You can be sure about this:

With certain exceptions and lucky fingers or whatever you
want to call it, most of the components, mainly high density
microchips works very marginal even at the manufacturer
specifications, if not fail before that.  Some of them
can work nicelly at the marginal stress points, and maximum
limits pointed by the manufactuer, but accelerating its
infant mortality.  You can hook up an environmental chamber
to run a chip specified as a maximum of +55¡C during 72
hours, but chances are you are reducing its end of life.

So, if you want to go to temperatures out of comercial grade, 
just don't lose time, brain, your sanity, just don't think 
twice, go to industrial grade, or in your case, automotive 
grade... perhaps military...  It is better to have delivery
and availability problems than "product" problems. 

Remember, your environmental chamber needs to simulate all
the automotive functions, even vibration, bumps, humidity,
temperature, "kids fingers, gum, candy melting on the back
seat cup holder..." :).
--------------------------------------------------------
Wagner Lipnharski - UST Research Inc. - Orlando, Florida
Forum and microcontroller web site:  http://www.ustr.net
Microcontrollers Survey:  http://www.ustr.net/tellme.htm