re. factory instrumentation accuracy & mpg

Phil and Judy Rose pjrose at
Mon Jan 27 10:07:34 EST 2003

At 4:53 PM -0600 1/26/03, Chander Balakrishnan wrote:
>I have a 87 5ktq with the 1.8 bar SJM modification, and a 1990 200 avant
>stock.  The best mileage I have gotten with either car with my daily
>driving - a combination of driving around town and highway is 20 -21 mpg (as
>measured by fill ups and miles elapsed, not the computer in the car).  It
>drops a tad, to about 18-20 mpg in summer on hot days.
>Both cars have been on long trips to the East from Chicago, all Interstate
>driving, and the best they have done then is about 24-26 mpg.  These mileage
>numbers are consistent (as I remember) with the numbers on the sticker on
>the 1987 5kcsq (which I still have).  I am surprised at the 28 mpg claimed
>here.  I consider myself a normal driver, neither heavy footed or very light
>footed.  IS there something wrong with my cars or my driving style ?

No. I wouldn't get too concerned with the difference between 26 and
28 MPG. IMO, there may be very little true difference between those
numbers within the probable (combined) measurement errors. That said,
I have on numerous occasions verified the accuracy of my on-board
computer gas mileage and found it to be consistently within  5 % of
actual (usually reads a bit high--always within 1 MPG). On one
occasion last year I was able to maintain a 30-31 MPG average over a
100-mile stretch of NYS Thruway between Rochester and Utica (at 70+
mph.) That section of highway is quite level (gain/loss in overall
altitude probably less than 200 feet) although generally there would
generally be some wind at your back going in that direction. I've
always hesitated to mention the 30 MPG figure, but I'm quite
confident that "28" is realistic. I wouldn't be surprised that if I
were driving a longer distance, over more-varied terrain, the same
car would likely average something closer to 25/26 MPG.

But when I say "steady throttle", it's hard to exaggerate how steady
it has to be to avoid losing about 2 or even 3 MPG. In my experience
if I drive "normally" (meaning not paying attention to economy but
not being heavy footed either) I'll get 25-26. When I make an effort
to be a "steady Eddie", it goes to 28+. Don't laugh, but I think I
can do better than the cruise control (except the cruise control has
much more "self control" than I do) ;-)

Aside from wind and terrain, tire pressure--and  type--can be very
significant factors. What's that expression? "YMMV"
*  Phil & Judy Rose           Rochester, NY  *
*        mailto:pjrose at       *

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