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Help!! What's wrong with my gas tank/gas gauge?

Discussion in 'Gen 2 Prius Fuel Economy' started by Prius Cat, Oct 9, 2011.

  1. Prius Cat

    Prius Cat Shhh... I'm stealthy

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    Please help! About a week and a half ago, I filled up my Prius when I had 2 pips left, which is when I normally fill up. I don't like to wait until I'm at the end of the tank because I get really worried.:p I noticed that, before I filled up, I had the best gas mileage of my life. According to the screen, I had driven 392 miles, with a 42.3 average MPG. Lately, I've been very cautious about my driving (trying to get a high MPG!), so these numbers were very pleasant!!:D But, after I filled up, I noticed that I was charged a lot more than my routine weekly fill-ups. I was charge $44, when I normally pay about $34-35 (average $3.99/gallon). Upon closer inspection of my receipt, I noticed that I really filled up 11.095 gallons. This is very suspicious because I thought that the Prius 2nd Gen has a gas tank that holds 11.9 gallons. Since I had two pips left, how was it possible for me to fill up that much gas without a warning? Why didn't it give me a warning beep/notification? Is my gas gauge faulty??

    While driving on that new tank of gas this past week, I noticed that it wasn't until about 200 miles before the first pip disappeared. Isn't this odd? 200 miles for the first pip to register???

    Yesterday, I filled up the Prius again. Before filling up, I noticed that I had driven 350 miles, with an average of about 41 MPG. I think I may have had 5 pips left, but I'm not 100% sure because I didn't want to depend on that as an accurate gauge of when to fill up. But, I do know that I had more pips than expected...I assumed it was because it took the first pip so long to disappear. Anyways, my gas receipt said that I filled up 7.163 gallons. This means that, if I drove about 350 miles and only used 7.163 gallons since my last fill-up, my average MPG is about 48.9. This is impossible!! My average has never even passed 43 MPG!

    I don't know what's going on, but can anyone give me some advice? I've been driving this car for 2-3 years now and have never noticed this problem. I'm also a complete newbie with all this technical stuff. I don't really know anything about the gas tank/bladder/etc. I'm just so worried because now I don't know how to accurately gauge my mileage or know when I should fill up. Help, please!

    Thank you! :)

    Additional Info:
    I reset the gas consumption screen every time right after I fill up, so my average MPG resets every time I fill up.
     
    #1 Prius Cat, Oct 9, 2011
  2. F8L

    F8L Protecting Habitat & AG Lands

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    If the car is still under warranty then take it in to the dealer and have them diagnose it just in case the sensor is faulty. Have you had the car scanned for codes?
     
    #2 F8L, Oct 10, 2011
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  3. uart

    uart Senior Member

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    I don't think this is too unusual. You had one big fill of more than you expected (bladder probably fully stretched) and then it's natural that the next fill was less.

    I get that all the time when my wife fills the car, the calculated mileage is 70MPH one tank and 40MPG the next. It's just inconsistencies in exactly where the gas pump cuts out, magnified even more by the presence of the flexible bladder in your case.

    We don't have the bladder in the tank here (Aust model) so it's somewhat easier to get a consistent fill. When I fill the car and I'm really careful to try to pump it so it cuts out at a consistent full-point then my calculated mileage varies only a little bit (like 50 - 58 MPG), but like I said before, when my wife "fills" it the calculated per tank MPG is all over the place.

    I don't think there's anything to worry about in what you've seen over the last few tanks. Just drive it for a few more tankfuls and see.
     
    #3 uart, Oct 10, 2011
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  4. fuzzy1

    fuzzy1 Senior Member

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    Together, the two fills consumed 18.258 gallons for 742 miles. That works out to 40.6 mpg.

    Is this a normal mpg for your routes? If so, I'd write off the large refill as a simple overfill, the pump didn't shut off as soon as normal. The next small refill made up for it.
     
    #4 fuzzy1, Oct 10, 2011
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  5. bisco

    bisco cookie crumbler

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    do u fill it yourself or use full serve?
     
    #5 bisco, Oct 10, 2011
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  6. Rae Vynn

    Rae Vynn Artist In Residence

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    #6 Rae Vynn, Oct 10, 2011
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  7. EffinRed

    EffinRed Junior Member

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    You mean the "guess gauge" was off? I try not to rely too heavily on the gauge, it seems to do whatever it pleases at any given moment.
     
    #7 EffinRed, Oct 23, 2011
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  8. Prius Cat

    Prius Cat Shhh... I'm stealthy

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    Hi everyone! Thanks for the helpful comments. My gas gauge (now, I will see it more as a "guess gauge", haha) seems to be back to "normal". I guess the first fill-up was an overfill..i'm still worried though. I feel like I can't trust the gas gauge anymore! I fill it up myself.. Does that make any difference? Thanks again though everyone! :)
     
    #8 Prius Cat, Oct 24, 2011
  9. Prius Cat

    Prius Cat Shhh... I'm stealthy

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    I think this is exactly what happened.. And your calculations are extremely close to my normal MPG! Thanks for taking the time out to do the calculations (something I should have thought about doing, but somehow didn't think of it!)---it brought every thing to light and made me less worried about the situation. :)
     
    #9 Prius Cat, Oct 24, 2011
  10. KK6PD

    KK6PD _ . _ . / _ _ . _

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    Welcome to the widr world od Guess Gauge! My car does the same thing, although I only get approx 135 miles for the first pip! Rae Vynn had a good idea, reset the sensor! as you go along in life you will become accustomed to the Prius Guess Gauge! :D
     
    #10 KK6PD, Oct 24, 2011
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