[Christ]

Diesels have such a low redline b/c of weight and other factors, but weight plays a major role in keeping engines running as well. A diesel engine tuned properly could idle as low as 50-75 RPM (So can 225 slant six gassers, but you'll smear the bearings.) With a properly designed oil pump that could function at a speed that slow, you'd almost never notice the fuel consumption from idling a few minutes anyway. Not to mention that under 0 load, idling, the diesel runs so insanely far from stoich that it's uncounted anyway. They literally use *just* enough fuel to keep running, and they use very little to maintain 1000 RPM or so... imagine 50RPM.

NVH is the real problem here.. you'd have to seriously balance a diesel to keep it from wiggling your eyeballs out of your head at that low engine speed.

Theory behind keeping a diesel running: They like to be hot. Hot. HOT. Hotter - better for fuel combustion, less energy necessary to heat up the air enough to combust the fuel = more efficient. That's all. It's not that you can't stop and start them, it's just that they're less efficient the cooler the motor is. Same with gassers, but more pronounced and obvious. That said, once they heat up, they don't lose that heat very quickly. Remember, most diesels are basically cast iron bricks. Sure, you'll lose a bit of efficiency each time the engine starts, for a few seconds, but you're only using it to accelerate anyway. Under load, it will heat back up very quickly. I'm sure they could insulate the engine as well, making it keep heat longer.

I still like the 50-75 RPM idling idea, though.