Not Complaining, but want to understand better...

Discussion in 'Gen 2 Prius Fuel Economy' started by Mellowman, Sep 17, 2013.

  1. Mellowman

    Mellowman Junior Member

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    Yes, I've only got a few tanks under my belt on my 05' but I'm curious on the mpgs I've been getting. Went on a road trip where it was mostly highway 65-70mph and got about 51-52 mpg. When I calculated by miles between filling tanks I got about 5 mpgs less (46mpg).

    Then had a tank that was mostly around the city, short trips, relatively flat, and got computer reading of 46 mpg. While I'm super pleased with these numbers (even if they may be skewed a little higher) I just thought I should expect higher city mileage and lower highway mileage.

    I know the original tires aren't on my car, they are Michelin's but I don't know which kind.
     
  2. xpcman

    xpcman Senior Member

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    Short trips result in gas being burned to heat the engine/exhaust to a point where the engine has minimal pollution.

    If you do nothing but short trips then expect MPG in the low 40's.

    Once winter comes you will see another few mpg lost to heating the inside of the car.
     
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  3. dorunron

    dorunron Senior Member

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    EPA estimate on the Gen II is as follows

    48 City
    45 Highway

    YMMV

    What you are posting and seeing is normal. If you want to get superior mileage, learn about hypermiling. There are links in my signature that explains that.

    Best of luck to you.
     
  4. sportcoupe

    sportcoupe Junior Member

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    You have a variable capacity bladder fuel tank. You cannot accurately calculate mpg by gallons added and miles traveled. We must rely on the trip computer for mph.
     
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  5. dorunron

    dorunron Senior Member

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    It seems that the onboard computer is a little over what actual mileage is. Most folks who drive a Prius calculate their overall mileage over several tanks of fuel since one tank will not give accurate figures due to the bladder. You might consider averaging a minimum of five tanks of fuel together to get a good basis of miles per gallon. Fuelly.com is a excellent site that can be used for just that purpose.
     
  6. Shipscarver

    Shipscarver Junior Member

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    I am getting about 32 MPG, with a combination of expressway and local driving. What am I doing wrong?
     
  7. fuzzy1

    fuzzy1 Senior Member

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  8. Tideland Prius

    Tideland Prius Moderator of the North
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    Well there are many possible reasons.

    • Accelerate smoothly. Don’t accelerate hard
    • Reduce the amount of braking - if you can coast or glide to maintain momentum, all the better
    • If you have to brake, brake gently to maximise regenerative braking. Harder braking will engage the brake pads
    • Check your tire pressure. Underinflated tyres increase fuel economy by 10%
    • Check your wheel alignment
    • Ensure that the oil isn’t overfilled (check the dipstick)
    • Check the tire type. A low rolling resistant tyre can help improve fuel economy
    • Drive with the shifter in “D” not “B”. B does not let the engine shut off when stopped so it will continue to idle
    • Reduce the load on the climate control - that means choosing a higher temperature in the summer and a lower one in the winter to reduce electricity consumption by the A/C compressor or the PTC heater. It’ll also reduce engine idling in cooler temperatures to run the heater
    • Drive at a slower speed. 70-80mph will significantly increase fuel consumption compared to 50-60mph.
     
  9. Shipscarver

    Shipscarver Junior Member

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    How old is your 12v battery? What is the voltage reading of your 12v battery after sitting over night? (Method Here)
    1 1/2 yr old 12V battery, It usually shows 2-3 bars t start.

    Have you had your alignment checked? Any pulling or abnormal tire wear?
    Yes - It has been maintained by AutoNation Toyota for the last 5 years.

    - Are you using the factory tires and wheels? If not, please indicate tire make, model and size
    Yes

    - What are your tire pressures?
    Factory standard, checked every 2-3 weeks at full service station. Dash warning for tires has never turned on.

