Jim Cathey wrote:
Jim has mentioned he doesn't frequently drive the Frankenheap on the
highway, so his good mileage makes sense.
That is true, but the best mileage has been on tanks that included
more freeway driving.
That makes sense. Nothing kills mileage like having to start and stop a
lot, especially on an automatic transmission car where you have a lot of
slip at low speeds. The heavier the car, the more dramatic this can
be. My '90 Ford Econoline would get 16 mpg highway, but more like 10
mpg in town.
In most cars I've had, the best fuel economy was during long excursions
on rural roads, where I rarely had to stop but also rarely got above 60
mph. Driving a steady 55 on 2-lane highways in my Honda Civic Si, I
once got 40 mpg for two consecutive tanks, a 10% improvement over my
usual mileage in that car. This was done in 5th gear, running low in
the RPM range with relatively wide throttle openings, which is the best
scenario for fuel economy in a gasoline-engined car. (This may sound
counter-intuitive, but the farther the throttle is open, the lower the
pumping losses. You have to stay away from wide-open throttle, though,
because many fuel-injected cars shift from a "best economy" mixture to a
richer "best power" mixture at that point.)
Oddly, the fuel economy of my 300D Turbo rarely strays much from 28
mpg. The other diesel I've owned, a Vanagon, was the same way -- it
would dependably get 26 mpg, with very little variation. Maybe the lack
of a throttle plate in diesels means they're less sensitive to driving
technique.
