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First Mile mpg

Discussion in 'Gen 2 Prius Fuel Economy' started by gazz, Jan 3, 2008.

  1. gazz

    gazz Member

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    A recent post in which Bob Wilson stated that using "N" during the very initial warm up phase as beneficial to cold start mpg got me thinking. So the last two mornings I have used this method, what I can do is accelerate from a cold start to 30mph and then drop it straight into "N" and glide to the junction at the end of my road. What I noticed is that normally I get about 20mpg while driving very carefully during this period, but in "N" it gets 40-50mpg, and my first 5 mins nearly matched my summer mpg.

    Out of all the things I've tried during cold driving this has made the biggest difference.

    Any thoughts.
     
  2. JimboK

    JimboK One owner, low mileage

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    I do the same thing, terrain allowing, until I get to S2 and can force shutoff with the EV button.

    I moved a couple of months ago, and the road through my new development is ideal for this: a gradual downhill for about 1/3 mile. It's lightly traveled, so I accelerate only to about 20 MPH before putting it N. That's normally enough for momentum to carry me to the stop sign.

    It's especially helpful given that I can't plug in the block heater at my new place. :(
     
  3. gazz

    gazz Member

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    Yes I use a block heater to. Only need to coast a few hundred yards but seems to get you into S2 and the engine will shut off on its own.

    You state you use the EV button to force a shutdown, will it not shutdown on its own once that initial stage has taken place. (ign no longer negative).
     
  4. JimboK

    JimboK One owner, low mileage

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    It will if the car's at idle, but not while trying to glide until S3/S4 (ICE temp 70C) is reached.
     
  5. bstanier

    bstanier New Member

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    My feeling is that using N in this way delays recharging the HV battery while the ICE is operating at low efficiency. This will have to be done later, and then the ICE may be operating more efficiently so perhaps there is an overall gain. But don't take too much notice of the first 5 minute bar. Its the long term figure that matters.
     
  6. JimboK

    JimboK One owner, low mileage

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    There is no recharging of the battery during S1 anyway. The electric motor propels the car while the ICE's total focus is on warming itself and the catalytic converter. So running in neutral during this stage is to minimize battery discharge.
     
  7. gazz

    gazz Member

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    I wounder if that is a difference in UK spec, I can glide with engine off at S2, as soon as ign goes positive about 1/2 mile normally about 40C but I think it is more time based. Over 70C I have to go over about 35mph unless it goes into S4.
     
  8. JimboK

    JimboK One owner, low mileage

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    Hmm, could be. In fact, it must be, if that's how yours behaves. Seems odd that while an S3 glide from speeds <35 MPH is prevented (same as the US version), yours allows it in S2. Another of the great engineering mysteries of the car. :confused:
     
  9. gazz

    gazz Member

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    Must make it interesting for you in the cold, with temp down to freezing if I use my heater it can take miles to reach 70C but luckily I can still ICE off glide. One option is in fact is to use the heater to keep it below 70C but above 60C and it will ICE off at any speed. (not easy but in low speed situation can be of benefit)
     
  10. JimboK

    JimboK One owner, low mileage

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    Yep, that's why I use the EV switch pretty frequently during warmup in this cold weather. And I keep the heater off as much as I can tolerate so I get it up to full operating temp ASAP.

    You Brits sure do things wacky! :D
     
  11. gazz

    gazz Member

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