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New owner with MPG questions

Discussion in 'Gen 2 Prius Fuel Economy' started by TNPrius1, Nov 16, 2005.

  1. TNPrius1

    TNPrius1 New Member

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    My wife and I finally got our new Prius 2 1/2 weeks ago. We have almost 600 miles on the car and we are starting to learn how to "tweak" the throttle while driving to get the electric motor to come on or the ICE to shut down or both.

    My wife is the primary driver and has been averaging (according to the MFD) around 43 MPG or so). When I drive (weekends) the average milage tends to increase by several MPG (depending upon the distance I drive).

    This past weekend we went on a short trip to a town about 50 miles away. I wanted to get a more accurate average of the MPG I got on this trip so I reset the average and made the trip. With 4 people in the car the MFD claimed that I averaged 53.4 MPG to our destination, mostly interstate. Before returning home, I again reset the average and got 54.7 on the return trip- with four people in the car.

    Is this possible? I don't see people posting MPGs like this in the forums and it just seems too unreal to believe. So I wonder, how accurate is this? Can this be trused to be reasonably accurate over a short 50 mile trip?
     
    #1 TNPrius1, Nov 16, 2005
  2. Tideland Prius

    Tideland Prius Moderator of the North
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    This is because you've resetted it. Our mileage are per tank mileage so it's averaged over the entire tank from fill up to fill up.

    You can get an average of 60 or 70mpg if most of the way home was, say downhill.

    The MFD is fairly accurate (I think it was ±1 or 2 mpg).
     
    #2 Tideland Prius, Nov 16, 2005
  3. Jack 06

    Jack 06 New Member

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    Sure, it's possible! You must've driven the speed limit or less.

    More accurate to refill at the pump each time, even though the cashier might grimace when you buy $2 worth. Or carry 1-2 1-gal. gas containers with you.

    Your display can't be off that much, as Tideland Prius says.
     
    #3 Jack 06, Nov 16, 2005
  4. BrianTheDog

    BrianTheDog New Member

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    What was the terrain like? Was it warmer weather than the previous weeks, like it was here? These are both contributing factors.

    I also noticed a slight increase in my MPG after the first few hundred miles, which I attribute to learning the car and breaking in the engine.
     
    #4 BrianTheDog, Nov 16, 2005
  5. tomdeimos

    tomdeimos New Member

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    I regularly take trips with over 55 mpg. Much nicer than reading my low tank mpg from my short work commute!

    I measured for tankfulls till I had lots of data to prove my mfd was accurate to better than 1%. Now I reset for each trip, and find it makes improving technique much easier, since you get more instant feedback, without the wild variations on the instant mpg.

    Every post I've read where people checked their mfd accuracy showed it to be typically within 2%.

    The car can get great trip mpg. I've maxed out at over 70 mpg, by driving slow.
    The places you lose is in stop and go traffic, and warm ups on short trips, or too much AC or heater loads.
     
    #5 tomdeimos, Nov 16, 2005
  6. JCox

    JCox New Member

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    Question then. Based on Tidelands response, let me run this by you guys and let me know what you think.

    I have had my 05 for going on two weeks. 5 days after I got it, I drove from Winston-Salem NC to near Greenville, SC. On the way down, I had to put gas it due to my not having but half a tank when I left. I filled up and reset the trip odometer. We drove down there, drove home and then Sunday morning, I filled back up. I had driven 285 miles before I filled back up. I only put right at 5 gals of gas. I belive it was 4.89 gallons. I figured that up and got right at 51mpg but the MFD showed 43mpg.

    Any comments/suggestions???
     
    #6 JCox, Nov 17, 2005
  7. Maytrix

    Maytrix Member

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    I've found the MFD is fairly accurate. I've been keeping track of both calculated mileage and MFD since day 1 and if I average both out, they are very close to each other (within 1mpg).

    Getting 51 on the MFD and 43 when filling up is not at all unusual. The tank doesn't fill up exactly the same every time, so while you might use 5 gallons of gas on a trip, you may only be able to get 4 gallons in (making your calculated milage higher). Although on another trip, you might be able to put in 6 gallons, making your calculated milage lower.

    Try keeping track of both over a period of time - I think you'll see the results line up with each other.
     
    #7 Maytrix, Nov 17, 2005
  8. Tideland Prius

    Tideland Prius Moderator of the North
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    mmhmm. If you fill up and the calculated is much higher than the MFD, I'd say the pump cut off too early. Now you might say that I'm trying to avoid the subject but I'm serious on this one. I just checked my spreadsheet and most of the time, my MFD average was more optimistic. Over nearly 20,000kms, my MFD average is 4.94L/100km and my Calc'd average is 5.16L/100km. The MFD is ~4% off (~2mpg off). Also, what accounts for the my calc'd being higher is that I don't stop at the first auto shut off at the pump.


    So, average it over several tanks first. I realise the change in weather will make it hard since the bladder shrinks as the temperature drop so you'll be adding less and less fuel making it seem like you're getting better mileage than what the MFD says. Keep a spreadsheet or something. I'm a new owner myself having the car for just over a year and looking back, for the first two months, my calc'd average was waaay off from the MFD.
     
    #8 Tideland Prius, Nov 17, 2005
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