All, I'm trying to calibrate a smartphone fuel consumption application on my vehicle, a 2009 Ford Fusion SE with the I-4 engine. I want to get a "control" varible to compare against the mileage readings I'm getting from Torque's Fuel Efficiency plugin. In order to do this, I want to have exactly one gallon of fuel in the tank, and see how many miles I can drive until it runs out of gas.

The problem is, it seems I cannot rely on the Fusion's message center to give me the real number. The message center's "Miles to E" feature says I have 0 miles left until empty, but I know that the car has fuel in reserve. According to the guy at CarQuest, Ford usually gives about 2 gallons worth of reserve fuel after you've hit "empty". Can anyone confirm this, or give me the actual amout that's held in reserve on the 2009 I-4 Fusion?

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    Another good question might be whether your plan to intentionally run out of gas may have ill effects on the engine. Jun 7, 2014 at 18:40

1 Answer 1


As Nate Eldredge says, running the car totally out of fuel is usually a bad idea...

A better method of doing the same thing is the full-to-full test - fill the tank completely, drive for a known distance, then fill it again (ideally using the same pump, as they don't all 'click' off at exactly the same point). You then know the amount of fuel used for that distance, and so can calculate your efficiency.

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