Coasting

Hello,
I have been reading up on hypermiling, a technique that employs some
very common sense ways to increase mileage. But it also involves
turning off the engine and coasting, something I do not think is wise,
due to the loss of power steering and power brakes. I have a 2003
Accent, manual transmission. Does it do any harm to put the car in
neutral and coast with the engine still running at idle?
Thanks

 

It seems like I read in Car and Driver magazine, in one of the editorials
or car articles a few months back, that they just mentioned in passing that
they found no difference in mileage doing this. The article was about
something else but related. Just fyi.

Maybe because if you're foot's off the gas, no matter what the rpm says,
the same amount of gas is being injected for 'idle' speed. The cylinders
are just moving faster in gear because the wheels are turning faster, the
engine isn't compensating by giving(wasting) more gas to keep up. But it
sounds like it because engine rpm is still engine rpm, with all the
associated sounds, whirrs, hums, roars, etc. regardless of how much gas is
incoming. Seems logical.

 

There'd be no threat of damage to the car. Most jurisdictions, however
make it illegal to have the transmission in neutral or the clutc
disengaged when crossing railroad at least in certain circumstances.

At the very least, no noticeable difference in fuel economy is a plausibl
finding. When coasting with the car in gear, as long as the engine i
turning at idle rpm, you have engine braking, but the ECM cuts all fuel t
the engine (since it isn't needed). On the other hand, with the car i
neutral, you don't have the engine braking, but you're using the necessar
gas to keep the engine running

 

i was going to say what hyundaitech said. I'll add this. There is a
lot of "old wisdom" floating around that came from the days of
carburated engines that often used more gas at idle than driving
slowly. If you are coasting down a hill then you need the engin
braking unless you can safely let the car accelerate down the hill for
a long period of time. Short bursts won't buy you enough gas saving
to matter and can be offset by brake wear. If you are city driving
you will find anticipating lights and developing a smooth driving
practice is most productive. For highway driving cruise control is
your friend.

My $.02, worth every penny you paid for it. ;-)

 

I agree with what has been said in this thread thus far, but I have a
puzzling question: Why do I get better gas mileage using neutral on my
2006 Sonata V6 ATX?

Here's my case and maybe something is wrong with my car, but I doubt it.

Same exact stretch of road near my work has a very long (about a mile) with
a mild grade. I'd guess about 3-4% or so. Nothing major.

I approach the top of the incline (start of descent) at exactly 45 MPH.
Keeping the car in "D", with my foot completely off the gas, I am doing 46
MPH at the bottom of the hill. Putting the car in neutral has me going 56
MPH at the end of the incline.

Why? Should there really be that much engine breaking, or is this
transmission drag?

Eric

 

Probably normal torque converter drag.

There's another kind of "coasting" that definitely saves fuel. Simply
getting off the gas a little earlier when making stops can save fuel
and brake pads. I see a lot of people doing 75mph get on their brakes
without first coasting down to a reasonable speed. I don't have any
figures, but that must be very wasteful.
-

Bob

 

Sure, it all depends on drivetrain design. My Buick has little drag, but my
former Mercedes diesel would probably be doing 30 at the end of that hill.
As for coasting, you can get better mileage as long as you can use the
gained speed and not just waste it by putting on the brakes.

 

Yeah, Bob, that's what I figured too. I just think this car could get so
much better mileage overall with much less of that drag.

And your 100% right about the braking. Actually, it all goes to the
overall smoothness of the ride. The less g's your pull, either positive or
negative, from accelerating or braking, will improve your mileage. The
lateral g's in a turn don't effect mileage as much, but if you are
scrubbing off speed it will.

Eric

 

That's the truth. Unfortunately, at the end of this hill is a light. It's
green for me about 70% of the time. When that's the case, I can usually
get about 4 miles of coasting while still maintaing the speed limit.

Anyway, even longer story short, but by practicing my "smoothness", and
coasting where it is beneficial and SAFE, over the last 6 months I have
managed to increase my mileage by an average of just over 2 MPG. I am now
at 24.6 MPG (6 month average) versus 22.5 MPG. And my driving is 80% city
with a V6 Sonata.

Eric

 

For highway driving cruise control is

Unless there are hills to climb. CC will try and maintain the selected
speed whereas if you hold a steady pedal pressure up hill and let the
speed drop, you'll save a few drop of the precious fluid.

I practice hypermileage techniques with both of our stick shift cars
and I'm seeing about a 10% mileage improvement.
I think most of the savings come from accelerating like there is a egg
between my foot and the gas pedal followed by coasting and higher tire
pressure.
L.

