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False Fuel gauge readout?

Discussion in 'Gen 2 Prius Technical Discussion' started by chinito77, Jun 14, 2007.

  1. chinito77

    chinito77 Member

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    My 06 Prius is now past 10,000 miles. My Balitmore to DC work commute is racking in the mileage and averaging 48.5 MPG right now. Anyway, twice I have notice that when I fill up my usual 5 gallons (since gas is above $3.25), I'm still at 1 bar on the fuel gauge. The first time I thought the gas station was rigged but noticed I was able to drive 3 days on the one bar before I got my "Low gas" message. I filled up to the usual 5 gallons and the digital bars on the fuel gauge got near Full.

    Days later, when I was back at one, I filled up the usual and it stayed at 1 bar. Again, I was able to drive 3 days on this one bar. Being nervous, I filled it up before seeing the "Low on Fuel" message. So, has anyone else encountered this? Suggestions or comments? :unsure:
     
  2. Stepclimb

    Stepclimb Junior Member

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    The fuel gauge is notoriously innaccurate. You can do a search for "guess gauge" and see the many threads regarding its inaccuracy.

    That being said, I'm not sure I would drive around with only one bar showing. Most of the time, I fill up when I get to 2 bars. Is there any reason you are only putting in 5 gallons at each fill-up?
     
  3. JimN

    JimN Let the games begin!

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    <div class='quotetop'>QUOTE(chinito77 @ Jun 14 2007, 06:10 AM) [snapback]461453[/snapback]</div>
    Do I detect the heart of a hypermiler beating in your chest? Another 30 pounds of gas (a full tank) may recalibrate the sensor. Where is your tp? Blocking the upper grill will also boost mpg.
     
  4. chinito77

    chinito77 Member

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    <div class='quotetop'>QUOTE(Stepclimb @ Jun 14 2007, 03:55 PM) [snapback]461819[/snapback]</div>
    $10 will get me ~3 Gallons. $15-$20 will usually get me 5 gallons. I try to never spend more than $20 on a full up. There was this myth about running your tank to empty was bad for you car that I learned in drivers ed. Nowadays I don't know if it has a factor on a hybrid or not.

    Now, I'm a horrible Hypermiler. I do what I can under favorable conditions. The roads seem too hilly which causes me to burn more gas as I lose momentium and need to catch up with the flow of traffic. On top of that, I feel comfortable at or near 70 MPH. I'll take getting home 10 mins early over saving a few cents per fill up. :p

    Also, can I get some more info on blocking the upper grill??
     
  5. wbuttler

    wbuttler New Member

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    For what it's worth my 2007's gas gauge is completely inaccurate and inscrutible.......

    100 + miles without movement then sudden movement to a new position....

    I keep a toshiba 110ct libretto subnotebook laptop in the car for record keeping and
    i'm hoping to find some type of pattern on the gauge.

    all the best
    froley
     
  6. daniel

    daniel Cat Lovers Against the Bomb

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    Just a thought off the top of my head: Try filling the tank once, until the nozzle clicks off, just to see what happens.
     
  7. qbee42

    qbee42 My other car is a boat

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    Partial fills will throw off fuel computers on many cars. When you do a partial fill, the system has to work on just the float level, which is never completely accurate, and really bad on the Prius. Follow the previous poster's suggestion and fill it up.

    Tom
     
  8. pkhoury

    pkhoury Proud TDI owner

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    <div class='quotetop'>QUOTE(Froley @ Jun 15 2007, 09:20 PM) [snapback]462843[/snapback]</div>
    Makes two of us. I log all my mileage on my ThinkPad T42p, all the way back to when I first
    got the car.

    After 90-130-ish miles, the gas gauge goes down one notch. The only time it's even remotely accurate
    is when it's half empty.

    And are there long term bad effects to driving on empty? Thanks to the gauge being inaccurate,
    I made it on empty until I had one bar for my battery because I ran out of fuel. Apparently, the Hybrid Synergy kicks in and you can only drive very slow, although it stalled twice (both times, about 150 feet from the gas station).

    Paul
     
  9. richard schumacher

    richard schumacher shortbus driver

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    1. Running out of gas in a Prius does not do the battery any good. Don't make a habit of it.

    2. Running out of gas in any modern car can damage the fuel pump because the pump is cooled by the flow of fuel. Replacing the fuel pump in a Prius requires replacing the fuel tank because the pump is inside the tank. You really don't want to pay for that.
     
  10. JimN

    JimN Let the games begin!

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    <div class='quotetop'>QUOTE(chinito77 @ Jun 15 2007, 10:22 AM) [snapback]462308[/snapback]</div>
    The definite thread must be "My first day with a blocked grill". Best ROI. I'm curious. When are you driving on I-95 and the Beltway so you can do a constant 70mph? It seems the Beltway is either Indy qualifying trials or a parking lot.
     
  11. pkhoury

    pkhoury Proud TDI owner

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    <div class='quotetop'>QUOTE(richard schumacher @ Jun 16 2007, 02:54 PM) [snapback]463126[/snapback]</div>

    But this happening once isn't severely detrimental, right? The less stuff I have to replace
    over the life of my Prius, the better.
    Although I can't wait to see the supposed new version that gets around 80EPA (which is what, about 60 actual?).

    PK
     
  12. justifyd

    justifyd New Member

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    <div class='quotetop'>QUOTE(pkhoury @ Jun 16 2007, 06:20 PM) [snapback]463151[/snapback]</div>
    Probably not. But that's a dangerous game of chance that nobody wants to lose.

    As far as the original topic here, I'd like to pass along an idea I once heard. If you are committed to the partial fill-up, perhaps you should completely fill it once and then plan your refueling stops so that each one fills the tank again. In other words, calculate how far those five gallons will get you and refuel once you've traveled that distance.

