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Gas (Guess) gauge woes

Discussion in 'Gen 2 Prius Fuel Economy' started by dkolars, Aug 7, 2006.

  1. dkolars

    dkolars Junior Member

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    Got the Prius at the end of April... The first time the gas bar got down to the last one and started flashing, I drove about 10 mi. to the gas station and filled up... took 10 gal. So, as it's an 11.5 gal tank, & I'm getting 40+ mpg, I "assumed" that I would be able to drive somewhere between 40-50 miles if need be to get gas after the last bar started flashing.

    About 2 mos. into having the car, I was about 5 mi. past the gas station, with another 13 to go to my destination. So, based upon my previous experience, I continued to drive, thinking that I would fill up the next day, it being only 31 miles to the destination and back. I made it about 12 miles and ran out of gas! At this point in time, I began to distrust the gas gauge, and made it a point to fill up when it reached 2 bars and monitor the gallons needed to better gauge the actual distance that could be covered with a low tank... With 2 bars left, it usually took about 7-8 gallons to fill up, and now I'm averaging about 45+ overall, so with 2 bars showing, I should be able to drive at least 90 miles at a minimum.

    Just returned from a 6200 mile trip from IL to Calif on 80, up the coast to WA, and back to IL on 90. Close to the NE/WY border is the town of Kimball, NE... 25 miles away in WY is Pine Bluffs, about 1 mi into WY... we hit the Kimball exit and the bars dropped from 3 to 2, so we continued on, intending to get gas in Pine Bluffs, as it was only 25 miles. At mile marker #2 on 80 in NE, we ran out of gas!!

    So, now the car won't even go 25 miles with 2 bars showing!! So much for thinking that it would go 90 or more!!!

    For the rest of the trip (over 5000 miles) we filled up whenever we got to 3 bars, and sometimes sooner depending on the scarcity of stations in various states (like WY!).

    So, the car is going into the shop this week for an inspection, as this is just not right! Plus, the driver's side window is nearly impossible to jog into a slightly open position, maybe 1 time out of 8 tries... the rest of the time it's full open or close...

    Anyone else had the problem with the gas gauge being so bad? It's actually worse than bad, IMHO... they can monitor the tire pressure, mpg, etc. and can't measure the gas left? Of course, no vehicle I've ever seen in over 50 yrs. of driving has ever had an accurate gas gauge, so I shouldn't be too surprised, but the huge discrepency is worrisome, especially on long trips.

    I've read all the discussions about temp, humidity, air pressure affecting things, but 25 vs. 90+ is not (to me) explainable by those variables! All comments welcome!
     
    #1 dkolars, Aug 7, 2006
  2. berylrb

    berylrb Member

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    <div class='quotetop'>QUOTE(Dave Kolars @ Aug 7 2006, 05:24 PM) [snapback]299280[/snapback]</div>
    Yeah, but Dave, if you were steadily driving on a grade or hit a pass within 90 miles of running out, I doubt you were averaging 45 mpg, which your 3 bar rule of thumb was guaged upon right?
     
    #2 berylrb, Aug 7, 2006
  3. Lil Mo

    Lil Mo New Member

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    Did you monitor the miles as well? Any comment that how many miles per tank?
     
    #3 Lil Mo, Aug 7, 2006
  4. Tideland Prius

    Tideland Prius Moderator of the North
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    Yep, I'd monitor mpg and miles per tank cause you're gonna run into the same problem when winter comes and the bladder shrinks and we're gonna have to read your posts about running out of gas even earlier.

    It's not that they can't measure the amount of fuel left properly. It's the bladder that's making the calculation difficult and the reason why it varies from tank to tank. Just trust the computer when it comes to mpg and miles (a rule of thumb is 10x the mpg is the tank miles at which you should fill up so at 45mpg, fill up at 450 miles)
     
    #4 Tideland Prius, Aug 7, 2006
  5. Renocat

    Renocat Member

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    WIth all the discussion about the "guess gauge" and running out of fuel, a thought has been running through my blonde head (bear with me!)

    The MPG shown on the MFD is an average. If it is showing 45 mpg that theoritcally would mean that you were achieving 90 mpg 1/2 the time and achieving 0 mpg the other 1/2 of the time. If you are down to 1 pip, why would you assume that you are going to achieve 45 mpg when that very well could be the time that you will achieve much less to make it average out to 45?


    And another thought I have is I was always told by my father and brother (both auto mechanics) that the gas guage drops quicker for the second 1/2 of the tank. In other words, it takes longer to drop from full to 3/4 than it does to go from 1/4 to E. Don't know if it is true or not but it did seem to do that in my previous cars.

    Just my 2 thoughts...please don't hate me for my blondness :lol: :lol: :rolleyes: :lol: :lol:
     
    #5 Renocat, Aug 8, 2006
  6. eagle33199

    eagle33199 Platinum Member

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    You're mostly correct... except that, as an average, it doesn't mean 90MPG and 0. it just means that half the time you're over and half you're under (roughly - that would actually be the median, but you get the idea). I think the key point to remember is that, in a normal car, you generally don't run it to empty. My last car i would run it until i had about 1/4 tank left, and refill (most of the time) and never had a problem. i would also watch my miles (until my trip odometer broke) and my fill ups almost always happened between 260 and 280 miles. I don't see any reason to change your habits in the Prius. just because you have more information at your fingertips (being MPG), doesn't mean you aren't running the same risk as in any other car by letting the gauge drop down to empty.

