I think the "temp" is the CPU.
118F is about 48C which is not too hot, it shouldnt shut down your computer. But, how do you know this is the actual temp of the graphics card. You mention you have a temp reading on the front of your computer, do you know exactly what it is measuring? Because if speedfan says your CPU is 40C, this is much lower than 48C (118F). Just trying to figure out where that 118F is coming from.
A 2.8G CPU should not be overheating on Civ. When you mention your graphics card is custom made, what do you mean?