That Darn Gas Gauge Again

Discussion in 'Gen 2 Prius Fuel Economy' started by stuhillman2004, Apr 27, 2004.

  1. stuhillman2004

    stuhillman2004 New Member

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    So, I'm on my 7th tank of gas and feeling good about not having any of the fuel filling problems I've seen posted. Got home Monday evening, 395 miles on the meter, three bars on the gas gauge, 50.2mpg average, so I don't need to fill up until Tuesday evening after my 80 mile round trip commute. Cool!

    Jump in the Prius this morning (Tuesday), 395 miles on the meter, one bar flashing and the ding ding ding of the "Add Fuel" warning! I stopped the car (reboot the computer?) to no effect. Now what? No one broke into my garage to steal the gas - there is a far more inviting Dodge Caravan outside with a big gas tank, not touched.

    When I filled the tank it took 8 gallons which is consistent with the 395 miles and 50.2 mpg. It doesn't sound like a bladder problem but a computer that got out of sync with the overnight mail. Any ideas?
     
  2. Wolfman

    Wolfman New Member

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    Welcome to the world of the guess guage. It is really the only true problem with the Prius. I have yet to see mine act the same way between two tanks of fuel with identical mileage throughout the tank. Oh well.
     
  3. Tempus

    Tempus Senior Member

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    I'm looking forward to the day I can put in 8 Gallons!

    Actually, I did get in 8.1 once, but that may have been the pump cheating me :)
     
  4. m4prius

    m4prius New Member

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    I assume temperature swings could cause the flexible fuel bladder to expand or contract...especially if it goes from cold to hot the bladder may relax and thus show less fuel. Hot to cold weather may show a more fuel condition??? This could occur overnight. Has someone confirmed this???
     
  5. jimvitz

    jimvitz Junior Member

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    My experience this morning was just the reverse. Yesterday afternoon I had 5 bars showing at about 280 miles on the tank, with the temps in the 60's. Overnight, it cooled to the 40's and when I started up this AM, there were 3 bars showing.
     
  6. Astroprius

    Astroprius New Member

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    I've noticed that the fuel gauge will change when cycling the car on and off. This seems to be more frequent when the gauge is showing 4 - 7 bars remaining. Seems like I can go 20 - 30 miles between bar segments if I've shut the car off during that period. If I have a constant on drive I think I can go 50 - 60 miles before a segment change. Kind of frustrating when you have x bars when you go to a store (or other destination) and then find you have x-1 when you come back out a few minutes later.

    (Perhaps SE/SS is playing tricks on me? :wink:
     
  7. stuhillman2004

    stuhillman2004 New Member

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    This sounds like it could be the answer. You might recall that the temperature dipped down into the thirties that night. The bladder would have contracted under those conditions - although if the bladder contracts you might think it would show more in the tank, not less. Do you know if anyone has correlated air pressure differences when a cold front passes through the area? It's an interesting subject though, isn't it?
     
  8. mikepaul

    mikepaul Senior Member

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    It seems to have little to nothing to do with temperature here.

    Drive 522 miles in one day, and you get 1 unblinking bar after 10.6 gallons have been used.

    Drive 417 miles over two weeks, and when you start the car you have 2 bars for a few minutes then straight to 1 *blinking* bar just 100 yards down the road. I could only get 8.9 gallons to go into the tank.

    So if the tank empties quickly, the gauge does a good job of reflecting remaining gas. Slowly, it just sucks...
     
  9. rflagg

    rflagg Member

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    This morning I filled, it was 16 degrees cooler than yesterday morning - we were at 48 this morning. Car had run 492 miles, 51.4 or so mpg, and the pump clicked off at 6.9gals. With slow filling after the click off, I was able to put in to 9.502gals with no spill.

    -m.
     
  10. john1701a

    john1701a Prius Guru

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    I've noticed a pattern...

    We've had quite a number of gauge reports that include pump comments. And since we know for a fact that pump designs are different throughout the country and their behavior differs even at the same gas station, it seems as though that is the actual root of the problem.

    The pump is amplifying the effect of the gauge.

    That would explain why I've never even witnessed the problem some owners have been reporting. It also explains why it is not consistent from Prius to Prius.

    Who else uses ONLY the same pump at the same gas station all the time and never tops off? I bet those owners see the same reliable gauge behavior I do.
     
  11. cybele

    cybele New Member

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    I could spit right now I'm so peeved.

    I'd been running around since Wednesday with the add fuel warning - it came on at 220 miles and I was at 48 MPG (but I'd only put in 6 gallons last time, so my range by calculation is about 300 miles).

    So I went another 30 miles and filled up. It was 106 degrees! I thought that'd make for a nice pliable bladder. (I usually fill up in the morning on the way to work and it's only in the sixties.)

    Still, I only got 6 gallons in.

    So either may car is very full right now (because I got more gas in than I used from my last fillup) or my bladder is so tight it won't hold more than eight gallons.

    If I continue to get 48 MPG, I'd like to have a range of 8 gallons at least (which'd be a healthy 375 miles or so).
     
  12. chris_b_01

    chris_b_01 New Member

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    Just something about this made me burst out laughing

    sorry - just my sense of humor

    ... now.... need a restroom break


    Chris
     
  13. john1701a

    john1701a Prius Guru

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    > Still, I only got 6 gallons in.

    That kicks in the pump question...

    How do you know 6 gallons is all it would take?

    ...and/or the "full" question...

    Were you actually close to empty?


