It's actually not recommended to top off because 1) the fuel will spill when your corner, 2) you need a little vaccuum in the fuel tank.

 

this is how you do it, how empty dont matter its simple
miles driven/amount= mpg

of course this only works if you started with a full tank and watch your miles perfectly, and of courst know how to add subtract multiply and divide

 

I did this test and got an average MPG of how I drive and when I filled it up to 10 gallons I ended up with around 304miles in total till I had to refill the tank to 10 gallons again. So for my personal driving habits on my Civc98Ex I'm averaging about 30-33mpg. This accounts for both Highway and City driving. Not too shaby if I may say.

 

You don't even need to drive a whole tank's worth. I did some MPG tests at the Gas Savers link in my sig. Each test consisted of topping off, driving around 80 miles on the highway, returning to the same pump and topping off. You have to be sure to situate the pump in the same orientation as the first time and let the auto-cutoff do it's job.

The results were very accurate, and you can even see the effects of temperature on MPG (yes it plays a big difference, about 3MPG for 16 degrees difference for me). If you make a best fit curve for the data (vs. temperature), each data point is well under 0.1MPG from the curve. Even with short trips, this method is very accurate. You have to be consistent in your driving though, and city driving is not consistent enough.

There is a device called ScanGauge for OBD2 equipt vehicles. It'll tell you instantaneous MPG and average MPG. It works off measuring the length of your fuel injector pulses and combines that with the speed sensor to get MPG.

 

i know im still a newbie but this one makes my head hurt.

as said before:

1)start with a full tank and 0,000 on the trip odometer
2)drive around*
3)fill up again
4)divide the number on the trip odometer by the number on the pump (the number under the number that has a $ next to it)
5)just be happy that the number is over 25 and that youre not driving a hummer

*does not matter if you drive 70 mi, 170 mi, 270 mi. doesnt matter if your gas light comes on after 15 min of driving or not until your completely empty or if your gas light doesnt come on at all. doesnt matter if your gas light is green or purple or red. doesnt matter if your tank carries 11.3 gal or 5,769,311.3 gal. yes it may be slightly more accurate if you wait til closer to empty but the ONLY way to be accurate is to average it out over multiple fill up's.

can we be done now?

mike

 

I wouldn't have bought my Civic unless I knew for certain that it would be able to stay in the 30's while city driving for MY driving habits. I would have been very dissapointed if I was anywhere in the 20s even the high 20s expecially since this is an economy car.

 

sorry

 

ok there is no way to really measure your milage off one tank with any real level of accuracy. If you really want to know, do over like ten tanks, so any differences between pump shutoffs or whatever else is mimized.

 

Don't know what you mean by pump shutoff. If your refering to the gas pump in the car shutting off for some random reason then that has never occured unless I turned on the car alarm while driving. If your refering to the gas pump at the station then still I've yet to encounter that. I always use 1 pump and never get gas when its being filled by the gas tanker. I also get the gas at the same time of the day each other week.

The 10 tank test requires you to log down numbers through a very long course of time which can involve more variables than 1 tank test. I fill my tank once every 1.5 weeks and for 10 tanks thats about 3.5 months. Alot of variables of driving habits and climate changes along with mechanical issues can easily flux the numbers greatly.

At least with 1 tank, you greatly limit the external and internal variables and get the results at that point of time. Not after logging numbers down when times and conditions change in the course of months.

You most certainly aren't going to get an accurate quarter mile average time when logging numbers from the summer to winter when nothing has changed about the car or driver except the climate. Of course your winter times will give you better results than the summer times. Same diffrence with all the variables in this gas test as well.