Best MPG : 5-speed vs. auto?

"Don Stauffer" > wrote

> Also, when you see a light ahead, shift into
> neutral and coast. Yeah, it is illegal in many states, but those laws
> were written when brakes were primitive and gas was a quarter a gallon.

Do you know how much fuel is wasted trying to idle? Injector pulse
width goes up upon idling. With that amount of fuel you can go twice
or more of the distance you coasted in neutral to a stop. This can
also wear your brakes and your auto transmission prematurely. You'll do
better gas-wise with the motor shut off but that only save less than 1/4 of
a cup with all the effort.

Who ever made it illegal to drive in neutral also made ridiculous law
such as to shift into lowest gear (not neutral) if the engine accelerates
out of control (even on a level road.)

Ted Mittelstaedt wrote:
> "Don Stauffer" > wrote in message
> ...
>
>>* wrote:
>>
>>>Computer-controlled transmissions can now shift gears at exactly the
>>>correct moment......
>>>
>>>If it is fuel mileage I'm looking for, I'll take an automatic over a
>
> stick.
>
>>>
>>>
>>No way! We traded in a Voyager stick for a new Chrysler van. The auto
>>in the new one shifts at WAY higher rpm than we did with the old one,
>>and we get nowhere the milage. You can short shift a stick- newer ones
>>with computer control, you can't even FORCE an upshift! And the
>>computer wants to supply AVERAGE driving program. If I knew how to redo
>>programming I would.
>>
>>Anyone know if the dealer shop can alter the shift point?
>
>
> Most Chrysler minivan sticks were on the short wheelbase 2.5L you have
> a 3.8L in a long wheelbase there now that weighs a hell of a lot more.
> If you had a stick on there you would get even worse mileage.
>
> Ted
>
>


Nope- the van IS a short wheelbase. Chrysler does make them. However,
it has the second sliding door which does increase weight some. But the
high shift rpm has GOT to be responsible for some of the milage loss.

Ted Mittelstaedt wrote:
> "Mike Romain" > wrote in message
> ...
>
>>Don Stauffer wrote:
>>
>> Also, when you see a light ahead, shift into
>>
>>>neutral and coast. Yeah, it is illegal in many states, but those laws
>>>were written when brakes were primitive and gas was a quarter a gallon.
>>>
>>
>>I just don't get idiots that come onto a world wide web boasting about
>>doing highly illegal and deadly practices while saying 'forget what they
>>used to say', it's cool now to go out of control and potentially kill
>>yourself or others....
>>
>
>
> I didn't realize that when you shifted into neutral that your brakes
> stopped working.
>
> I'll cite another ancedotal study I can't find right now, they did a
> study of accidents, out of the 200+ or so they found only 5 where
> the driver would have been better off accellerating in an attempt
> to avoid a collision. All others it made no difference or the driver
> would have been a lot better off braking harder.
>
> The idea that you lose control in neutral is baloney. You still have
> steering and brakes, and in most collisions I've seen there was plenty
> of room for the drivers to swerve to avoid. They call it taking
> evasive action. The problem is that most drivers in the few seconds
> before a collision happens, freeze up and do not steer away from
> the impending collision, and as a result many collisions happen that
> wouldn't have happened at all had the driver swerved.
>
> Particularly in city driving when the car is seldom above 35Mph, the
> idea that your going to be able to downshift during a deaccelleration from
> 35Mph to 0Mph, and be able to suddenly power out of the way of
> an impending collision, is poppycock. The engine is not going to be
> in the right gear to be able to punch it and power out of a collision.
>
> Ted
>
>

By coasting in neutral or with clutch in means you coast further, so you
can back off gas earlier. Using the brakes would mean staying on gas
longer, using some fuel.

I keep aware of what other drivers are doing, so I can shift back into
gear mucho fast if I need to. However, with brakes on cars these days I
believe instances where acceleration is key are rare. Rather, the
lateral avoidance CAN be a key. I know how to modulate braking so as to
not lock brakes, and still retain steering.

I think most of these laws were put on the books before 4-wheel and
hydraulic brakes.

dnoyeB wrote:

>
> I don't like that. 'lugging' the engine is what happens when you shift
> too soon. YOu need to shift soon enough to balance the acceleration you
> get after the shift with overdriving in the gear you are shifting from.
> Don't shift ASAP. That just waste gas.
>
>
>

How does that waste gas? You have to have a wider throttle opening to
accelerate, which SAVES gas as long as the opening is so wide that power
mixture enrichment comes into play.

With small throttle openings efficiency is poor, because it is the
ACTUAL compression ratio that determines efficiency, NOT the geometric
one. One needs a high pressure in cylinder during combustion to get
high thermal efficiency.

Ted Mittelstaedt wrote:
>
> "Mike Romain" > wrote in message
> ...
> > Don Stauffer wrote:
> > >
> > Also, when you see a light ahead, shift into
> > > neutral and coast. Yeah, it is illegal in many states, but those laws
> > > were written when brakes were primitive and gas was a quarter a gallon.
> > >
> >
> > I just don't get idiots that come onto a world wide web boasting about
> > doing highly illegal and deadly practices while saying 'forget what they
> > used to say', it's cool now to go out of control and potentially kill
> > yourself or others....
> >
>
> I didn't realize that when you shifted into neutral that your brakes
> stopped working.
>
> I'll cite another ancedotal study I can't find right now, they did a
> study of accidents, out of the 200+ or so they found only 5 where
> the driver would have been better off accellerating in an attempt
> to avoid a collision. All others it made no difference or the driver
> would have been a lot better off braking harder.
>
> The idea that you lose control in neutral is baloney.

