coasting to neutral

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david

A friend of mine is claiming that fuel economy can be improved if car is
frequently being put to neutral while driving. His non turbo 850 with
automatic transmission uses 7.8 l/100km (30MPG) on a highway.



My question is if this is really a known fact and can be scientifically
proven for or against it. Is this ok practice for the transmission or other
parts.



I'd like to know what impact this has on the 850 with automatic
transmission, if any, and if this driving habit really saves gas.



I would leave discussion about safe driving, legal issues for another topic.

Thanks for your suggestions.
 
safety issues aside, I understand some automatic transmissions need to be in
gear for the internal pumps to be working properly. By putting them in
neutral, there may be a decreased fluid flow, possibly leading to damage
later on. I have no proof of this, just what I've heard over the years.....
 
I used to get amazing gas mileage out of my manual that way, but an
automatic I'd be worried about when you re-engage drive.

I know when I was looking at BMW 5's a while ago they had a good trans.
reputation unless you revved it in neutral and coasted in neutral. Basically
just leave the transmission in neutral unless stopped, at least for that
car.
 
I'm not sure where you live, but coasting in neutral is just plain illegal
in many areas. (It is here in Arizona.) If it is illegal, there is no point
in pursuing it.

However... no, it doesn't improve economy noticeably. The fuel consumption
is similarly low if you use the throttle to do the same, and overall fuel
consumption is determined primarily by the periods of acceleration and
cruising, rather than by the small amounts used during the time you could be
coasting.

Mike
 
Most of the time it's technically illegal but only REALLY enforced for big
rigs, where they're supposed to be under control at time time.

I guess if it could be proved at an accident investigation you'd be screwed
though.
 
david said:
A friend of mine is claiming that fuel economy can be improved if car is
frequently being put to neutral while driving. His non turbo 850 with
automatic transmission uses 7.8 l/100km (30MPG) on a highway.

My question is if this is really a known fact and can be scientifically
proven for or against it. Is this ok practice for the transmission or other
parts.
Click to expand...

1) It is not true. I have evidence to the contrary. My wife drives
normally leaving the car in automatic always. I always down shift the
automatic transmission when slowing down. This would be much worse than
leaving in automatic if what your friend says is true. However we get
the same gas mileage exactly so what your friend says is absolutely
false.

2) It is also harmful to the car. Read the manual. It says to never tow
an automatic transmission car at highway speeds. That is the same as
coasting with the transmission in neutral. It can damage the
transmission.

3) It is illegal in most every state, maybe all.

--
Pardon my spam deterrent; send email to [email protected]
Cheers, Steve Henning in Reading, PA, USA
Owned '67,'68,'71,'74,'79,'81,'87,'93,'95 & '01 Volvos.
The '67,'74,'79,'87,'95 and '01 through European Delivery.
http://home.earthlink.net/~rhodyman/volvo.html
 
david said:
A friend of mine is claiming that fuel economy can be improved if car is
frequently being put to neutral while driving. His non turbo 850 with
automatic transmission uses 7.8 l/100km (30MPG) on a highway.
Click to expand...

I disagree. When you lift your foot off the gas above about 1500rpm,
the fuel is cutoff from the engine. The engine probably uses less
fuel in this case than it does idling in neutral.
 
2) It is also harmful to the car. Read the manual. It says to never tow
an automatic transmission car at highway speeds. That is the same as
coasting with the transmission in neutral. It can damage the
transmission.
Click to expand...

That's the same though, in the case of the question, the engine is still
running so the hydraulic pump is still turning pumping fluid in *most*
automatic transmissions. Still I wouldn't advise shifting to neutral,
there's no gain, in fact it'll probably use more fuel to keep the engine at
idle speed than to let the innertia of the car spin it, won't happen nearly
to the same extent as with a manual but even with an automatic there's still
some engine braking.
 
A friend of mine is claiming that fuel economy can be improved if car is
frequently being put to neutral while driving. His non turbo 850 with
automatic transmission uses 7.8 l/100km (30MPG) on a highway. [..]
I'd like to know what impact this has on the 850 with automatic
transmission, if any, and if this driving habit really saves gas.
Click to expand...


Well now; the old Rovers of the 50s and early 60s had a freewheel
device fitted to them for just this purpose. It also made clutchless
gearchanges a doddle. Whether they made any real saving is debatable,
but as the UK was just emerging from an era of wartime fuel rationing
it seemed to make sense. Freewheeling in neutral was common practice
then.

As to whether you will actually save on your fuel bills, well it
probably all depends upon your normal driving habits. Freewheeling on
the flat will mean you are constantly slowing down. This may save you
some braking, and as brakes converts fuel-induced kinetic energy into
heat that is lost to the atmosphere, then there may be a saving. But
if you slowed down a little earlier anyway, so that you similarly had
to do less braking, then you will make a similar fuel saving.

If you coast down a hill that you would otherwise have a closed
throttle on, then there will be very little, if any, fuel saving (a
closed throttle can mean cutting the fuel at speeds above idle),
though arguably there may be a little to gain if you can roll on at
the bottom where you would otherwise need to open the throttle.