    Being able to seperate pumping issues from the actual behavior of the gauge will help get to the heart of the problem. My theory is that if you forced the distance and began filling consistently, the problem would end.

    Since my gauge works fine, I get frustrated myself with "gauge" issues others are having. There is some other underlying cause that hasn't been well researched yet, not the gauge itself.
     
  14. cybele

    cybele New Member

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    Again, I ask, how do I know that? I only know for certain (as certain as I can be) that there was as much gas as I put in there last time - 6 gallons. I'd driven 270 miles at 47 MPG - so I had pretty much used up all the fuel I put in. I'm uncomfortable driving further than what I put in, especially since I was going up into the mountains and it was 100 degrees, not a pleasant situation to run out of gas in.

    I think you're probably right, and if I'd been in the city, it would have been easier. (We probably should have taken the other car.) I have been forcing the distance where I can, but I've never gotten more than seven gallons in.

    I don't think it's my responsibility when I buy a car to spend 3,000 miles breaking in the tank in this way. Or if it is, I would like a little direction from Toyota in this regard. (But I do appreciate you commenting, John, 'because you're probably better than Toyota.)

    It seems obvious that it depends on the car and probably the driver. I am unwilling to force gas into the tank and unwilling to drive more than two gallons past the add fuel warning, so I guess I will never break my car in properly.

    My husband wants me to take it to the dealer, but I'm not due for my oil change for another 2,000 miles (and for me that'll be another two or three months), so I'm not sure if I should make a special trip.

    But my request would be rather simple. I really only want to know how much is in my tank when it's full. I may well have a gauge that reads add fuel when I have 5 gallons left, which is fine with me, if I knew that were the case. Then I'd just keep going another 100 miles or so and get a full 350-400 mile range which I'd be absolutely delighted with.

    Thanks for your comments John, you really are a rock when it comes to this stuff.
     
  15. john1701a

    john1701a Prius Guru

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    > you really are a rock

    Unfortunately, that translates to stubborn sometimes. Other times, it is in my favor as "strong willed".

    Whatever the case, I'd sure like to get to the bottom of the problem. And not being able to recreate the situation myself makes for quite a struggle.

    With the classic Prius, we came through with flying colors on the tire issue. I'd sure like to be able to do the same with whatever the heck is making the gauge behave badly.
     
  16. cybele

    cybele New Member

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    Oh I meant it in the most favorable way - you're steady and level-headed and always there to answer on these issues.

    My feeling is that my bladder is fine but my gauge is off. I think my car just tells me to fill when there's still 6 gallons in the tank (half!) instead of two or three.

    I will ask when I take it in for the first oil change (maybe I'll go early) to look at. Any clue if they'd be able to empty and refill the tank and give me an answer to how much is in there?
     
  17. mikepaul

    mikepaul Senior Member

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    http://www.priuschat.com/forums/download.php?id=210 doesn't show how the sender for the gauge is implemented.

    If it's a strain gauge, weighing the gas, then maybe that's the problem...
     
  18. jimvitz

    jimvitz Junior Member

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    OK, I'm not quite done with the present tank (just went to one bar blinking this morning), but here's some data on the progression of bars, mileage, and mpg for this tank.

    # of Bars - miles per bar - tank miles - displayed mpg

    9 - 76 - 76 - 61.4
    8 - 54 - 130 - 60.2
    7 - 43 - 173 - 59.0
    6 - 40 - 213 - 58.3
    5 - 44 - 257 - 58.1
    4 - 32 - 289 - 56.6
    3 - 26 - 315 - 55.6
    2 - 55 - 360 - 58.6
    1 - 10 - 370 - 56.5
    blinking - 35 - 405 - 57.4

    I'm now at 440 for the tank and will fill up later today. Interestingly, the 10 mile bar occurred over the wekend when the temp dropped to the low 40's with rain. My actual mpg has always been about 2 mpg less than the displayed. Maybe others could record similar data and see if a pattern emerges? Stay tuned.
     
  19. randalla

    randalla Member

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    I'm on my third tankful since picking up the car on March 30th. The first time I filled it up after the dealer tankful it took 9.5 gallons and gurgled and spit back about half a cup or so of gas after trickling in the final 2 gallons. On my most current fillup, I went 565 miles on 10.5 gallons riding on the final non-blinking square of the gas guage rendering 53.0 mpg on the MFD. I filled up before the blinking started because by calculating my mileage from the total miles driven it was starting to make me a bit nervous not knowing when the blinking would start and how much reserve would remain. During the final trickling in of fuel, the gurgling started, so I stopped the pump and the gurgling stopped. I then I trickled in a bit more and the gurgling started and again stopped when I stopped the pump. At this point I was at 10.5 gallons and decided to stop filling. As soon as I pulled out the pump handle, the gurgling started up and once again about a half cup of so of gas spurted out of the filler pipe. :pukeright: There seems to be a correlation between the pressure backup and release when the pump is removed. BTW, the air temperature was about 65 and dry.
     
  20. seeh2o

    seeh2o Prius OG

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    It's more like...that d*mn guess gauge. 350 miles, 47+ mpg and the blinking light comes on. :cussing: I knew that couldn't be right as I've driven it 450+ miles at nearly the same mpg. I drove another 45 miles, to 395 and decided to "fill it up". I only got 8.5 gallons in it - and that was pushing it. :Wth:

    I really hope Toyota gets a fix for this. Someone coined the phrase "guess gauge" they were dead on. :roll:
     
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