The Toyota D-4D engines are *very* good. I drove a 150BHP Avensis D4-D over 150 miles, at average 56mph, with air-con on for about 30 mins, and with a cold start through town at the beginning, and got 91MPG UK (=75.8MPG US). Most people driving the car other than me tend to get 45MPG (UK)
The only problem is, being modern engines, they can't run veg oil (which is practically zero emissions).