Miles Left Before Refueling

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by hoferchr, Jan 7, 2015.

  1. hoferchr

    hoferchr Junior Member

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    I live in Wisconsin, and it's been super cold here this week. I have a daily commute through town of about 7-8 miles...taking me about 15 minutes. This morning, I noticed that as I was making my way to work, the number of miles left until I needed to refuel was decreasing quickly. I had only gotten about 1.5 to 2 miles from my house, and the miles went from 46 down to 41 or 40. I'm wondering how this number is calculated? Is it averaging previous trips? Is it just because my gas engine is working harder during the winter and to also keep me warm? Should I be concerned? Would appreciate any insights to this oddity. Thanks.
     
  2. 2k1Toaster

    2k1Toaster Brand New Prius Batteries

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    You are probably asking for heat which means the engine has to run. If it is colder, it runs more. If it runs more, it consumes more petrol. If more of that gas is wasted just because the engine needs to spin to make you warm vs. propel the car, then you will get fewer miles out of the same amount fuel. It is averaging based off of past history as well as current information and with the current consumption being higher, the same volume of fuel will not get you the same distance.

    But in addition to the heat, when it is really cold everything from your tires to the road to what's on the road (snow/slush/etc) and even the density of the air all conspire against you.
     
  3. JimN

    JimN Let the games begin!

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    Should I be concerned?

    No. Situation normal. Pay no attention to MTE as it is an unreliable calculation. If you believe the numbers you'll be surprised how far you can go on zero miles.
     
  4. fuzzy1

    fuzzy1 Senior Member

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    Fuel consumption is not steady. It is very highly variable, depending on road and traffic conditions and weather and engine warmup cycles and speed and elevation changes and plenty more.

    But the computer that figures the miles remaining cannot possibly know all those factors into the future, so it must guess with a simplistic formula. It will often miss by a lot.

    In this case, your engine was burning a lot of fuel to warm up. If you had reset a Trip meter when you started the car, at the 1.5-2 miles where you noticed that the miles remaining had dropped significantly more, you would have also noticed that the Trip MPG was abysmally low, well below average, as it always is just a few miles after a cold start.

    Because of the considerable variability of fuel consumption, and to manage customer expectations, the miles remaining display leaves a considerable safety margin. For some idea how much, read the first post of: [WARNING] Running out of gas (Gen III).

    Don't overthink this. Your main concern is that it is about time to refill the tank.
     
  5. bisco

    bisco cookie crumbler

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    i never look at miles to empty. just my gas gauge and miles driven on that tank. no idea why, i'm sure it's there for a reason.
     
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  6. retired4999

    retired4999 Prius driver since 2005

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    Mine beeps, and now it is flashing at me? Do I need gas?! How far can I drive? My estimate says 23 miles to empty, how accurate is it?
     
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  7. bisco

    bisco cookie crumbler

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    just keep driving, it will let you know when you're out of gas. these new cars are smarter than we are, don't try to out think them, especially if your over 55, and the temp is under 55.
     
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  8. Mendel Leisk

    Mendel Leisk Sand Pounder

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    I never pay any attention to the miles left gauge. Any time the tank's less than half-full, if we happen to roll by my gas station of choice, I pull in, fill up.
     
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  9. Easy Rider 2

    Easy Rider 2 Senior Member

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    If that is "distance to empty", then you should be VERY concerned.........about your bad habit of letting the tank get that low. ;)

    The displayed number is just a rough estimate.
    There is no good reason to let it get that low......especially in a cold environment where and empty tank collects more condensation AND you might need the gas to survive should you run off the road and are trapped in freezing weather.

    Don't worry about it until the engine dies.
    Running out of gas in Wisconsin in the winter is an adventure. :whistle:
     
    #9 Easy Rider 2, Jan 9, 2015
    Last edited: Jan 9, 2015
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  10. Mendel Leisk

    Mendel Leisk Sand Pounder

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    I especially like this last bit. There is NO good reason to run the tank down, near empty. It's a pointless game.
     
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  11. DoubleDAZ

    DoubleDAZ Senior Member

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    I agree there is no reason to run the tank low, but the Prius generally still has almost 2 gallons left when the MTE reads 0 and the display starts flashing at about the 25/26 mile mark. Since I once had a display in our van read 1/4 tank when I ran out of gas, I generally stop for gas when the Prius gets down to about 2 bars, if not before. I do pay some attention to the mileage I'm getting and the miles I've driven in cases where I need to stretch it a bit because of distance between towns, like along I-10 in W Texas and New Mexico, and I glance at the MTE.

    I've also noticed that mileage varies a lot on trips, so if the MTE says 100 miles and I've been getting 50 mpg, I might think I can make 100 miles easily with 2 gallons to spare. However, if I suddenly encounter some hills, mileage can drop below 40 and I might need to stop sooner. A good example is Tucson to Monument Valley. I can get over 50 to Phoenix, but less than 40 up the hills to Flagstaff. Therefore, I might not make it to Kayenta, the last gas stop. So, I'd get gas in Flagstaff or Tuba City rather than risk it. I was getting over 50 in LA, so I thought it'd be no problem getting back to Phoenix on a single tank. Well, it wasn't, but my actual mileage was only 44 mpg and that was the closest I've come to putting 10 gallons in. Like I said, I knew I still had almost 2 gallons left, so I wasn't concerned, but what if the display had been wrong?

    It's not a problem around home where there are plenty of gas stations, but on trips I use Gas Buddy to fill up wherever gas is cheapest along my route. I stop every2 hours or so, so adding gas is not a big deal. Of course, I don't save much with current prices, but it's become a habit. :)
     
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