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From: liu on 13 Jun 2010 11:12
On Jun 12, 10:18 am, jim beam <m...(a)privacy.net> wrote:
> On 06/12/2010 06:51 AM, Don Stauffer wrote:
>
>
>
>
>
> > liu wrote:
> >> I'm trying some tips mentioned by these hyper-milers. One of them is
> >> to turn off the engine while approaching the intersection with traffic
> >> light on red. Sometimes due to the distance, I lost the power to
> >> brake. So I tried using the 2nd gear to slow down the car. (Note: I
> >> only do this with enough distance between cars, or I would rather
> >> turning the engine back on.) A few times I found the power gets back
> >> up again. Initially, I was wondering if I did turn off the engine and
> >> then realized that this is the same as push-jump start a car.
>
> >> So how does it work? Why would the engine start up again without
> >> involving the starter?
>
> >> Thanks,
>
> > If the car is in gear you are not really coasting. You need to keep on
> > the gas a longer distance before starting your deceleration, because the
> > car will decelerate at a higher rate when you are turning the engine
> > over. Therefore you are not saving as much gas as when you coast with
> > engine out of gear.
>
> > BTW, some of what hypermilers say works, other things do not work. Mixed
> > bag- depends on who says it. Coasting out of gear does work, playing
> > lights works even better (though playing and coasting are not mutually
> > exclusive.
>
> "coasting" in gear saves gas because the engine computer will cut off
> fuel delivery.  coasting in neutral will not - the computer needs to
> inject to keep the engine rotating, something provided by the drive
> train if in gear.
>
Thank you all for the advice. My car is manual transmission. I keep it
in neutral when coasting. Judging by the RPM. coasting in neutral
requires less gas than in gear. It also travel longer distance too.
From: jim beam on 13 Jun 2010 12:00
On 06/13/2010 08:12 AM, liu wrote:
> On Jun 12, 10:18�am, jim beam<m...(a)privacy.net> wrote:
>> On 06/12/2010 06:51 AM, Don Stauffer wrote:
>>
>>
>>
>>
>>
>>> liu wrote:
>>>> I'm trying some tips mentioned by these hyper-milers. One of them is
>>>> to turn off the engine while approaching the intersection with traffic
>>>> light on red. Sometimes due to the distance, I lost the power to
>>>> brake. So I tried using the 2nd gear to slow down the car. (Note: I
>>>> only do this with enough distance between cars, or I would rather
>>>> turning the engine back on.) A few times I found the power gets back
>>>> up again. Initially, I was wondering if I did turn off the engine and
>>>> then realized that this is the same as push-jump start a car.
>>
>>>> So how does it work? Why would the engine start up again without
>>>> involving the starter?
>>
>>>> Thanks,
>>
>>> If the car is in gear you are not really coasting. You need to keep on
>>> the gas a longer distance before starting your deceleration, because the
>>> car will decelerate at a higher rate when you are turning the engine
>>> over. Therefore you are not saving as much gas as when you coast with
>>> engine out of gear.
>>
>>> BTW, some of what hypermilers say works, other things do not work. Mixed
>>> bag- depends on who says it. Coasting out of gear does work, playing
>>> lights works even better (though playing and coasting are not mutually
>>> exclusive.
>>
>> "coasting" in gear saves gas because the engine computer will cut off
>> fuel delivery. �coasting in neutral will not - the computer needs to
>> inject to keep the engine rotating, something provided by the drive
>> train if in gear.
>>
> Thank you all for the advice. My car is manual transmission. I keep it
> in neutral when coasting. Judging by the RPM. coasting in neutral
> requires less gas than in gear. It also travel longer distance too.

it travels a longer distance, but only coasting in gear shuts fuel
delivery off - the engine computer is programmed that way. it /has/ to
keep on injecting fuel while in neutral or the engine will stall. rpm
is not an indicator of fuel consumption.

--
nomina rutrum rutrum
From: liu on 13 Jun 2010 18:12
> it travels a longer distance, but only coasting in gear shuts fuel
> delivery off - the engine computer is programmed that way.  it /has/ to
> keep on injecting fuel while in neutral or the engine will stall.  rpm
> is not an indicator of fuel consumption.

Does this apply only to newer cars? Mine is 1994. If you have any URL
info on this, please provide. I'd like to learn more.
THANKS!
From: Hachiroku ハチロク on 13 Jun 2010 21:40
On Sun, 13 Jun 2010 08:09:12 -0700, liu wrote:

>
>> Because you're spinning the engine with the clutch instead of the
>> starter motor.
>>
>> All the starter does is spin the crankshaft via the flywheel to build
>> compression in the cylinders and getting the fuel to ignite. You're
>> using the transmission instead of the starter motor.
>>
> Thanks for the response. That's the answer I'm looking for.

Glad to oblige! ;)


From: Don Stauffer on 14 Jun 2010 09:15
liu wrote:
>> it travels a longer distance, but only coasting in gear shuts fuel
>> delivery off - the engine computer is programmed that way. it /has/ to
>> keep on injecting fuel while in neutral or the engine will stall. rpm
>> is not an indicator of fuel consumption.
>
> Does this apply only to newer cars? Mine is 1994. If you have any URL
> info on this, please provide. I'd like to learn more.
> THANKS!

Coasting a longer distance still saves fuel even if idle fuel is not cut
off. If you travel a shorter distance, that means there is an additional
distance before coasting that you are traveling with cruise throttle and
fuel flow that you would NOT be traveling with the longer coasting distance.
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