Re: Lifespan of ford e-350 shuttle bus + advice
The conventional wisdom is that the Ford 7.3L diesel has a 300,000 MILE service life, but a well maintained motor can go far past that. The bolt-ons, including the tranny, of course need replacement sooner. Your 300,000K engines still have a lot of life left in them.
As far as gas mileage goes, 10 - 15 is about as good as it gets.