Low Speed, Low MPG

Discussion in 'Gen 3 Prius Fuel Economy' started by Sarp1028, Oct 30, 2015.

  1. Sarp1028

    Sarp1028 Junior Member

    Oct 14, 2015
    2012 Prius
    After a fair amount of time of due diligence reading the forums I believe my scenario is a unique topic to the forums.

    My driving profile is essentially that of an ice cream truck- that is my average speed is ~11 MPH.

    My current MPG result is ~33 MPG

    Many data junkies have done a great job plotting speed vs mpg with many other factors in between. Unfortunately this work does not accurately reflect my situation considering the cars are still warming up in this MPH range before the user collects data on the speeds of concern... namely highway speeds.

    Do my results appear to be consistent with my driving profile?

    Tires are all inflated to 51psi in accordance with the manufacturer: Sumitomo HTR A/S P01 195/65R15

    Temperature range is between 55F to 75F

    Thanks for any input!
  2. tanglefoot

    tanglefoot Whee!

    Mar 27, 2007
    2007 Prius
    Yes, it is difficult to obtain high fuel economy averages at low speeds unless electric glide is used. Whenever the engine is running at all while the car is traveling at low speed, instantaneous fuel economy will be quite low (often >20 mpg).

    For ice-cream-truck like driving, the best bet is likely to drive at higher speeds for at least 10 minutes to get the hybrid system into its later warm-up stages (do you have to get somewhere first, before driving slowly?). Then, engine-off electric glide is more likely to be used for low-speed driving, greatly increasing average fuel economy.

    To help the system stay in electric glide, try to use light pedal pressure and minimize the use of the climate control system and other accessories. The engine will run at times, but on level ground, once the system is warmed-up, it should be possible to use electric glide for the majority of the time. For ascents and significant acceleration need, apply additional pedal pressure to use the gasoline engine direct-drive. Once on the flats again at low speeds, lift off the pedal and when the gasoline engine stops (instantaneous mpg bar goes to the top), then feather the throttle pedal and try to stay in electric drive (infinite mpg) for longer periods. It works better in warmer temperatures.

    Oh, this is a Gen 3--you have an EV button, don't you? Strategic use of the EV button can also help. In the long run, it may be better to learn to use electric glide without the EV button, as to not stress the system too much.
    #2 tanglefoot, Oct 30, 2015
    Last edited: Oct 30, 2015
  3. bisco

    bisco cookie crumbler

    May 11, 2005
    2012 Prius Plug-in
    Plug-in Base
    sounds right to me. look on the bright side, another vehicle would probably return 15 mpg under those conditions.

    have you ever considered going for a regular drive to see what kind of mpg's you can obtain?
  4. Mendel Leisk

    Mendel Leisk Patron saint of newly poured sidewalks

    Oct 17, 2010
    Greater Vancouver, British Columbia, Canada
    2010 Prius
    Pretty much off-topic, but that's kinda over the top. The tire manufacturer more likely says to set tire pressures according to the guidance of the car manufacturer. The number embossed on the tire's sidewall is the max pressure and max load specification. It's by no means recommended.

    That said, a few people use that. A lot more go with what's on the decal in the driver's door jamb. And a few, and I'm in that camp, just raise them a bit.
  5. bwilson4web

    bwilson4web BMW i3 and Model 3

    Nov 25, 2005
    Huntsville AL
    2017 Prius Prime
    Prime Plus
    I concur with the earlier suggestions:
    Mail delivery?

    Are you under any particular order or time constraints?

    If you have the option of changing the order of a regular route, use Google Map/Google Earth, and plot your existing route. Then use the topographical view. Try to always start at the highest point of a section and descend in altitude as slowly as possible. This may add non-delivery 'climb' segments. Gravity will be your friend on the descents maximizing engine off time.

    Consider getting a Garmin Nuvi type GPS because it will record the route including altitude changes. These can be combined with Google Earth to see the altitude and route AFTER a delivery series.

    Also, consider getting a Scanguage II configured to monitor engine rpm. When climbing, as much as possible keep the engine rpm under or around 3,200 rpm. This is the maximum cooled, EGR flow, the highest power in maximum efficiency mode.

    I would also recommend getting the transaxle oil changed and taking a clean, dry, water bottle to get a sample. Testing is optional but I suspect you be 'surprised.' This won't be a magic bullet but it will help reduce transaxle losses.

    At temperatures under 75 F, consider a conformal, full, lower bumper inlet block. Initially test with duct-tape, cardboard box. A fairly small opening for let some air in can be left. You might consider the 2015 Prius grill block as a Toyota engineered solution.

    Bob Wilson
    #5 bwilson4web, Oct 31, 2015
    Last edited: Oct 31, 2015