    Bonus benefit: You'll have a nice "reserve" of fuel on hand in case you can't get to the station right away.

    In addition to concerns about the fuel pump are concerns about drawing impurities into the fuel system. I don't know how the bladder affects that, but in hard-shell tanks the impurities usually collect at the bottom.

    - Justifyd
     
  13. vdubstress

    vdubstress Junior Member

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    <div class='quotetop'>QUOTE(qbee42 @ Jun 16 2007, 01:34 PM) [snapback]463094[/snapback]</div>

    I think you meant to say really bad on every Toyota. :D I've never driven any other brand that has such a hopelessly optimistic fuel gauge in the first quarter, then between 3/4 and 1/4 of a tank if you're really bored you can sit and watch it move downward, and then hang in the last quarter for an eternity! I figured the in tank bladder would improve the guess gauge on the Prius, but nope, it is the same as every other Toyota.
     
  14. JimN

    JimN Let the games begin!

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    <div class='quotetop'>QUOTE(pkhoury @ Jun 16 2007, 06:20 PM) [snapback]463151[/snapback]</div>
    Many people hit or beat the EPA number before the test was revised causing lower scores. Many more people will hit or exceed the "new" EPA number. If Toyota says the next gen gets 80mpg I believe it. Check out www.greenhybrid.com to see real world mpg.
     
  15. glennsferryprius

    glennsferryprius New Member

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    <div class='quotetop'>QUOTE(pkhoury @ Jun 16 2007, 04:39 PM) [snapback]463095[/snapback]</div>
    I just got my 2007 Prius, and I have logged all but 2 miles (that was on the car when I took delivery Friday). I realize that it is only 700 miles, but I noticed that the first (last?) bar took about 100 miles to turn off, the the others hurried on down so fast that I thought I would risk running out and have to fill before my normal second stop on my Twin Falls Idaho to Spokane Washington route. I had so much faith in all I read about the Prius, that I bypassed my usual first stop. It got down to 2 notches and stayed, so I fueled as usual in Pendelton Oregon. Computer said 51, calculator said 46, and either way I'm happy. I just want to learn how to interpret the gauge. Or just use one of the trip odometers.

    Having seen other vehicles towed out of the southern Idaho roads during the hot days of the summer (usually failed fuel pumps according a friend that worked as a servicewriter in several dealerships), I don't want to take the chance.
     
  16. SaxyBiz

    SaxyBiz Junior Member

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    <div class='quotetop'>QUOTE(Froley @ Jun 15 2007, 11:20 PM) [snapback]462843[/snapback]</div>
    Inaccurate, Yes, but predictable. If I top off the tank, I get 125+ miles before the first indicator goes off. It depends on how much I overfill how long it takes for the first indicator to respond, it could go 150 miles. It doesn't matter how much gas you put in, the indicator won't respond until the overfill of fuel is used up. THEN it is very non-linear but accurately predictable. The next indicator will go out a about 36 miles, the seventh one at another 26 miles, the sixth/half tank indication will happen in another 45 miles, and the last half I haven't charted yet.

    I don't know if this is the case for others, but I can count on these figures on my Prius. I'm concerned that by the time I chart the last 1/2 tank, I'll run out of gas. I end up filling the tank again before the weekend when they hike the prices!! I hope this helps.
     
  17. relsley

    relsley New Member

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    <div class='quotetop'>QUOTE(chinito77 @ Jun 14 2007, 03:10 AM) [snapback]461453[/snapback]</div>
    I had a similar experience. Before leaving on a 400 mile trip, the gas gauge was at 1/2, so I filled the tank, putting in between 3 & 4 gallons. The miles and mpg reset to zero as expected, but the gas gauge stayed at 1/2. I drove 200 miles and the gauge stayed at 1/2 the whole way. I then filled up again, and this time, everything reset properly. It hasn't happened again.
     
  18. chinito77

    chinito77 Member

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    Balt-Washington Pkwy in the early mornings can be pretty bare. Lots of speeding pickup trucks in Maryland but I do my best and stay with the pack. It's after work that I encounter heavy traffic leaving D.C. It's during this that I do wonderful on MPG.

    As for the fuel thing. Just did full tank of gas from Maryland to Long Island, NY trip and filled up on the way back in NJ. I didn't want to chance it as the readout was at 3 bars which would be normal but I feel so uneasy now about relying on it. I'll try to change my habit of topping off. It would be better for my car.
     
  19. Marlin

    Marlin New Member

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    <div class='quotetop'>QUOTE(Froley @ Jun 16 2007, 12:20 AM) [snapback]462843[/snapback]</div>
    So many people get bent out of shape about how the guage stays at Full for a 100 miles or so before it starts dropping.

    I guess they never paid close attention to the analog needle gas guage on their previous car. If they had, they would have noticed that on a full tank, the needle most likely swung past the "F" on the guage and stopped on a peg on the top of the guage. The needle would most likely remain on this peg for many miles before it would move off it and then would take more miles before it dropped below the "F" line on the guage.

    The digital guage in the Prius is no different. In the Prius, the "needle" gets digitally "pegged" at 10 bars. On an analog guage, the needle gets physically pegged on a real peg. The effect is the same.
     
  20. ZA_Andy

    ZA_Andy Member

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    <div class='quotetop'>QUOTE(Marlin @ Jun 19 2007, 12:47 PM) [snapback]464740[/snapback]</div>
    With the added factor that on other vehicles with their analog gauges, the rate of fuel use causes the needle to drop rather faster than the rate of fuel use causes the 'needle' to drop on the Prius, so making the lingering around full rather more apparent.