Incidentally, I got 50 mpg twenty years ago with a Nissan Sentra Diesel.
Then why not a diesel hybrid?
Yeah, I got in the 40s with an old 89 civic hatch, 87 unleaded gas. I get 30 plus in my 02 protege 5, and 30 in a 91 prizm. Not too far from the hybrids really, without the battery/power issues. I use synthentic oil in the cars, use torque and momentum rather than overshifting, and throw in a bottle of lucas fuel additive once every 4 or 5 fillups.