    Now, the experience posted where you got very little with 2 bars showing is a bit questionable. However, you also have to consider other factors, such as the incline of the road, which weren't present. Even in my last car, i would see the needle increase or decrease a little with the inclination of the road, and knew that it wasn't exact.

    Also, never expect that you have a certain number of gallons in the tank from a refill. the bladder just makes it too unpredictable. you might think you have 11.5 gallons, but unless you actually put 11.5 in during the refill, you really don't know. (you might have put in 9.5 but figured that with 2 bars showing you still had 2 gallons left) Never assume!
     
    #6 eagle33199, Aug 8, 2006
  7. Tideland Prius

    Tideland Prius Moderator of the North
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    <div class='quotetop'>QUOTE(Renocat @ Aug 8 2006, 07:44 AM) [snapback]299581[/snapback]</div>
    Hmm... mine's the opposite. After x kms before the first pip goes, the 2nd to 5th pip goes every 50kms and the bottom half goes every 80kms which means my tank distance is determined by how many kms before my first pip disappears :lol:


    This is what I've been observing since April
     
    #7 Tideland Prius, Aug 8, 2006
  8. Renocat

    Renocat Member

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    I haven't really noticed if that holds true for my Prius. Just something I had been told for the last 30 years or so.
     
    #8 Renocat, Aug 8, 2006
  9. mcsj

    mcsj Member

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    <div class='quotetop'>QUOTE(Dave Kolars @ Aug 7 2006, 05:24 PM) [snapback]299280[/snapback]</div>
    That section of i-80 are pretty much climbing up the Rocky Mountains. I think we should expecting a low gas mileage, and (I think, just like all other cars) the gas gauge becomes bias when the car is not level. One thing I am interested in -- did the gas gauge say empty when your Prius went out of gas?
     
    #9 mcsj, Aug 8, 2006
  10. kquinty

    kquinty New Member

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    I also ran out of gas in my 2006 Prius. I've had the car since May 2006 and I was driving on the highway when the fuel guage went to one bar and started flashing. The gas station I planned to stop at was 10 miles away, so I just kept driving, thinking this warninig was juat like the low fuel warning light on other cars. For example, My wife's BMW X3 has 3.5 gallons remiaing in the tanks when the light comes on. Well, the Prius ran out of gas 5 miles after the guage started flashing. I was monitoring the trip computer which said I was averaging 49 MPG, which means I should have easily gotten past the 510 mile mark where I ran out of gas.

    There is a happy ending to this story. I was only about a mile from the nearest exit when the engine stalled, but the car ran on electric power to the gas station and there was no walking or hitch hiking or AAA needed.
     
    #10 kquinty, Aug 8, 2006
  11. dkolars

    dkolars Junior Member

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    Thanks for the insights and thoughts about the guess gauge... As to the miles per tank, that's not a good measure for me... I don't trust the gauge, so when is "a tank"?? I kept records for the entire trip and found that:
    Gal Miles MPG Place
    10.075 504.10 50.035 Oceola, IA <-- 1 bar showing
    8.435 381.90 45.276 Belleville, KS
    11.340 464.80 40.988 Pine Bluffs, WY <--- this is the one where we ran out... 2 bars showing, added a gallon from the policeman's can, and still took 11.3 Gal. 4 miles later!!
    8.029 324.10 40.366 Rock Springs, WY
    7.540 370.90 49.191 Wells, NV
    7.840 350.70 44.732 Boomtown, NV
    7.885 416.90 52.873 Gerberville, CA
    5.593 240.70 43.036 Grant's Pass, OR
    6.325 305.30 48.269 Woodland, WA
    7.790 330.20 42.388 Bellingham, WA
    8.000 360.00 45.000 Ellenburg, WA
    8.753 379.10 43.311 Missoula, MT
    4.570 207.90 45.492 Bozeman, MT
    6.509 326.50 50.161 Greybull, WY
    7.845 340.00 43.340 Rapid City, SD
    7.106 302.00 42.499 Mitchell, SD <-- HOT weather
    7.563 278.80 36.864 Hutchinson, MN <-- HOT & HUMID weather!!! BIG Difference
    8.723 341.30 39.126 Dyersville, IA
    8.810 395.00 44.835 Plano, IL

    Overall average for the 6220 miles was 44.670 -- as you can see, we started filling up a lot earlier after we ran out! 3 bars means that I have used about 8/11 ths of my fuel, or .7272... this is about right, as there are 10 bars, and 3 left means that I've used 7/10ths... but, if I'm on the open road, averaging even 42 mpg, with 2 bars left, I shouldn't run out, going uphill, downhill, sideways, or backwards... I monitor the MPG indicator constantly, as this helps me to drive more effeciently, and on the open road, it was always in the range of where that tankful's average was...

    I'll never trust it again... the alluding to filling up when one is 1/4 full is good, and I learned to drive that way some 50 yrs. ago, but the cars then got slightly less mpg than the Prius, and the gas stations were scarcer!

    After being home since Tuesday, I filled up today:
    6.250 Gal 323.90 Miles 51.824 MPG

    And that is town, highway, city, etc. 4 bars showing.
    DK
     
    #11 dkolars, Aug 8, 2006
  12. bad monkey

    bad monkey New Member

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    I think others have used this trick to calculate a better "gauge": Take the amount of fuel that you added at your last fill up and make a conservative guess at your current MPG. Since you could not have misplaced fuel, this should always work regardless of bladder incontinence.
     
    #12 bad monkey, Aug 8, 2006
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