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On a 400 mi trip where I averaged 63 mph (OBC data), fuel economy was 33.7
mpg.  Cruising speed ranged from 60-80 mph, with excursions (albeit brief)
to 90-110 mph.

Suburban driving, 70% highway at 60 mph and 30% city stop-and-go, gives
27.5-28.5 mpg.

All-city driving is more like 23 mpg.

My driving is more to the conservative side, though I do try to put my foot
in it every so often.  Mileage during winter with oxygenated fuels has been
running about 8-10% lower (i.e. 2-3 mpg less).

I don't specifically know how the range data is calculated but suspect it
may be something like the following.  Speedometer signals are integrated
with fuel flow data from the fuel system to give instantaneous MPG readings
(on the analog gauge below the tach.)  I believe this is so because of the
instantaneous response of this gauge to throttle application or release.
This analog signal then is used to calculate a "current" mpg figure, which
will change depending on current driving habits- being lower if you are in
city traffic and higher on level highways or down grades (I don't know how
often this current average is calculated, but it could be once every
minute).  The "current" mpg value is then combined with the fuel gauge
reading to estimate remaining range.  I found when I left work last week
the range read 81 miles, and 15 miles later at home it had increased to 86
miles, reflecting the high mileage I was getting on the return trip, which
happened to be mostly down hill.  Subsequently I drove 30 more freeway
miles at 60 mph and the range read 76 miles, again saying that based on my
most recent driving habit/economy, I could go farther than if I was driving
as I had been on previous shorter trips.

Some other miscellaneous information.  The E-36 fuel tank is in a water
wing shape to clear the drive shaft, and because of this has two fuel gauge
sending units which have their outputs averaged together.  On a '92 that I
previously owned, these would occasionally act up electrically, giving me
readings of Full or 1/2 full at somewhat unpredictable intervals on a
freshly filled tank.  BMW alerted their dealers to this problem (it is
related to a computer glitch - not the sending units), so they are aware
and supposedly have it fixed in later cars (I haven't experienced it on my
'94).  Also, the padded dash piece on my car and many others has warped
over the central air vent, leaving an unsightly gap.  Word from the local
dealer is that BMW has redesigned the dash (those were his words, and I
suspect the truth is more reengineered this piece of it) and new
replacement parts should be available after the first of the year.


______________________________________________________________________________

  Timothy P. Burns                                  (303) 966-5929
  Los Alamos Program Office at Rocky Flats          (303) 966-4933 FAX
  Los Alamos National Laboratory                     [email protected]
  P.O. Box 4013, Bldg. T130A
  Golden, CO  80401-0013

             The opinions expressed or implied are soley my own
               and consequently do not represent anyone else.
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