Odd SLI Temps + TDP Percentages

[Liquid_Static]

So I have 2 evga gtx 670s (reference) in ski in a phantom 530 with almost ideal airflow. Both cards are on the stock bios and slightly over clocked so they hit the same frequency (1189 MHz)

Now for the confusing part, originally my top card was markedly hotter than the bottom (8C) despite a whole slot between them and PLENTY of airflow. It also had a much higher power percentage in MSI afterburner than card #2 (around 10% higher). Voltages are the same on both cards 1.175v, and the top one even drops below that to stay in its tdp.

I was suspicious that this was odd behavior, so I flipped the cards, and this time the same card was acting up (now at the bottom). Its consistently 2-3C hotter than the top card despite having MORE airflow than it. Keep in mind this is all at the same voltages and clockspeeds. Its TDP is also still higher by about the same amount, despite doing less work as the slave card. Interestingly enough this card also has an ASIC (in gpu-z) of 81% compared to the cooler card's 73%.

So, any ideas?

 

[Liquid_Static]

Anyone?

 

[Aithos]

You're overclocking, that means all bets are off for temps. I'm not an expert with SLI (my build this month will be my first time with multiple GPUs) but it seems to me that with overclocking you are playing the silicon lottery and it sounds like one of your cards has a clearly better chip.

Think of it this way: If you buy 5 i7-4770k cards why do some clock to 4.2 while others can go to 4.7? Because they all come with slightly different stock voltages which determine what the most you can overvolt safely is. But also, because they all have slightly different heat "signatures" for lack of a better word. Some chips just run cooler at the same speed/voltage. So even if you aren't overvolting that would be my guess.

Have you tried running them at stock clocks and seeing if they still do the same thing? I would guess they probably do but maybe to a lesser degree. If they aren't running into throttling issues I don't think it's anything to worry about though...

Edit: It's also possible that one just doesn't have as good of heat conductivity with it's TIM and if you were really concerned you could pull off the coolers and use your preferred thermal compound to replace the stock stuff. I personally wouldn't want to mess with it, particularly with warranty implications on two expensive cards, but that might even things up or even drop your temps a bit. The only reason I'd contemplate doing that is if I was adding a water block or something...