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On Sun, 16 Jun 2013 22:12:33 -0400, "Eisboch" wrote:

This is pretty simple but I can't figure out what I am doing wrong:

Bought a 2002 Saturn for a kick around town car. It's a Canadian
car, so the odometer reads in kilometers instead of miles. It's a
very basic car and you can't set it to read in miles.

So, the day I picked it up it had a quarter of a tank of gas. I
stopped at the gas station and put in $20 worth. At $3.68/gal that
amounts to about 5.4 gallons. It brought the gauge up to about 3/4
full.

Drove the car around for over a week until the gauge read a quarter
tank again. According to the odometer, I had travelled 700
kilometers.

1 kilometer equals 0.62 miles. So, 700 kilometers time 0.62 equals
434 miles.

Divide 434 miles by the 5.4 gallons I had burned and it says the car
is getting about 80 miles per gallon !!!

I was just trying to get a rough idea of what kind of mileage it
gets,
but this can't be right. What am I doing wrong? I feel like an
idiot.

=====

Most odometers are reasonably accurate and your conversion
calculations are correct so the issue is likely to be with the fuel
measurement. The best way to calculate mpg is between fill ups since
that takes the gas gauge out of the equation. With a small tank
you'll probably need to take the average of several different fill ups
to get an accurate number.

--------------------------------------------

The gas gauge was my first thought but after thinking about it,
there's no way I could have driven 700 km or 434 miles in the time
frame discussed. A rough estimate of my trips came up with maybe 150
miles tops. That would equate to about 27 mpg, which is a lot more
realistic than 80 mpg.

So, this morning I started googling Saturn odometer issues. Turns out
it's a known issue, not only for Saturns, but for many cars made by
GM.
In the old days the speedometer and odometer were purely mechanical
with a cable turning through gears, usually from the transmission to
the instrument panel. No more. Now it's all done electronically
through a chip called the "Body Sensor Module". Saturns in
particular have quite a history of problems with it. The speedometer
reads correctly but the accumulated miles (or kilometers) can be way
off. To make matters worse, you can't simply replace the module. It
has to be uniquely programmed specifically to the car's VIN number. If
not, an error appears that records a fraudulent mileage reading. This
is to prevent "roll backs" of the odometer by shady dealers. Good
grief. Technology has taken all the fun out of cars.

I'll confirm this today with either a GPS or I'll drive my truck a few
miles down the street and record the distance driven. Then I'll do
the same trip with the Saturn and compare the odometer readings. I
suspect the Saturn will register more than twice the distance.

If that's the case, I really don't care. I am more interested in
making sure the speedometer and gas gauge are accurate. So far, the
speedometer appears to be working fine. I bought the car for $2,500
just for local driving. The odometer read 191,083 kilometers which
converts to about 118,000 miles. If the module has been bad for
quite a while, the actual mileage may be much less. That sorta makes
sense because the car is in excellent condition .... almost looks new
..... and runs and drives like a car with much lower mileage.