A disproportionate amount of fuel is used during accelleration, which
is why constant speed cruising is significantly more economical that
stop-start use. But the other side of the coin is braking. Everytime
you brake, this represents lost energy that originated in the fuel.

I reckon that freewheeling can make apparent gains because it forces
you into a more economical driving style. Adopt this driving style
anyway and you will make the same savings without resorting to
neutral. Plan ahead, be smooth, do everything with restraint.
--

Stewart Hargrave


For email, replace 'SpamOnlyToHere' with my name
 
Jim Carriere said:
I disagree. When you lift your foot off the gas above about 1500rpm,
the fuel is cutoff from the engine. The engine probably uses less
fuel in this case than it does idling in neutral.
Click to expand...
The difference is that with the transmission in neutral there would be
no engine braking, so the car would be free to go downhill faster
while still using only a tiny amount of fuel.
 
It's very effective, BUT... and this is huge - if you miss
a shift or guess the gears wrong, you can literally blow out
your snycros in seconds. With an automatic, it won't
engage if it's too high, but going from 500 rpm to 4500rpm
when it does engage is very very hard on the car - and there
will be a huge amount of engine-braking that hits hard enough
to be a potential handling problem.

Neither one is a good outcome if you mess up. Gas is cheaper
than a clutch, afterall.
 
Your biggest fuel saver in the item attached to the gas pedal when
you're driving -- your foot.

I recall a study where they told two drivers of identical cars to go
from A to B along the Autobahn and German roads. Difference in
instruction was that one was told "minimum time", the other told
"stick to the speed limit, drive in a moderate manner, and enjoy the
drive".

Difference in transit times was almost the same; difference in gas
consumption, big difference.

I'm stuck in a commute situation every day. On lucky days, I get a
clear road; on really bad days, I'm idling. This is with a regular
5-cylinder 1994 850 with automatic.

Once the car starts hitting 110-120 KPH (65MPH for those non-metrics),
my consumption goes up by about 25% over the regular consumption.
(using the estimated range feature before and after trips.)

Use of a manual transmission combined with good driving habits and
keeping the speed down (no hard or prolonged high-speed runs), you're
laughing.

My wife proved that when we both drove Ford Escorts (2.0 hers was
manual, mine was automatic.)
 
This is the perennial story told about ZF automatic gearboxes. The pump is
only disconnected when in Park. Hence the rule about not revving the engine
(as at emissions checks in UK) when Park is selected. Neutral is perfectly
OK as is D on a rolling road or with the rear wheels lifted clear of the
ground. The other Volvo model using a similar gearbox is the 400 series auto
(non-CVT) which is FWD so would need the Front wheels lifted clear of the
ground if D is used.

Cheers, Peter.
 
The old truckies used to call neutral gear while on the move "ANGEL gear"
guess why ?
 
Because they used manual gearboxes. It was also a way to defeat the governor
and obtain much higher speeds out of the trucks.

Cheers, Peter.
 
Hi Peter,

I should have thought that truckers called neutral gear while on the move
"Angel Gear" because it was a sure "gateway" to Heaven to meet the
Angels..............

Andy I.

| Because they used manual gearboxes. It was also a way to defeat the
governor
| and obtain much higher speeds out of the trucks.
|
| Cheers, Peter.
|
| | > The old truckies used to call neutral gear while on the move "ANGEL
gear"
| > guess why ?
| > | >>
| >>> A friend of mine is claiming that fuel economy can be improved if car
is
| >>> frequently being put to neutral while driving. His non turbo 850 with
| >>> automatic transmission uses 7.8 l/100km (30MPG) on a highway.
| >>>
| >>> My question is if this is really a known fact and can be
scientifically
| >>> proven for or against it. Is this ok practice for the transmission or
| >>> other
| >>> parts.
| >>
| >> 1) It is not true. I have evidence to the contrary. My wife drives
| >> normally leaving the car in automatic always. I always down shift the
| >> automatic transmission when slowing down. This would be much worse
than
| >> leaving in automatic if what your friend says is true. However we get
| >> the same gas mileage exactly so what your friend says is absolutely
| >> false.
| >>
| >> 2) It is also harmful to the car. Read the manual. It says to never
tow
| >> an automatic transmission car at highway speeds. That is the same as
| >> coasting with the transmission in neutral. It can damage the
| >> transmission.
| >>
| >> 3) It is illegal in most every state, maybe all.
| >>
| >> --
| >> Pardon my spam deterrent; send email to [email protected]
| >> Cheers, Steve Henning in Reading, PA, USA
| >> Owned '67,'68,'71,'74,'79,'81,'87,'93,'95 & '01 Volvos.
| >> The '67,'74,'79,'87,'95 and '01 through European Delivery.
| >> http://home.earthlink.net/~rhodyman/volvo.html
| >
| >
|
|
 
'Coasting' in gear will increase the fuel economy, because manufacturers
program the engine ECU to deliver no fuel to the combustion chambers in this
event. This applies to manuals & autos. Coasting in neutral can be
dangerous, as the inertia of the engine when coasting in gear allows safe
control of the vehicle. In UK driving lessons we are taught this, though I
think it is not actually illegal to do it. This may be because it is hard
to prove without specialist diagnostic equipment. I also suspect trying
coasting in neutral with an auto could well be dangerous.
 
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