When stopping for gas or a meal after 2-3 hours of steady driving on the freeway, my 1990 Volvo 760 Turbo fails to restart. Generally after a 20-30 minute wait, with the hood open, the engine finally restarts as though nothing had happened. I suspect an overheated part , perhaps a capacitor in the ignition system. Has anyone had experience with this problem? I would like guidance on what part has to be replaced. My trusted mechanic has been unable to find the culprit because, of course, the engine is never overheated when the car is in his shop.

In what way does it not start? Does it turn over at all? Was it overheating while running before?

Sounds to me like heat soak. The intercooler just gets clogged with hot air. You could open the hood if you are gonna just be a couple of minutes to allow it to cool down. If you are handy, you could get some nozzles and blow CO2 across it to cool it down really fast. <img border="0" src= smileys/smiley4.gif>

to help cool your intercooler try to remove whatever obstructions there are keeping cold air from flowing accross it. If needed be make some ducts