Maximum CPU Temperature for Core 2 Duo E6400

"61.4 degrees centigrade. Of course, this leaves zero margin for safety, and your motherboard may or may not record temps in half-degree increments. So I'd stick with 60 as a nice round number that happens to give you about 1.5-2 degrees of wiggle room. This would be the maximum upper limit of what your CPU would handle, you'll be pushing the envelope of its design.

If you plan on keeping this overclocked forever and a day, I'd even consider something lower, so that the safety factor involved is larger, say 55 degrees.

And of course, this advice is given with the standard disclaimer that if you cook it by overclocking it, it was your decision, not mine; I'm not responsible for what you do; and you get to keep the burnt bits and pieces."