Cruising range disparity?

Discussion in 'Prius c Fuel Economy' started by cutter44, Apr 29, 2015.

  1. cutter44

    cutter44 Member

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    Hi all.

    I filled up this morning for the first time since picking up the car last Saturday. Cruising range display was showing I had only about 78 miles left and I have a 40 mile commute. The gas gauge showed about one bar below the halfway mark, but I didn't want to take any chances. So I filled the tank...even squeezing a few extra clicks to round up to even cents. I get in the car and now it's showing a cruising range of 340 miles or something like that (I forget exactly, but it was definitely below 400). Meanwhile, my display has been showing I'm getting anywhere from low 50s to as high as 61 mpg during my commute this week. I did the actual math after the fill-up and I had gone 305.3 miles and filled up with 6.246 gallons, for a calculated mpg of 48.9.

    Is this just a matter of a miscalculating display? Mind you, I'm not complaining about 48.9 mpg. I'm still getting used to this car. But if that's the rate, and the tank holds 9.5 gallons, shouldn't my cruising range with a full tank show at least 440 miles? I was kind of looking forward to filling up once a week.

    And here's a thought. It took 6 gallons, which means I had at least 3 remaining. Even at a conservative 40 mpg, it should have calculated cruising range to be at least 120 miles. But it was showing 78.

    Any thoughts? Is something amiss or is this just the way it is? Thanks.
     
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  2. fuzzy1

    fuzzy1 Senior Member

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    In order to keep customers from angrily blaming the car maker when (not if) they run out of gas (But the meter said it had enough range!), a significant portion of the fuel tank is set aside as safety margin or reserve, and not counted towards that range.

    Actual fuel consumption and range is very highly variable, depending on many changing conditions that the car cannot possibly forecast, and many customers simply don't understand or cannot be expected to accurately compute. Thus, to manage customer expectations, or at least keep them from blaming Toyota when they end up running out of fuel, a couple spare gallons are set aside and not shown on the fuel gauge and distance-to-empty estimate.

    My Subaru Forester takes a different approach. Its distance-to-empty gauge is actually fairly accurate. But it also has more in-your-face warnings that fuel is getting low -- a chime and TWO dashboard warning lights in bright warning colors when about 3 gallons are left, a fuel gauge whose bottom bar actually goes blank with about 2 gallons left, and a distance-to-empty display that goes blank with about 1 gallon left. And its distance gauge is always rounded to the nearest 10 miles, not 1 mile, so it is always more vague than the Prius distance display.
     
    #2 fuzzy1, Apr 29, 2015
    Last edited: Apr 29, 2015
  3. cutter44

    cutter44 Member

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    Okay, I'll buy that. Just curious. If I had continued on an additional 100 miles, let's say, what would the cruising range display show? Does it stop at 0 or does it go into negative numbers to make its point?

    Funny you mention a Forester. That's what I traded in for the Prius. I knew that if my low fuel light came on in the Forester, I still had a couple of gallons before actually running out. Of course, that couple of gallons would get me maybe 50 miles.

    Thanks for the info.
     
  4. fuzzy1

    fuzzy1 Senior Member

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    It stops at 0, at least in my Liftback. That is the very last warning. I haven't heard of other models being any different.
    My 2014 Forester's DTE behaves much different than the Prius DTE. In addition to using the whole tank, the Forester forecasts based on the mpg from only the last 30-ish miles. Its estimate can climb enormously when conditions improve. I've seen it increase by more than 100 miles in the first hour after filling up, even as a couple gallons are burned off. Of course, it can also drop very rapidly when climbing into the mountains.

    In contrast, the Prius DTE climbs only at fillup time. Between fillups, it never increases. Its estimate is based upon a much longer mpg history. It will also fall quickly when climbing into the mountains, though not as rapidly as the Forester. But on the downhill, it never increases. In fact, even when gliding downhill with no fuel burn at all (even regenerating and filling the battery), it still decreases at least 1 mile for every 2 miles driven. On long descents, this can cause it to reach 0 prematurely. It will also snap to 0 from somewhere around 5-ish miles remaining on flat roads, or even from 10-ish miles when climbing a hill.

    For how much fuel actually remains in a Liftback, read the first post of this thread: [WARNING] Running out of gas (Gen III) | PriusChat
    Your 'c' will be somewhat different, but I'm not aware than anyone has run the same detailed experiments with it.

    Prior to this Forester, my previous Subaru, Honda, and last Ford all had at least 100 miles of range left when the fuel gauge reached 'E' or the low fuel warning lit up. But my first Ford was different, it actually ran dry with its fuel gauge still a bit above 'E'.
     
