Guess Gauge Pip Consistency

Discussion in 'Gen 2 Prius Fuel Economy' started by NC_Prius, Nov 3, 2008.

  1. NC_Prius

    NC_Prius Member

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    After reading about the apparent inconsistencies of the guess gauge, I have actually found mine to be fairly reliable after monitoring it for the past 6-7 tanks (at least if you fill the tank each time). However, I drive the same route on a daily basis and achieve the same average mpgs per tank (approx 54-55 mpg average on the computer). Here is what I have found:

    Pip 10 disappears at 110-130 miles (depending on how full the bladder)
    Pip 9 disappears at 30 addl miles
    Pip 8 disappears at 30 addl miles
    Pip 7 disappears at 30 addl miles
    Pip 6 disappears at 30 addl miles
    Pip 5 disappears at 40 addl miles
    Pip 4 disappears at 55 addl miles

    I have not been able to check the consistency after pip 3 disappears because I typically fill the tank on the weekends with 2-3 left.

    If there's any variation in my average mpg's, there may be a few more or less miles per pip, but they are always very close since my average mpg is fairly constant.
     
  2. JimN

    JimN Let the games begin!

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    Are the temps relatively constant?
     
  3. NC_Prius

    NC_Prius Member

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    Yes, the temps were fairly consistent. During the few colder days we had last week the pips disappeared a few miles earlier than usual, as would be expected. Of course, by the same token, the avg mpg was slightly affected as well. Obviously, as it gets colder the avg mpg and miles per pip will drop. Still, I'm surprised that the pip count per miles is reasonably predictable, so the gauge is not that unreliable, at least starting with a full tank.
     
  4. rkskeet

    rkskeet New Member

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    NC Prius - I agree that the pips are consistent. My Pri reacts pretty much as you describe the way yours performs..
     
  5. Fraser

    Fraser New Member

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    I have found similar f10th-pip results as OP. Pips drop at more like 35-40, although mpg average is a couple mpg less than OP's. I don't see as much variation from 30 on pips 4 and 5, seems to be more consistently in the 35-40 range down to second pip, which is where I normally fill.
     
  6. toxicity

    toxicity A/C Hog

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    Did you have consistent driving styles? One time I went on a 300 mile all-highway trip, and did it in the middle of the night so I could drive how I wanted; I set it to cruise at 55mph. From a fully filled tank before leaving, the first pip went out at 187 miles. The next one went out within 20 additional miles...

    Then on another fill up, I drove really aggressively in the city and the first pip disappeared after about 30 miles.
     
  7. mingoglia

    mingoglia Member

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    I've found the gauge is pretty consistent in the cooler temps. In AZ, when it's in the 108-110 degree range it's very temperamental. I don't know if the bladder is just over-stretched or what... but when the last pip starts blinking in the summer it's almost too late to pull over at the next intersection and get fuel. In the cooler temps I can drive 50+ miles once the pip starts flashing and still have a gallon of fuel in the car.
     
  8. Brodie

    Brodie New Member

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    My Prius also seems to be pretty consistent, but that first (or 10th?) pip definitely varies a lot depending on how full the fillup was. I've gotten as little as 50 miles and as much as 120 miles on it.
     
  9. NC_Prius

    NC_Prius Member

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    For my most recent tank, the pips followed the same expected pattern, but this time I filled up with just one pip left. So I have a one-time report for when Pips 3 & 2 disappeared:

    Pip 3 disappeared at 50 addl miles
    Pip 2 disappeared at 70 addl miles!


    The mileage was as follows:

    Pip 10 disappeared at ~ 110 miles
    Pip 9 disappeared at ~ 30 addl miles (140)
    Pip 8 disappeared at ~ 30 addl miles (170)
    Pip 7 disappeared at ~ 30 addl miles (200)
    Pip 6 disappeared at ~ 30 addl miles (230)
    Pip 5 disappeared at ~ 40 addl miles (270)
    Pip 4 disappeared at ~ 55 addl miles (325)
    Pip 3 disappeared at ~ 50 addl miles (375)
    Pip 2 disappeared at ~ 70 addl miles (447 on fillup -- 8.55 gallons for an avg 52.3 mpg. Computer registered 54.7 mpg)


    So the top half of the gauge is heavy-weighted towards the first pip (on a true fill-up) with the rest of the pips registering consistent mileage. Whereas the bottom half slowly increases in mileage per pip (with the exception of pip 4 and 3 -- and pip 1 is unknown in my observations). And I pretty much see the same thing on each tank. The only variance being a few mpg's up or down depending on my overall average.

