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Old 05-03-2013, 10:52 PM   #1 (permalink)
Your car looks ridiculous
Join Date: Jul 2012
Location: Northern California
Posts: 96

The Fantastic Festiva - '90 Ford Festiva L
90 day: 43.16 mpg (US)

A Civic Duty - '96 Honda Civic LX
90 day: 34.9 mpg (US)

Ranger Danger - '96 Ford Ranger XL
90 day: 17.42 mpg (US)
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I've got a fuel economy math problem!

So I had a full tank, drove 310 miles, then decided to go to the other gas station because it's tire pressure machine works better than my usual reliable station. Expensive Chevron gas station, but the fuel pump was terrible. It kept clicking off. I expected this from the old discount gas station I used to use with it's un-calibrated fuel pumps and dangerous neighborhood where I fear getting mugged or car jacked every single time I fill up, but not with expensive Chevron gas. For the record, in the past I didn't buy into that whole fuel quality deal, but after some research, I really do believe there is a difference in fuel quality and additive packages and so on.

So the fuel pump shuts off over and over. I decided to stop out of disgust. I pumped 6.392 gallons, which did not fill the tank.

Then I drove 362 miles, making the total 672 miles. Pumped gas at my usual #5 pump at my usual gas station, and I loved it. I missed it. No clicking off. Just perfect fluid smooth flow. 11.112 gallons.

Now is there any way I can calculate my fuel economy from all of these numbers, using strange magic like algebra or something? Does knowing the full tank capacity of my car, which is 13.2 gallons, helpful at all? Or is it impossible? Lol, this problem should be on a high school math test. Or we should be able to answer it in order to get our eco-modding license in order to do legal eco-mods in the state of California. Hah. I don't like myself.

Total Capacity = 13.2

Fuel Pumped = 17.5

Total Mileage = 672

13.2 - 6.392 = 6.80
13.2 - 11.112 = 2.09

Are these numbers useful/useable?

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Old 05-03-2013, 11:30 PM   #2 (permalink)
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Diesel_Dave's Avatar
Join Date: May 2011
Location: Indiana
Posts: 1,194

White Whale - '07 Dodge Ram 2500 ST Quad Cab 2wd, short bed
Team Cummins
90 day: 37.68 mpg (US)
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Using the same pump at the same station every time definitely helps, but you'll still have fill variations. Some of it just depends on the fuel tank, how it's shape can change since it's made of a thin-walled material. Also, you can get air pockets in the tank as well--they don't always come out consistantly.

It can be frustrating, but in the end it all comes out in the wash. One tank may look artificially low and another artificially high, but it all averages out.
Diesel Dave

My version of energy storage is called "momentum".
My version of regenerative braking is called "bump starting".

1 Year Avg (Every Mile Traveled) = 47.8 mpg

BEST TANK: 2,009.6 mi on 35 gal (57.42 mpg): http://ecomodder.com/forum/showthrea...5-a-26259.html

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Old 05-03-2013, 11:52 PM   #3 (permalink)
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Location: Texas
Posts: 3,523

The Q Sold - '02 Infiniti Q45 Sport
90 day: 23.08 mpg (US)

blackie - '14 nissan altima sv
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total gallons and total miles driven.

that's it.

When I was taking my many trips from CA to Tex, I would sometimes have to get a couple of gallons when I was running low but knew there was cheaper gAS ahead.
I would just add those gallons to the amount used to fill up. And keep the odometer running.

Total miles driven and total gallons but in the tank.

Fuel Pumped = 17.5

Total Mileage = 672
MetroMPG: "Get the MPG gauge - it turns driving into a fuel & money saving game."

First: ScangaugeII

Second: Grille Block

Third: Full underbelly pan

Fourth: rear skirts and 30.4mpg on trip!
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Old 05-04-2013, 02:23 AM   #4 (permalink)
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Join Date: Oct 2010
Location: sweden
Posts: 1,182

Princess - '92 Mazda MX-3 GS
House of Tudor
Team Mazda
90 day: 53.54 mpg (US)
Thanks: 46
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Let me google that for you.

2016: 128.75L for 1875.00km => 6.87L/100km (34.3MPG US)
2017: 209.14L for 4244.00km => 4.93L/100km (47.7MPG US)
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Old 05-04-2013, 02:29 AM   #5 (permalink)
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Join Date: Apr 2012
Location: Saskatchewan
Posts: 114

Eric's Explorer - '01 Ford Explorer Sport 4x4
90 day: 19.05 mpg (US)

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Miles per gallon

You drove 672 miles on 17.5 gallons

Divide the 672 miles by the 17.5 gallons

672 miles / 17.5 gallons = 38.4 miles/gallons or 38 mpg.

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