OS X randomly crashes with two GTX 660s installed

[rgwoehr]

My configuration:
Motherboard: MSI Z87-GD65
CPU: Intel Core i5 4690
GPU: 2x ASUS GTX 660
RAM: 24GB Corsair Vengeance
OS: Yosemite 10.10.3
Monitors: 3x Achieva Shimian 1440p monitors

I've been having issues with my hackintosh freezing/rebooting ever since I added a second GTX 660. I've got my main monitor connected to the GPU in the first slot, and two other monitors connected to the card in the second slot. I can reproduce the crash by setting the default monitor to be one of the ones connected to the second card, and running GPUTest. I have no problems running it on the first card, but if I run it on the second one it freezes within a few minutes, or if it doesn't freeze the computer lags (even after I close GPU test) until I reboot it. Usually when it happens, the only thing I have open on the monitors connected to the second card is twitter, mail, and iTunes. I assume my screensaver causes it to crash occasionally too, because sometimes I will walk away for a few minutes and come back to find my hackintosh sitting at the login screen.

I initially thought the second graphics card was bad, but I tested both cards (individually and together) with GPUTest in my Mac Pro 5,1 and it never crashed. Also, if I switch the cards around in my hackintosh, the "bad" card works fine and the "good" card has issues. I've tested the cards with both the Nvidia web driver and the stock OS X drivers, and it doesn't seem to make a difference. I've checked the RAM and all 4 sticks are good. I threw an AMD 6450 in the second slot and ran GPUTest on that and it didn't crash (though I couldn't connect both monitors to that because it only has one DVI port, if that makes a difference). I've tried to replicate the crash in Windows as well, but it didn't crash.

Does anybody have any idea what the issue might be, or what I should check next? Any help would be appreciated.

TL;DR: OS X randomly crashes when I have both GTX 660s installed, but both cards work fine individually in both the hackintosh and in my Mac Pro.


This is what was in the console after the most recent crash:
5/24/15 8:02:00.000 PM kernel[0]: NVDA(OpenGL): Channel timeout!

 

[g-star]

I dont have a solution for you, but it sounds like I have a similar problem.
I have a "Early 2009" MacPro with a NVIDIA GeForce GTX 660 3072 MB card installed.
Im running on the OSX driver in Yosemite (10.10.3) and it works well for the most part. Machine runs certain processes a lot faster, but it crashes usually within 4 hours.
Im beginning to think it is temperature related as it seems to happen only after having worked for a while, never right away. I thought it was a power issue so I bought a separate 660W power supply that I hooked up externally, but it still crashes.
When I reinstall the original GT120 card machine is once again rock solid.
I think the issue relates to either:
1: Heat management
2: Buggy driver

When I had both cards in the machine, the crashes happened more often and a lot sooner.
Given the thickness of the GTX660, there was very little room between the two cards.

My theory is that the card overheats and shuts down, and the driver doesnt handle this situation well enough. Im also thinking Apple didn't test the driver long/hard enough to see the problem during development because it is a very limited market for this given how relatively few macs with this configuration.

 

[rgwoehr]

I ended up just removing my second card and putting my radeon 6450 in its place. It's not exactly the solution I wanted, but it seems to be working so far.