of the first card was pretty cool but that going to the upper fan was much warmer. With the second card the air to both was nice and cool. I then tried to find out where this extra heat was coming from and as far as I can tell it is coming off the back of the circuit board of the second card - all the little electrical circuits seem to get quite hot. This is heating up the air in the gap between the cards which is being sucked into the first card mainly by its upper fan.

I'm now wondering if there is anything I can do to reduce this. Perhaps it might be possible to put a sleeve at the back of the circuit board of the second card so its heat is not drawn in by the first card. A piece of cardboard might do! Alternatively it might be possible to rig an extra fan to the cards to blow air straight into the gap.

Any suggestions would be appreciated and thanks again for your help

Regards

Mag

[GoNz0]

your well under max temps and i doubt any game would punish the cards like a benchmark, leave it be and you will be fine m8.

[Hoonigan]

If you really feel you need extra cooling, this might be useful http://store.antec.com/Product/cooli...5-75018-9.aspx

[scaryjim]

Hoonigan's probably got the best option there - also remove the PCI slot cover between the cards: that'll give the warm air somewhere to escape from! Basically you just need to get some kind of airflow between the cards to move the warm air away a bit and stop it being sucked into the cooler for the first card.

[Pob255]

My guess is it's a combo of GoNz0 and scaryjim, one thing you have to remember is that the back of a card can get rather hot, the heat travels into the the copper that's in the pcb and heat radiates in all directions not just one, the heat from the back of the 2nd card heats up the air that then get drawn into the first card which reduces the cooling efficiency.
At the same time it could well be under slightly heavier load if it's also the controller card.

A couple of things to try
Increase the speed of the fan directly below the graphics cards.
Replace the fan with the air penetrator version http://www.scan.co.uk/products/180mm...an-700-1200rpm the air penetrator version has a more narrow focused air cone that carries a longer distance so you'd get more focused air flow over the cards.
Use some software to increase the fan speed on the first card, Palit's tweaking tool is called Vtune
Get a zalman Fan bracket http://www.zalman.com/eng/product/Pr...ad.asp?idx=225 this connects to the pci brackets on the inside and will let you position a fan directly beside the cards to help blow air over them and break up any air pockets.
eg

[MagR]

Thanks for replying everyone.

I've returned the P8P67 Pro for a Maximus IV Extreme (got a good price!). This allows me to insert the graphics cards with an extra empty slot between (there are two uncovered empty slots now). This seems to make all the difference - the hot air coming off the back of card 2 has enough space to exhaust out the top of the case without being drawn in by card 1's fans. Both cards are running at the same temperatures and neither exceeds 70 degrees in any benchmark I've run so far.

I've done a bit more research and one view on sli cards is that the reference style cards are the best for heat dissipation. These are more fully enclosed on the back so do not send much heat back into the case. Cards with aftermarket coolers are cooler when used singly but the way they dissipate heat can cause the problems I've been experiencing in sli mode. In future I'll bear this in mind when chosing cards to sli.

Thanks again

Mag

[pooley]

I have two reference gtx470's in sli in a Sliverstone Fortress case and like you the top card gets around 10 degrees hotter than the bottom card.

As been already mentioned the top card will be taking in warm air from the bottom card, as long they are within safe temps I don't see it as I a major issue.