"Daniel J. Stern" > wrote in message
n.umich.edu...
> On Sat, 25 Jun 2005, Newbie wrote:
>
>> It may seem like a superfluous question, but what is the best way of
>> calculating what mmg yuor vehicle is getting? I have my miles reading of
>> course, and I can record how much gas I put in, but there was some gas
>> already there in the tank, and how do I know what was traveled on how
>> much gas? If you have a good system, please share!
>
> It's very simple.
>
> Fill your tank at a given station to a given point (say, the second time
> the nozzle clicks off). Reset your trip odometer or note the mileage
> reading.
>
> Drive the car. The longer you drive it, the more accurate will be your
> mileage calculation.
>
> Return to the same gas station -- use the same pump if possible. Fill the
> tank once again to the same point as before (say, the second time the
> nozzle clicks off). Note the number of litres or gallons, and the odometer
> reading.
>
> Divide the number of miles you travelled by the number of gallons you
> purchased. That is your fuel mileage (in miles per gallon) for that tank
> of fuel.
>
> OR
>
> Multiply the number of litres you bought by 100, then divide the
> result by the number of kilometres you travelled. That is your fuel
> mileage (in litres/100km) for that tank of fuel.
>

It is not necessary to return to the same gas station and the same pump to
calculate fuel mileage. Most fuel pumps are regulated by the local
government's bureau of weights and measures so my guess is that the amount
of fuel recorded as delivered to the tank should be close enough for fuel
economy calculation purposes.

Monitoring fuel mileage is more useful to see a trend, not so much
individual tanks. You will find over time, with the same driver in the same
road conditions, fuel mileage is going to be fairly consistent, within 2 or
3 mpg. If you see a gradually decreasing trend, take the car in for a
checkup.
--
Ray O
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