No it isn't.

When you are coasting in neutral, the suspension is unloaded. This
means all the parts are loose and floppy. If you have any worn parts,
this looseness can translate into loss of control 'very' quickly.

Read your owners manual and see what it states.

Coming onto a world wide forum and telling folks it's ok to coast in
neutral is liable to get someone killed.

I off road a lot and see accidents that happen because the person was
coasting in neutral. It is bad news to do, especially in snow or
slippery conditions.

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's
Canadian Off Road Trips Photos: Non members can still view!
Jan/06 http://www.imagestation.com/album/pi...?id=2115147590
(More Off Road album links at bottom of the view page)

"When you are coasting in neutral, the suspension is unloaded. This
means all the parts are loose and floppy. If you have any worn parts,
this looseness can translate into loss of control 'very' quickly. "

You indicate that for slipperey conditions and off-roading, this is
especially true (particularly so for large tires, I'm sure). Won't
argue (much) with that.

For street driving, based on my experience with cars in good and bad
repair, front-wheel drive, rear-wheel drive, and 4WD, I gotta call
bull****. Maybe has some creedence when going down a steep hill. Maybe.

Dave

wrote:
>
> "When you are coasting in neutral, the suspension is unloaded. This
> means all the parts are loose and floppy. If you have any worn parts,
> this looseness can translate into loss of control 'very' quickly. "
>
> You indicate that for slipperey conditions and off-roading, this is
> especially true (particularly so for large tires, I'm sure). Won't
> argue (much) with that.
>
> For street driving, based on my experience with cars in good and bad
> repair, front-wheel drive, rear-wheel drive, and 4WD, I gotta call
> bull****. Maybe has some creedence when going down a steep hill. Maybe.
>
> Dave

Physics are the same on road as off road.

Just read your owners manual. If it is safe it will state so. I'll bet
it will say something like mine does: WARNING: Do not coast in neutral.
You might lose control of the vehicle.

One problem with doing it is if you get in the habit and mistakenly
think you are saving gas, (most FI engines have a decelerate mode that
is way lower than idle for fuel use. That is why they stall with no
speedo working) you will end up coasting down that one damn hill with
the one off camber curve and that pot hole that you couldn't see in the
dark or flat light and.....

Besides coasting down hill is illegal in most places. Cops can tell
because the vehicle floats loose. I have had a cop tell me this at the
bottom of a short hill I got caught coasting down. Got a lecture
instead of a ticket at least.

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's
Canadian Off Road Trips Photos: Non members can still view!
Jan/06 http://www.imagestation.com/album/pi...?id=2115147590
(More Off Road album links at bottom of the view page)

Mike Romain wrote:

> ...
> Besides coasting down hill is illegal in most places.
> ...

Coasting down hills is a different story than popping it into neutral 20 or
30 yards before coming to a stop at a light, which is what I, and I think
several others, thought we were talking about.

ZZ wrote:
>
> Mike Romain wrote:
>
> > ...
> > Besides coasting down hill is illegal in most places.
> > ...
>
> Coasting down hills is a different story than popping it into neutral 20 or
> 30 yards before coming to a stop at a light, which is what I, and I think
> several others, thought we were talking about.

Ok, agreed. I will repeat myself for the part you missed....

In that case, besides if the road is on a slope so it can be called a
downhill, most FI vehicles have a deceleration mode that sends less fuel
to the engine than a neutral idle mode does.

In the case of Jeep for sure, if the speedometer pickup isn't sending a
signal to the computer, it will 'assume' deceleration mode and the
engine will stall if you 'coast' in neutral.

To me this means it is more efficient to decelerate 'in gear' as the
owners manual clearly states, not in neutral which is dangerous and
actually wastes gas...

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's
Canadian Off Road Trips Photos: Non members can still view!
Jan/06 http://www.imagestation.com/album/pi...?id=2115147590
(More Off Road album links at bottom of the view page)

Mike Romain wrote:

>
> In that case, besides if the road is on a slope so it can be called a
> downhill, most FI vehicles have a deceleration mode that sends less fuel
> to the engine than a neutral idle mode does.
>
But the fuel savings I am talking about is the fuel savings in running a
shorter period of time before you back off and coast. Even with NO fuel
going into engine, because of irreversible thermal losses, an "air
compressor" takes energy to turn over. A car in gear and coasting
coasts a shorter distance, or will arrive at a given point ahead of the
initiation of the coasting point at a higher speed, if the car is taken
out of gear instead of coasting in gear.

If it arrives at a higher speed when the light changes, it will not need
to accelerate from a lower speed. The higher the speed you coast
through a light, the less fuel it takes to regain cruise speed. And, the
sooner you back off and coast, with a longer coasting distance, the less
fuel you needed to coast to any point.