Yeah, same thing happens to me a lot too. My friend has the same CPU HSF as me and his runs a good bit hotter than mine, not overclocked. It has a lot to do with the temperature inside the room that the PC is in as well as the case temperature. I need some case fans desperately; I have 0 in mine right now. Once I go back to college I think I may have to clock down some. I'm afraid that my dorm room will be way hotter than my house, causing the CPU to run much hotter than normal. That, or buy a cheap desk fan to run constantly on the motherboard with the side of my case off.
I hate un-air-conditioned dorms!
-Lasereth