Edmunds Answers

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  • avatar ray80 02/14/13 7:10 am PST

    In some vehicles sqeezing those extra drops of fuel in can allow fuel to enter part of the evap system and cause problems with it (only supposed to handle fumes, not liquid).

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  • ray80 02/14/13 7:10 am PST

    In some vehicles sqeezing those extra drops of fuel in can allow fuel to enter part of the evap system and cause problems with it (only supposed to handle fumes, not liquid).

  • Stever@Edmunds 02/14/13 8:47 am PST

    In addition to what Ray80 said, topping up too much can trigger the check engine light and sometimes damage EVAP components.

    Your fuel pump is cooled and lubricated by the gas left in the bottom of the tank so that's why it's not a good idea to run below empty. I usually wait until the gauge is near the line but my low fuel light doesn't come on too often.

  • texases 02/14/13 9:09 am PST

    And it's important not to 'top off' - we get lots of questions about evaporative control systems, OBD-II codes, and inability to rapidly fill with gas that are all related to topping off and forcing liquid gasoline where it shouldn't go.

    I bet your phone has a calculator on for the mpg calculations.

  • morin2 02/18/13 10:43 am PST

    All excellent responses. There is no good reason to overfill a fuel tank. The most I will round up is to the next nearest 5 cents, never to the nearest gallon. If you want to track your fuel economy, the best way to do it is to record every fillup in a small notebook kept in the car. I label columns as so: date, odom, trip odom, gals, $cost and mpg. At each fillup, I enter the data for the first 5 columns and leave the last one blank. When its convenient, I divide the gallons into the trip odometer and record that mpg calculation in the last column. I have done this for many cars starting with my first 42 years ago - and have gotten my wife and kids to do it. It quickly becomes an automatic part of the re-fueling process. Since I usually fill my car every other day, there are plenty of entries. Keeping a notebook is also a good way to record oil changes, tire rotations, wiper blade replacements, etc. When I sell one of my cars, the notebook goes with it. I can't think of any negative doing this.

    On our fleet vehicles at work, we have large printed warnings "DO NOT TOP OFF" to prevent damage to the emissions components.

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