Not if the engine is just used for a brief period of time and then shut down. A diesel engine would also add to the already big price tag. It would be great if you were running long stretches of highway like a train but then why not just have a straight diesel engine? Trains run at a steady speed for a long time. A car starts and stops rapidly and the way the Volt is set up, I'll bet many people would use the engine for just a few minutes before getting home. The diesel engine would never even warm up.