e8400 weird temperatures

So I've read about all the problems with the e8400's temperature sensors etc. But it seems to be worse in my case. I'm running an e8400 with a stock cooler, the case is open and there's one additional fan in the back. The temperature in realtemp when idle is 62C.

When I run the blend test in prime95 it starts getting creepy, as the temp quickly shoots up to 100+. That's when I stop the test. When I feel the heatsink with my hand it's quite cool. About as cool as my hard drive at idle, which is 41C.

What's the deal here? Are the sensors lying? Or should I be afraid of frying the CPU? Is it possible that the cooler is poorly attached or there's not enough thermal paste? There was some already on the cooler so I figured I don't need to put more. I had a bit of a problem attaching the cooler at first as it didn't stay in place. Now it seems to be correctly in place, but I'm not sure...

Also, I updated the BIOS just before I tested with prime95. I remember getting lower idle temperatures by about 10C before updating it. Could that have caused the problem?

Another interesting fact: when I run MSI's Dual Core Center, it tells me the temp is 51C. Motherboard is MSI P43 NEO.

Thanks, even though I solved the problem already.

It was what me and you suspected, the heatsink was poorly attached. It has these retarded plastic things which I was afraid to push hard enough for them to go through properly. So the cooler was attached enough not to fall off, but not enough to cool normally. A lesson for newbies. This is the first PC I've ever assembled from parts.

Temperatures are now normal for a stock cooler and low-end case, I guess. Running prime95 for about ten minutes at 60C.

I didn't apply new thermal paste before putting the cooler back again, though. I don't have any and it's saturday evening. Is that a bad idea, should I wait till monday and get some paste?