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I have had it suggested to me that to increase MPG I should select 'N' and let the vehicle 'coast' wherever possible - eg approaching traffic lights, motorway off slips etc. Views?1. Since the engine continues to turn in 'N' anyway will I actually save enough to make it worth it - to get the 'ecostop/start' to work you presumably would have to select 'D' again when stationary at the lights?
2. Are there any dangers in drivng an automatic with the engine disengaged in 'N'?
3. Any other risks or benefits anyone can see?
 

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Nope that's not the case.

In neutral the car need to always supply fuel to keep the engine turning.
In gear it can work out it's "coasting" and so cut fuel completely.


Well that's how most engine management systems work these days.



I don't think it's good practice to drive an auto car in neutral anyway.






Edited by: Nev
 

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I'm not sure about the auto box but manual cars will use more fuel if slipped into neutral and coasted rather than just coasting.it may seem strange but when the engine is idling, the injectors are squirting fuel into the combustion chambers to enable the engine to maintain minimum revs however when coasting in gear there is no need for fuel as the cars momentum is turning the engine which is slowing the car down due to friction. The difference may be minor but it exists.

The other thing about coasting in neutral is you do not have full control of the vehicle.
 

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Out of interest, was the person who suggested this to (dare I say it...) old?

Putting an automatic gearbox in to N is a very old school way of thinking. Modern auto transmissions do not benefit much by slipping the car in to N, especially not when stationary. In fact, I'm sure that when you do select N when stationary, the engine revs a little higher than in D, perhaps another 200RPM or so.

The coasting functionality of some very new cars (Porsche Macan springs to mind) decouples the engine to prevent any engine braking. This is only helpful if you intend to keep moving - if approaching a set of lights, it's almost a waste as you'll have to use your brakes more, as your engine isn't doing some of the braking for you.

Technically speaking, coasting is a fuel efficiency function. "The coasting function enables you to save even more fuel where the situation allows. The engine is decoupled from the transmission, which avoids the deceleration caused by engine braking. In this way, the vehicle makes optimum use of its own momentum and is able to coast for longer distances. This has real benefits for fuel consumption without any impact on comfort or sporty performance." source

Regarding your questions above:
1 - Unlikely that switching to N at lights will save fuel.
2 - Yes; if you need to accelerate suddenly, you'll have a 2 second delay (between your reaction and the engine re-engaging) which may adversely affect you in an emergency situation. Also, this type of behaviour requires cognition, so you're focusing on another task/process whilst driving.
3 - I think the risks far outweigh any potential benefit you'll experience. I'd advise anyone against this type of behaviour.Edited by: Evoque Down Under
 

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My Caddy van is a DSG auto, if you let off the gas it's like dipping the clutch, the revs drop and it coasts, very unnerving on the motorway where I like to engine brake. To get over this I have to just tap the brake peddle then the clutch re engages so the van will engine brake. I think the Evoque is much better to drive because Ii like to use engine braking and I was taught this way also..
 

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Evoque Down Under said:
The coasting functionality of some very new cars (Porsche Macan springs to mind) decouples the engine to prevent any engine braking. This is only helpful if you intend to keep moving - if approaching a set of lights, it's almost a waste as you'll have to use your brakes more, as your engine isn't doing some of the braking for you.

Regarding your questions above:
1 - Unlikely that switching to N at lights will save fuel.
2 - Yes; if you need to accelerate suddenly, you'll have a 2 second delay (between your reaction and the engine re-engaging) which may adversely affect you in an emergency situation. Also, this type of behaviour requires cognition, so you're focusing on another task/process whilst driving.
3 - I think the risks far outweigh any potential benefit you'll experience. I'd advise anyone against this type of behaviour.
The new Porsches do indeed have the automatic decoupling feature enabling the coast function, but when going downhill and using the brakes, the gearbox will select the correct gear, even changing down further if it necessitates it.

Regarding the switching to neutral on the Evoque, I totally agree with EDU on his above suggestion.
 

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I never coast in N , but I do select N ant lights as I don't like the car trying to move and it can't be good held on the brakes

Also you have to press brake pedal to re select D when moving
 

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I put mine in P at lights, I don't like leaving my foot on the brakes, especially after "spirited" driving
 

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P ?
When driving auto I'd select N and put on the EPB. Saves going past R and scaring the peeps behind!
 

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CoolBlueWhyte said:
P ?
When driving auto I'd select N and put on the EPB. Saves going past R and scaring the peeps behind!
Ah, I never thought of that, not had an auto before
 

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CoolBlueWhyte said:
P ?
When driving auto I'd select N and put on the EPB. Saves going past R and scaring the peeps behind!
I do this, but the parking sensors become active, then if somebody comes too close behind, off they go.
 

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I think we've gone off topic again discussing neutral when parked not moving!

If the best MPG is your ultimate goal then coasting in neutral is one of the tools that can be used (if used in the correct manner i.e. coasting down hill, not slowing for a junction). As EDU points out the Macan does this itself by decoupling the drive.

On its own it will not save much, you have to combine it with other things, like removing all the unwanted crap from your boot (including the spare if MPG is really your goal), tyre pressures are correct, engine serviced with clean oil and filters, etc.
The biggest effect is based on your driving style, speed and planning. Adjusting road speed so that you do not have to stop at junctions and roundabouts. Try to avoid driving in rush hour by planning you journey times.
All this added together will make a big difference to your mpg, just one of these will hardly be noticed.
 

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Going on a diet and driving around just wearing budgie smugglers might help too
 

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Sorcerer said:
The new Porsches do indeed have the automatic decoupling feature enabling the coast function, but when going downhill and using the brakes, the gearbox will select the correct gear, even changing down further if it necessitates it.
Good to know Sorc, thanks for the info


Gary pa28 said:
Also you have to press brake pedal to re select D when moving
That's not true Gary - near my home, I often coast down a big hill and slip in to N (at about 60km/h). When the hill flattens out, I slip it back in to D without pressing the brake pedal whatsoever.
 

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If MPG is a concern, you can use the ECO/Advance trip to monitor your driving style and adjust accordingly.

As has been said, coasting in neutral down hills will increase your fuel consumption.
 

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RM - are you going to post some pictures of your driving atire :)

Nev - Sadly only MY14 onwards are blessed with the Eco readouts.

I think this post agrees that you CAN save fuel by coasting in neutral, if it is safe to do so and you do not want the engine braking to scrub off speed and slow you down.
When you consider that most people leave their engine idling when stationary is a real bonus if it's idling and you are doing sixty!

EDU - just think of all that effort you will save on the big hill in your new Macan flicking from D to N to D.
 
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