Which GPU do you have? The CPU cooler's main job is to keep the CPU cool, not exhaust hot air. If you have a blower-style fan on your GPU, your CPU cooler is taking in that hot air from your GPU.
Have it pointing toward the rear so that it takes in fresh air from the front of the case.
Does the 912 have removable HDD cages? If so, remove a unused HDD cage so that the air flow can go directly to the GPU and CPU.