    - Make, model, year, engine and transmission of previous car? (e.g. 08 Honda Civic Si 2.0L 4 cylinder, manual transmission) What did you actually get on the same trips/commute? (Please give us actual numbers, not EPA ratings.)
    2005 Kia Sedona, 14 - 17

    - How are you trying to drive (e.g. trying to stay in electric only?) and how hard are you braking?
    No and usually coast before braking

    - Are you "warming up" the ICE (internal combustion engine) by letting it idle after powering on?
    No

    - Are you driving using D or B mode?
    D

    - HVAC settings? Are you using the heater, AC, auto mode, etc.? If using auto, what temp is it set to?
    72 autoset

    - If reporting a mileage drop, did anything significant change on your car (e.g. accident, hit a curb or big pothole throwing off alignment, oil change/other maintenance/repairs, changed tires or wheels, etc.) or your commute?
    No major drop, it has averaged 34-38 for 3 years.

    - What fuel economy are you getting and how are you determining fuel economy? (trip computer or manual calculations)
    Info screen. Most recent - 178 miles @36.5
    mpg- What fuel economy are you expecting and why?
    42 seems normal

    - What are the approximate outside air temps?
    80-92

    - How long are your trips?
    1 mile, 5 miles, and 30 miles each way.

    - How much of it is city vs. highway? Roughly what's the average speed in overall and of each segment? Is there a lot of stop and go driving?
    40 - 60 trips of 1-5 miles city driving, and 6-10 round trips 60-70 miles at 75 MP expressway driving

    - What region/state are you in? (if you haven't set your location in your profile)
    Central Florida Gulf Coast

    - What's the terrain like of your drives? (e.g. flat, gentle hills, steep hills, etc.)
    flat

    - Is your oil overfilled? (i.e. above the full mark on the dipstick)
    no
     
    #9 Shipscarver, Sep 7, 2019
    Last edited by a moderator: Sep 7, 2019
  10. Shipscarver

    Shipscarver Junior Member

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    Much of my driving is expressway at 70-75 MPH.
     
  11. fuzzy1

    fuzzy1 Senior Member

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    Here are my initial thoughts. Hopefully several others will chime in too.
    Are you sure about the tires? A 2006 should not be on its factory tires anymore. They should have been replaced some years ago for age alone, no matter how few miles are on them. We'd like to know brand and model of what is installed now, lots of tires are not low-rolling-resistance.

    How many miles on the odometer?
    Are you checking while the tires are morning-cold, or after a highway run? Recommended pressures are for cold, not highway-warmed.

    This is worth getting your own pressure gauge, not depending on the unknown condition of a beat-up service station gauge. Many of them become inaccurate from use and abuse, though home gauges are known to be off too.

    Also, we like to see you quote actual pressure numbers, not merely say 'Factory standard'. This will catch a few misunderstandings.
    But has dropped to 32 now?
    Neither of those types will get great MPG.

    Those 1 and 5 miles trips on a cold engine and hot passenger cabin will clobber mpg in any car (except non-plugins), and there is little you can do about it. The 1s are particularly bad, because you have to (partially at least) warm the engine and cool much of the cabin, using a good bit of fuel without driving any real distance. This drags down the average.

    For the 75 MPH trips, take a look at this Gen3 chart, then subtract 5-ish mpg for being a less efficient Gen2, then subtract several more for your heavy AC use. Though that still ought to produce around 40, better than you are getting now.
    Updated MPG vs MPH chart | PriusChat

    It would be useful to learn what you get on a highway trip alone, without any of the short trips mixed in. Reset the Trip gauge when you start one of these trips, and tell us the resulting figure when you get back home.

    ----

    Additionally, do your wheel hubs get hot? This could indicate excessive brake drag.

    Resetting the Trip gauge before some of those short segments will also be instructive, highlighting the cold start (and hot cabin) penalty. The MPG should always start out horribly low, then climb the farther you drive. At 1 mile, it will still be horrid. By 5 miles, it ought to be climbing to a semi-decent number, but still not getting close to what the car can really do.
     
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