The error in determining Miles/Gallon....

Hadn't checked mpg for a while and noted down my miles and the gallons used by The Phoenix -
a '93 two door hatchback, 3 cylinder 5 speed manual.

For 367 miles on 7.86 gallons, I get 46.7 mpg.

However, I usually do the infamous and discouraged "Top Up" which often does
an overflow and gas is all over the gas cap area.

Anyway, I was wondering how much difference would result from slight differences
in filling the tank - what is "Full" ?

I don't always do the "Top Up" thing.

So - if one were to be 1/4 gallon off (one quart) by not "topping Up" to the overflow point - here is the result:

Plus or Minus 0.25 (one quart) gallon using the data above.....

367 miles

7.86 - 0.25 = 7.61 gallon............48.2 miles per gallon

7.86 + 0.25 = 8.11 gallon............45.2 miles per gallon

So, for the normal Geo Metro fill-up, if there is one quart of gasoline variation
from fill to fill while monitoring mpg's, one can get 3 miles per gallon difference!

That is enough to bother some folk (who are anal) like me....

If not careful, the difference in a "fill" might be even more than one quart of gasoline!

So, probably three tanks full's over a period of time averaged out is better -
but then we drive differently each week (some of us) and the temperature changes can affect the mpg quite a lot....

Just some thoughts to fill the long drives to town and back.....

DoctorBill

You're exactly right Doc, and I think you're being conservative with only a half gallon swing. I've put in a gallon after the pump kicked off. There's a ton of variables, only constant monitoring is meaningfull.

Instead of "topping off" I wonder if you just stop adding gas once the automatic shutoff kicks off at the pump the first time if that would be more accurate?

I am like you DOCTORBILL, very anal about that! I have not tried practicing what I preached above...LoL.

Oh, have you seen they have re-rated the "actual" sticker MPG's for Metros out on http://www.fueleconomy.gov/feg/findacar.htm ? The 5 speed is now rated at 38 MPG city and 45 MPG highway compared to the "official EPA window sticker MPG" which was 45 MPG city and 50 MPG highway!

THAT is really cute!

EVEN The Polypticians who run the GUBMENT say that a 2007 Honda Civic Hybrid
gets 42.8 mpg while the '93 Geo Metro 3 cyl gets 45 mpg.

My old rebuilt banger gets 49.6 routinely on plain old regular - even CENEX that
is 10% ethanol!

Some hideously expensive NEW car gets lower mpg's than an old Geo Metro!

How 'bout that!?

Why do the environmentalists push these battery-hydrogen-electric-atomic-pooie-doo
politically correct cars when there is one that does the job better with stuff we already have....?

The world is so full of b*llsh*t.....me too!

We need a car that will run on that! Just hook your TV to it and tune in CNN!

DoctorBill

THAT is really cute!

EVEN The Polypticians who run the GUBMENT say that a 2007 Honda Civic Hybrid
gets 42.8 mpg while the '93 Geo Metro 3 cyl gets 45 mpg.

Why do the environmentalists push these battery-hydrogen-electric-atomic-pooie-doo
politically correct cars when there is one that does the job better with stuff we already have....?



Not only push, the government is using our tax money to subsidize these fake economy cars. To multiply the insult, it was government safety regulations that killed the car we love so much.

Enough is enough, Ron Paul for President!
http://www.ronpaul2008.com/

I have a 90 GEO 1 lt and I put about 75 hiway miles a day 5 days a week and I go 70 to 65 mph (lead foot),now when I bought car inwinter of this year I got 35-38 mpg then valve burnt open I got 25 mpg, rebuilt now I up to 37-39 mpg. I checked egr for carbon build up none is that normal for this year? any suggestions what if I should be getting better mpg to do?

First off - expect lower mpg in the winter!

Some gasolines have 10% (or more?) Ethanol in them for less power per gallon
of gasoline...

Timing would affect mpg - if I am not wrong.

Tire inflation affects mpg's - keep the tires at 35 - 40 PSI!

Spark plugs affect it - I use platinum (Bosch or NGP).

The way you drive affects it - lead footing it lowers mpg as does flooring the
accelerator - lower efficency during hard acceleration.

City driving lowers mpg.

Put the car in neutral going down big hills - coast.
Not legal in some areas - but many things are not legal - many!

Maybe someone will chime in with more things that control mpg.

DoctorBill

Rulemob, if your GEO is an automatic, then you are getting great MPG. If it is a manual, then there could be a host of things affecting your MPG that can be found throughout this forum.