    #4 fuzzy1, Apr 30, 2015
    Last edited: Apr 30, 2015
  5. cutter44

    cutter44 Member

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    Just a little follow-up. Second fill up yesterday and I was a little more daring, waiting until I hit the magic 400+ miles on the trip odometer. So here's the result:

    • gas gauge light still showed two bars remaining (so no beep or flashing)
    • cruising range showed 16 miles
    • trip odometer showed 415 miles since last fill up
    • tank took 7.81 gallons (rounded up after second click-off)

    I'm pretty pleased with 53.2 mpg and a range of more than 400 miles on a tankful. And I think I probably could have gone another 40 miles or so before I dropped another light off the gas gauge. I may try to stretch it next time just so I have a point of reference and so I can actually see if I can hear the beep and see what the Cruising Range does after it goes to zero with fuel left in the tank. Based on the fact that it took under 8 gallons, I'm fairly comfortable that I had another gallon in there before hitting the danger zone. Although I don't intend to push it. Just curious.
     
  6. bisco

    bisco cookie crumbler

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    dye should hit zero when your last bar flashes. seems low for two bars.
     
  7. cutter44

    cutter44 Member

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    And here's another follow-up. I managed to get a week's worth of commuting out of this last tankful. This time I wanted to try to push it a little to see just what the numbers and gauges mean, so I waited...and waited...before filling up today. The gas gauge/meter had been showing two bars and the Cruising range had been at 1 mile since yesterday afternoon. Today I paid close attention as I was driving around running errands, as I was watching for the blinking single light on the meter.

    Well, as soon as the Cruising Range hit 0, the gauge went to one light and it began blinking. I drove about another 1.2 miles to the gas station and filled her up. I rounded up after the first click-off and I had pumped in 8.279 gallons, so I guess I had a little more than a gallon left. Conveniently, that equates in my mind to the one bar on the meter. I had driven 488.7 miles, for a real average of 59.0 mpg. I had been hoping to get 400+ miles out of a tankful. I know it may not always be this way, but it's great knowing I can commute for a week on one tank of gas. To say I'm very pleased is an understatement. Yes, it would be nice if it were a 12-13 gallon tank, but I can live with this.

    Just thought I'd share.
     
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  8. Mo G

    Mo G Member

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    I usually reset trip A counter, and take a picture of the Range to empty , after every fill up, to see if my C is lying to me. It usually is by 20-40 miles. It tells me range of ~ 360-380, I get around ~380-400. The pump clicks off around 8.2 ish if I fill up as soon as it beeps. Or I'll drive another 15-20 miles and hit 400 for the tank, and hope to god it doesn't run out of gas, ever again. Lucky enough, if you run out of gas, and the battery is full, it will run in EV mode for about 1.5 miles, dependent on speed and acceleration. It will get up to 42 MPH.
     
  9. ufourya

    ufourya We the People

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    I know reading the manual is a drag, and I do not claim to have read it all. Somewhere in it is the statement that when cruising range hits 0, there is approximately 1.3 gallons in reserve. This comports with your later findings.

    After you fill up, the cruising range is based largely on the mpg you got on the previous tank. I have not determined the 'formula' the computer uses to arrive at this number. I HAVE kept track, to a large extent, of the cruising range before and after filling up in my notes at fuelly.com beginning with fill-up 190 in Nov. of 2014. Before that I did keep track of cruising range after filling up beginning around fill-up 97..

    If there is an interested reader with a mathematical bent who wants to tackle figuring out what the computer does, I think my information is available to the public at fuelly. The number in () is the cruising range before filling up.
     
    #9 ufourya, Jul 27, 2015
    Last edited: Jul 28, 2015
  10. HybridHipster

    HybridHipster Junior Member

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    Way I see it -- it's true: there's no time left to "cruise" -- at this point, one's neck is sore from looking for a gas station sign. Hardly cruising around. ;-)
     
  11. HybridHipster

    HybridHipster Junior Member

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    This is what my manual says:

    "Low fuel level warning light
    Remaining fuel is low

    When the remaining fuel is approximately 1.3 gal. (5.0 L,
    1.1 Imp. gal.) or less, a buzzer sounds and comes on
    * Refuel the vehicle."

    What this tells me is that in theory, whatever the remaining cruising distance might read: at 5.0L/100K, when the buzzer sounds, I have "about" 100 km to run dry, for some value of 100 km.
     
  12. carolD

    carolD Junior Member

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    Hi
    i am new here. I have a 2015 Prius c2. I am averaging about 44 mpg. I am using Eco mode. Do you feel it is saving gas. I am only getting around 325 miles a tank full. Is that good? I'm just curious. I love the car. Most of my driving is city. Any help would be appreciated.
     
  13. ufourya

    ufourya We the People

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    I see you have asked a few questions in various threads, and have learned, no doubt, about proper tire pressure, the size of the tank, how much fuel is still in the tank when the last bar starts blinking, ambient temperature, terrain, etc.

    If you have not already watched this video, it has some good information on the basics of good prius driving. It's a regular hatchback, but the principles still apply:

     
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