 

This is true with respect to stopping, but not with respect to
acceleration. The is an optimal acceleration curve that will maximize
fuel economy. Most cars get optimum economy in the 40-50 MPH range.
Driving too long at speeds less than that will cause a lose in overall
economy. So, you generaly want to accelerate smoothly to at least 40
MPH. You don't want to floor it to be sure, but taking two miles to
accelerate to 55 MPH will take more fuel than a more reasonable
acceleration that gets the car into the "sweet zone" sooner and keeps it
there longer.

Matt

 

Matt Whiting wrote:

Interesting! I'd like to know *why*. Is it from being in a higher
gear?

And a related question I've wondered about for some time:
I often get stuck behind people who accelerate so *slowly* I want
to scream. I'm guessing these people are subscribing to the
"drive like you have an egg between your foot and the gas pedal"
school of driving.

I'm sure this was reasonable advice back in the day when
stomping the accelerator pumped large amounts of gas down the
carb throat, but how much difference does it make with FI cars?

Sure, it's going to take a little more gas to accelerate at a
reasonable rate than just gathering inertia, but enough to make
an appreciable difference in MPG?

My peeve is that such drivers, IMHO, contribute to traffic
congestion by leaving the "backed up" cars behind them to sit a
traffic lights they would have "made" otherwise, etc. Which
doesn't do anything for *their* gas milage.

Please note I'm not talking about peeling rubber or "jackrabbit"
starts, just no-nonsense, "get 'er done" starts.

 

Yes.

 

Too bad. You can swear and pound on the steering wheel all you want
but you don't own the road.

Most tests say 4-5%, some quite a bit higher. Combine that with other
gas saving measure and it could amount to over 30% according to the
Edmund's test.

Your comment is complete speculation unless you know how the lights
are timed. Someone somewhere down the line is not going to make the
light no matter what the conditions.Sorry you're annoyed with people
that don't drive like 'you' think they should drive. Take a deep
breath and try and calm down, your attitude could lead to road rage
with all its dire consequences.

L.

 

Curlyque wrote:
your attitude could lead to road rage

No question about the road rage. My Brother in law, a state trooper,
said that out of all the incidents of road rage he's dealt with, the
driver that got the ticket said the same things.
The person in front was blocking traffic, and, or driving too slow in
the left lane. The slow drivers comment: He doesn't own the road.

The unfortunate thing is, slow drivers don't get it either, they think
everyone should follow their lead, but they are the ones causing the
irritation.

If you want to drive slow be courteous and allow others to get by, and
don't drive in the left lane. If you want to drive fast, be patient, NOT
aggressive, and pass on the LEFT.

Clay

 

Those aren't my feelings, but I do feel that the less aggresive driver
should have the right of way, not the other way around, especially
since the topic is saving resources. It's just the way it plays out.
No matter how slow one goes, there is always someone slower. No matter
how fast one goes there is always someone who wants to drive faster.
Each driving situation calls for a separate evaluation and action.

JMHO

L.

 

What it boils down to is that you consider someone driving faster than
you "aggressive".

I say I won't ride your ass, ever, if your in the right hand lane. If
you are in the left lane I expect you to move over at your first
opportunity, when you see a faster driver behind you. It's called
driving etiquette.

This is the way drivers around the world behave. Everyone is welcome to
save fuel all they want, just don't force me to do it.

Clay

 

How does being the faster of two drivers equate to being more aggresive?
Being more urgent in life has nothing to do with aggression.

Of course, but as was stated, as often as genuinely aggressive drivers pose
problems, so do those who sputter along with the attitude that this is fast
enough, and everyone else around me should be satisfied at this pace. There
is a reason that most states have laws about obstructing the flow of
traffic. To quote a phrase, "especially since the topic is saving
resources".

 

When someone exceeds the speed limit they are agressive and breaking
the law. I won't yield an inch to that kind of driver.

The minimum speed limit on an interstate, and most other roads with a
speed limit of 55 and over, is 45. Consider it your lucky day if I
decide to go the speed limit not the minimum. I am within the law and
I'll decide how fast I want to go. Not everyone is urgently moving
from one place to another. What are you going to do when gas is 15 a
gallon and the roads are full of bicycles and scooters, lay on the
horn, cuss them out, run them over?

 

No one is saying that you can't go 45. Since the minimum speed limit is
45, as you say, and since I am sure that you are aware that the left
lane is for passing only, we should not expect that you will be slowing
down the normal flow of traffic in the left lane. Perhaps you are also
aware that bicycles and scooters, under a minimum size, are barred from
the interstates as well so you raise a moot point about what people may
do when encountering them on the interstate.
By the way I admire your attitude that one should consider it their
lucky day that you decide to go the speed limit. Just as the fast
driver may be a hazard to the general motoring public so might the slow
one, as the real problem in interstate driving is not the speed that the
motorists are going but the differential in speeds among those motorist.
That is why, if you were to watch auto racing, you would see few
wrecks (other than those caused by equipment failure) that are not the
result of a slower driver being hit from behind.