    Of course, those getting significantly more or less overall average mpg will see a larger difference on the per-pip basis.
     
  10. nooaah

    nooaah New Member

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    On my last tank I was down 3 pips before I even got to 100 miles. Down to 2 pips before I got to 300.
     
  11. NC_Prius

    NC_Prius Member

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    I've had it happen where I could not fill the tank bladder completely. That affects how many miles you will go before that first (tenth) pip disappears, and subsequently, the total amount of mileage you will get on the tank because it's not full. And yet, there is still a measure of consistency with the pips. For example, in your case:

    Pip 10 disappeared at ~ 30 miles? (Just guessing at the mileage point)
    Pip 9 disappeared at ~ 30 addl miles (60)
    Pip 8 disappeared at ~ 30 addl miles (90)
    (3 gone and not yet at 100 miles)
    Pip 7 disappeared at ~ 30 addl miles (120)
    Pip 6 disappeared at ~ 30 addl miles (150)
    Pip 5 disappeared at ~ 40 addl miles (190)
    Pip 4 disappeared at ~ 55 addl miles (245)
    Pip 3 disappeared at ~ 50 addl miles (295)
    Down to 2 pips at 295 miles.


    However, on my current tank, for the first time I saw 40 miles on the second (ninth) pip without an increase in my average mpg. It also happens that I didn't get a full bladder of fuel on fillup because the tenth pip disappeared at 80 miles. But the rest of the pips have followed the pattern above, and I am now seeing 35-45 degree weather. The colder weather may account for why I was unable to completely fill the bladder.
     
  12. nooaah

    nooaah New Member

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    Well, somehow my new tank is hitting 50.5 MPG after the first 150 miles in 32 degree or below cold. Grills still not blocked, but I did inflate my tires. turns out they deflated to 32 since last month. I have 5 pips left after 150 miles. I was able to put in 6.8 gallons after 300 miles on my last tank with mid-upper 40's MPG.
     
  13. elcorazon

    elcorazon New Member

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    my results are similar only much worse. my first pip tends to disappear around 50-60 miles, then I get between 20-35 miles for the next 5 or 6 pips, then get around 35-50 for the last couple of pips. I just had to fill up as my last pip was blinking at 322 miles. Took 8.47 gallons to fillup. Screen said I was getting 39.5 for the tank.

    I hate winter.
     
  14. KAR IDEA

    KAR IDEA Member

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    this is about the same for me. 70 to 80 miles before the first pip goes "see ya" in 30 degree weather. However yesterday, inexplicably, we had 120 miles on the first pip, then get this...we lost two more pips in less than 15 minutes!!! :crazy: Thas' crazy man...

    I agree winter is the pits...
     
  15. elcorazon

    elcorazon New Member

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    my current tank lost pip #1 at 30 miles and has already lost 4 pips at 100 miles. my screen has me at 34.5 mpg so far for the tank. grills are blocked at the moment. I may block more though. need to pick up more insulation.
     
  16. M8s

    M8s Retired and Lovin' It

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    I go about 105 miles on the first pip and then 30 to 35 on each pip thereafter.

    I've got a theory that would explain this inconsistency. Maybe it takes a while to cancel the first pip because of the the gas in the filler pipe. Even though the ICE is running, the tank remains full until that amount of gas is burned. Only then does the tank-mounted gas gauge begin to show usage.

    Sound plausible? If so, does the filler pipe hold about 1 gallon of gas?
     
  17. PaulHS

    PaulHS Member

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    So much depends on the ambient temperature and your current FE. During the summer, I was seeing between 200 and 265 miles before the first pip dropped. Now, with temps of 26 to 45 degrees F, I'm getting 30 to 40 miles.

    I seriously doubt it. The attached document is very helpful for a number of reasons. Check out Figure 3.10. I'd be surprised if the filler tube held a quart.
     

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  18. qbee42

    qbee42 My other car is a boat

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    Not really. By their very nature, the fuel gauges in automobiles are not very precise. The error is normally designed into the upper end of the fuel gauge, as it is more important to know when you are about to run out of fuel than to know exactly when you have a full tank. That said, it is true that the fuel gauge has no way to detect fuel above the maximum reading, so extra fuel in the filler pipe will extend the time that the gauge shows full.

    Tom
     
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