I have two GTX670PE's. The one listed as card one is always 5-10c hotter under load. Even if I switch them around this is the case. I used to think it had to do with airflow but it cant be since I now have a Coolermaster Haf evo case.
This is not my case but my SLI setup is the same. Plenty of space between the cards for air to flow through. Card two have the least direct airflow to its fans. So why is it not card two that gets hotter?
Does all aircooled SLI setups do this? It is not that it is an issue, I just find it curious.
Because one card is displaying everything on your screen. the other one isn't. the first card that is connected to your monitor will always run a bit hotter than the second card. not by much though. but overall. it's perfectly normal.
This is always the case with air cooled sli setups. The bottom cards pcb will warm up the air going into the top card or the bottom card's exhausted air will be partially recycled by the top card, depending on the cards cooler type, resulting in higher temperatures.
This isn't really applicable. Since in an sli setup both cards render frames, and they just alternate every outputted frame. The second card renders the image and it is put out to the monitor once that image passes over either the sli bridge or pcie bus. This doesn't have an effect on temperatures.
But there is no top or bottom card in this case. Both cards are on their side. The logo on the card is up. The PE cards have the twinfrozr cooler that blows the hot air back into the case. But since one of the front fans is facing directly at the cards, the hot air is pushed out the back of the case. The card that gets hotter is actually the one with the case fan pointing directly at its cooler.
Edit: I should probably add that I am using 3 screens. Two of them are connected to card two. And if I switch the cards around, it is the same thing. Card one always get hotter.
I'm talking about strictly on the desktop scenario. and not playing a game. playing a game is a different discussion, cause it will fluctuate. but from my experience with Crossfire/SLI the first card runs hotter than the second. despite hot hair being blown towards the second card.
Well he was one talking about under load, but even on the desktop this is for a different reason. When the second card is idle it basically turns completely off. But I think we both do agree about under gaming scenarios the first card does run hotter due to the second card letting off hot air and so on.
It just doesn't compute in this setup since there is a direct flow of air between the two cards, as per the image in OP. Both cards dump their hot air upwards in the case and its pushed out the back and pulled through the exhaust fan. I used to have a tower that sucked in air from the low end of the front and was pushed out the back at the top, right behind the cpu. The same thing happened then and there you could argue that hot air from card two was being dragged up to card one and the cpu. Since it is still happening, I think something else is going on but I don't know what.
The bottom card and top card both get good airflow but the bottoms is just less restricted and since it is a bottom card its pcb back will heat up the top cards intake air.
So blowing air directly between the hot pcb and the cooler of the two cards and out the back of the case does nothing at all? I think that sounds unlikely.
What I'm saying is that the 2nd or bottom card's pcb heating up does heat up the air going into the top or first card, causing slightly higher temperatures. The bottom or 2nd card has better air flow to its cooler and thus gains a couple degrees there.
I would be inclined to believe that explanation if I didn't observe exactly the same behaviour in a tower without direct airflow between the cards. They had exactly the same 5-10c difference between them in my old tower.
More of less the card in to "top" slot, closes to the cpu will be drawing in hotter air and doing slightly more work. SLi is not a completely balanced workload, the first card is always doing a little more work.
So a combination of doing a little more work and drawing in warmer air from both the CPU to the left and the other GPU to the right make it just a little warmer. I am aware you have a fan on them but heat is heat. even clean air from outside will be warmed slightly on it way to the GPUs. it effectively has to push the hot air in the case out of the way to supply cold air but because air mixes readily it also warm up as it is pushing the hot air out of the way.
That and then there is a small amount of friction. Latent heat in the PCB of the other card and the motherboard. The probes give a good loo at the temps but the entire card will not be uniformly that temperature. So some heat will also seep back in from other parts of even its own card.
So yeah more of less GPU 1 is in a center of the hottest and least airflowed (yes creating word now, real science!) part of the case.
Thank you!. No there's nothing wrong with it. It's not at all at worrying temperatures. But since I had the idea from before that it was due to hot airflow alone, it is nice to see an explanation that deviates somewhat from this formulaic answer and includes more components.
