Overheating While Idling on Inclines, What would cause this? Options

[Coomer]

I was in a parking garage shooting some photos today, and as I was parked on an incline (front up, rear down) taking some pictures I noticed something dripping from the car. I immediately shut the car off and noticed that the temperature needle was higher than normal, like this: (sorry for the bad photoshop)



Once I shut the car off, I popped the hood, and the fluid was actually coolant that had come out of the top of the reservoir somehow...fluid was within the min and max levels though, like it always is.

I let the car cool off for a while while I adventured off to take more pictures and came back and had no problems whatsoever, even sitting at idle for a long period of time (on a flat surface.)

So I found another incline, and this time parked with the front down and the back up, let the car idle for a few minutes, and sure enough, the temperature gauge started rising again past normal levels, this time with no fluid coming out of the reservoir though. Again, I shut off the car and let it cool down, and now it's fine again. It's really hot outside, but only when I leave it idling on an incline does the water temperature rise. It's fine at idle on a flat surface, and while driving (both up and down steep hills at 3,600 RPM...I make the very hilly drive to Yakima often.)

I couldn't think of what would cause this...I bled my coolant system a few thousand miles ago (probably like 9-10,000 miles.) Anyone have any ideas?

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