On 5/14/2016 7:32 PM, Ed Pawlowski wrote:
Where are you getting the numbers? Since you are talking a trip this morning
are you using what the car is telling you? If so, it is probably wrong.

The last five cars (different brands) had the computer that gave you the mpg of
a trip and since the last fill up. I've checked the old method of filling the
tank and calculating. The car computer ranged from 2 to 6 mpg too high

Ours has been really close. We record the odometer reading and the gallons
of fuel that the *pump* claims to have dispensed. We compare this to the total
that the car reports for each tankful along with the running average. The
car always reports *lower* MPG than we calculate.

E.g., car reports 190.3 miles on the last tank. (the car decides when it
has been "filled"; we don't "tell it"). Car claims 20.5 MPG. Simple
arithmetic suggests the actual efficiency was 21.29 MPG.

For a car that claims to get "up to" 20MPG in city driving.

Of course, if car was claiming 29 MPG for each "trip" -- then reporting an
average of 20 for the tank, we would be suspicious. OTOH, when we see it
report *5.8* MPG for a trip down the block (*a* block), we don't start
sweating!

In reality, it is very rare to really get what the official rating is. Verified
over hndreds of tanks of gas on many cars.

Perhaps you should buy a "smarter" car? :

Our vehicle currently has ~4300 miles on it. As of the last fillup (at
4259), we'd pumped 214.402 gallons into it. That's 19.86 MPG over the life
of the car.

If the manufacturer told me "up to 20 MPG" and I calculate 19.86 -- while
the car claims 19 (doesn't display tenths) as its average -- I'm not going
to gripe that "I'm not getting what the official rating is"!