Hi everyone, can somebody please explain me how can I solve this without having to buy new stuff.  I'm running a Z87 FTW (1.11 Bios), 4790K (stock), 32GB, 02 GTX 660 FTW 2GB w/ACX and W7 x64.  Everything is working, but I've just realized that one of the 660 is running considerably hotter than the other one under load (15-20C more than the cooler one).  I'm running SLI (@ 8x according to CPU-Z) on slots 1 and 2 (as shown in the pic) and I'm guessing they're just too close together to let the one in slot 1 cool properly.  I tried running them on slots 1 and 3 but SLI didn't work.  I've been reading the manual and found out this, however don't know exactly what it means "Z87 FTW: 1x16, 2x8, 1x8+2x4, 1x8+4+4+1" (page 21).  So the question is what other options for running SLI do I have if I want to give both 660s some spacing for cooling.  Can somebody just please tell me what slots should I use?? Will 1 and 4 or 2 and 4 work @ 8x? (I'm guessing trying a accomplish 16x is out of the question?? .  Thanks for any help.

Welcome to the forums.
 
Using the 1st and 2nd PCIe x16 slots seems to be your only option..Slots 1 and 2 run in x8 Mode when they are populated..The other PCIe x16 slots are x4 Mode slots.
 
NVIDIA SLI requires that the PCIe x16 slots run in x8 Mode or higher.
 
But, you may try the latest version of a tool called DifferentSLIAuto that hacks the graphics driver to run SLI in modes lower than x8, but no guarantees..I would try it and see how it works for you by possibly allowing you to run one card in the 3rd (x4 Mode) PCIe x16 slot..The instructions are in the download package.
 
There is some info about your mobo and the PCIe lane distribution in a review here.
 
When uninstalling the graphics driver, use a utility called Display Driver Uninstaller (DDU) to remove the driver and it's leftovers.
 
Running a benchmark such as those from Unigine (which are very popular benchmarks in the gaming/enthusiast community) to compare before and after performance would be good to do..If DifferentSLIAuto works for you, you'll likely take a hit in performance but it may not be anything major to worry about or even noticable when gaming.

bob16314
Welcome to the forums.
 
Using the 1st and 2nd PCIe x16 slots seems to be your only option..Slots 1 and 2 run in x8 Mode when they are populated..The other PCIe x16 slots are x4 Mode slots.
 
NVIDIA SLI requires that the PCIe x16 slots run in x8 Mode or higher.
 
But, you may try the latest version of a tool called that hacks the graphics driver to run SLI in modes lower than x8, but no guarantees..I would try it and see how it works for you by possibly allowing you to run one card in the 3rd (x4 Mode) PCIe x16 slot..The instructions are in the download package.
 
There is some info about your mobo and the PCIe lane distribution in a review .
 
When uninstalling the graphics driver, use a utility called (DDU) to remove the driver and it's leftovers.
 
Running a benchmark such as those from (which are very popular benchmarks in the gaming/enthusiast community) to compare before and after performance would be good to do..If DifferentSLIAuto works for you, you'll likely take a hit in performance but it may not be anything major to worry about or even noticable when gaming.

First things first, thank you for the welcome and the reply and the tips.  I'm out of town right now, will be back in a couple of days to try DifferentSLIAuto, but first will run a test with one of the Unigine benchmarks to compare to the afterward results.  Before leaving I was testing the GPUs with EVGA's OC Scanner X and monitoring temperatures with EVGA's PrecisionX.  Even though still a 20 degrees difference I got to reduce the temps a little, hitting 52 and 71 degrees on them (full load), now I don't really know if this is good or not but it's better than 60-80 than I was getting before.  Got this by tweaking the fan curves in PrecisionX.
 

Cool GTX
 
Not sure what case and fans you have ? Case and number and size of fans, do they blow In or Out ?
 
It is Normal for the top GPU to run warmer in SLI.  Your zero space MB makes this even more pronounced
 
You need to get the heat out of the PC case as ACX does dump most of the heat out of the side of the GPU into the case
 
Easy test:
 
Set all case fans @ 100% and test temps
Now remove side panel from PC that covers the GPUs .... temps go down ?

Thanks for the reply.  I'm running a Cooler Master Haf X, front and side 20mm (intake), 02 top 20mm + 01 back 140mm (exhaust).  CPU is under a Arctic Liquid Freezer 240 in a push config against the top of the case (both 20s are pulling air).  Also have the GPU bracket pushing air to the GPUs with a 120mm fan. PSU is a Kingwin 1000W.  So far all fans except for the top ones are at max, top ones (including the AIO unit) are being regulated by CPU temp.  Funny thing is the only fans I can hear are the 4 fans from the GPUs.  With this config is that I'm getting the mentioned results.

Little update ...
  Been working on OC'ing the CPU so haven't really given the GPUs a little time.  Will update as soon as I'm done with the CPU (so far 4.8Ghz at 1.269V stable)