[baloo]

I'm asking because there isn't a whole lot you can do to a diesel to drop its mileage. Cold starts, idling, driving at very low speeds, driving at very high speeds, there's virtually no scenario where diesels start guzzling.

This is in stark contrast to gas engines which are pretty inefficient at idle/low speeds because of pumping losses (throttle), inefficient at very high speeds because they run very rich at wide open throttle and they also suffer at low temps because they run rich and have to disable deceleration fuel cut.