It's normally my brain that's coasting in neutral but since owning a 170 DSG I have adapted my driving style so that I flip the lever into neutral on some downhill stretches and flip it back into Drive for engine braking when on the same downhill or when I need to go again.

The DSG box appears to handle this action very well, in fact it dis-engages/re-engages the clutch(es) about as well as I could do it with a manual box and appears to be causing no harm to the driveline.

I was wondering if anyone else has adopted this driving style and if there is anyone that knows why the DSG box shouldn't be used in this way?

I accidentally nudged the lever into N and was cautious about putting it back in D with the car still moving, but it was fine, so I can't see any problems. I'm sure someone will say you shouldn't though

No, you shouldn't - not for technical reasons, but because the engine braking is a help especially in slippy conditions. Also, as the Police Advanced Driving would tell you (in their R'oadcraft' book), you should always be in a 'gear' so that you can respond to any road situation which develops without fumbling for the gear lever.

if you coast down hill in neutral, whilst the gearbox will be fine you are not in proper control of the vehicle plus you are wasting fuel for no reason. If you leave the car in D whilst running down hill the car will use zero fuel as long as your foot remains off the throttle, the forward momentum and gearing are sufficient to keep the engine turning with no fuel being used.

I have noticed in our Fabia DSG that when travelling down hill, the gearbox actually drops one or two gears, this in effect improves engine braking.

I have to go with the majority here and say, leave it in D as it will use no fuel on the overrun and keep you in control of your car.

Using N will use more fuel than keeping it in D with foot off.

OK, so technically not a problem, that was the answer I was looking for. On the safety side, fair enough. As for using more fuel, I'm not sure how that works, in neutral the engine will idle, with it in drive it will effectively still be idling to keep the engine running, so there should not be a difference in consumption?

Also depending on the hill engine braking may slow you down too much requiring you to use the throttle thereby using more fuel.

in neutral the engine will idle, with it in drive it will effectively still be idling to keep the engine running, so there should not be a difference in consumption?

In D the wheels will be turning the engine at idle, so it does not need to use fuel. This is very noticeable in our Polo as the 1.9 lump is pretty loud when its burning fuel. Not a sound when downhill with foot off in gear. Until it flattens out and the RPMs drop, then you can hear it firing again.

In D the wheels will be turning the engine at idle, so it does not need to use fuel. This is very noticeable in our Polo as the 1.9 lump is pretty loud when its burning fuel. Not a sound when downhill with foot off in gear. Until it flattens out and the RPMs drop, then you can hear it firing again.

This is absolutely correct. However, while leaving the car in gear will not use any fuel (because the forward momentum of the car turns the engine) the extra rolling resistance created by the engine means you won't coast as far as you would in neutral.

I have noticed in our Fabia DSG that when travelling down hill, the gearbox actually drops one or two gears, this in effect improves engine braking.

Agreed. Mine does the same so there's actually no need to put it to N...

I was intrigued by the answer to this and the eco-driving internet community seems to be a torn between in-gear, neutral and pulse. It is a fact that in-gear uses zero fuel on all but highly tuned cars and provides infinite mpg until the rpm drop below a certain level. But the fact that you coast further in neutral is an important factor. Pulse seems to be the most plausible, but I've concluded that it depends on the driving conditions, the car and whether a bit of engine braking is desirable. So I'll be staying safe and keeping it in D.

I used to do this with my Octavia Vrs when I owned it. I would slip it into neutral when heading down a slip road or a gradient that would keep the car rolling without it slowing down. I did notice that if it was left in gear you would have to keep your foot on the accelerator a lot longer to make it up the slip road, which would obviously use more fuel. I never had any problems with the DSG or crashed out of control during the year I owned the car.

I've now got my Superb greenline and I do exactly the same. It's surprising how far the greenline can coast on a slight gradient, even in a 30 limit. I put the car back in gear when when I want to slow down to use the engine braking. Obviously the fuel saving would not cover the costs of replacing the brakes prematurely.

its probably best to manually shift the dsg to a high gear to avoid too much engine braking and take foot off throttle.

I used to do this with my Octavia Vrs when I owned it. I would slip it into neutral when heading down a slip road or a gradient that would keep the car rolling without it slowing down. I did notice that if it was left in gear you would have to keep your foot on the accelerator a lot longer to make it up the slip road, which would obviously use more fuel. I never had any problems with the DSG or crashed out of control during the year I owned the car.

I've now got my Superb greenline and I do exactly the same. It's surprising how far the greenline can coast on a slight gradient, even in a 30 limit. I put the car back in gear when when I want to slow down to use the engine braking. Obviously the fuel saving would not cover the costs of replacing the brakes prematurely.

My daily commute involves quite a few hilly country routes which is why I have adopted this driving technique. The risks of losing control using this technique are remote, anticipation, forward planning, relaxing driving and 30 years driving experience etc blah are everything, I hardly use the brakes and the Superb can coast with ease.

You can check yourself the effect of going down hill in neutral or in gear. Firstly put the display into instantaneous fuel consumption.

If you coast in Neutral with no throttle it will show something like 170-200mpg which means it is still putting a small amount of fuel in the engine. Now on the same downhill stick it in the correct gear and lift your foot completely off the throttle. The instant fuel display will now show -----

What ------ means is absolute zero fuel consumption. Because the ECU knows you are in gear and the engine crank or cam sensor can detect that the engine is running above idle speed with no throttle due to it being turned by the gearbox then it completely shuts off the fuel to the engine and only switches it on again if it detects that the engine might stall or if you add throttle.

If you coast in neutral with no throttle then the ECU realises that it has to add fuel to stop the engine from stalling on you completely as the gearbox is unable to keep the engine turning as it is not connected in neutral.

Edited 29 December, 201213 yr by Pesmog

I often coast if the road is quiet and there is no danger in doing so. I know you use slightly more fuel than staying in gear but, as has already been mentioned, you can go much further without having to use the power. I do not do this on a steep hill or if there is a lot of traffic where you may have to change lanes, etc.

When I started driving and cars had drum brakes all round, you had to be careful with them as they would easily overheat, but on a gentle hill or one where you don't need to brake very much, there is no problem with them on modern cars.

Silly question: should I decide to coast in neutral on a DSG, what happens if I'm dumb enough to accidently select reverse instead of drive? Are the electronics smart enough to ignore me?

I have noticed in our Fabia DSG that when travelling down hill, the gearbox actually drops one or two gears, this in effect improves engine braking.

 

 

Agreed. Mine does the same so there's actually no need to put it to N...

 

That's missing the point - the idea is to let it run free to save fuel. The question is the balance between zero fuel use when in 'D'  and less friction when in 'N'

 

On a related issue, my manual Mondeo I had before the Skoda did a steady 30 mph on a level road if you took your foot off the acceleartor in 6th gear, 25 in fifth and 20 in fourth. Damn disconcerting if you were going round a roundabout and found the car not slowing down!

Cant believe there are people actually doing this , coasting is pointless and you are not in full control of the car and therefore is illegal , not that you are likely you get caught.

Silly question: should I decide to coast in neutral on a DSG, what happens if I'm dumb enough to accidently select reverse instead of drive? Are the electronics smart enough to ignore me?

 

Reverse will engage and the outcome will depend on your speed and DSG box type. Worst case scenario is that the clutch will be burnt out or the box internals damaged, or you may just experience very rapid deceleration.

 

Reverse has the interlock that requires you to press the button on the selector, you can go between N and D without any need to press the button. Therefore the risk in selecting R is very minimal.

This is why I never use the button going between N and D when stopped. It means you can't accidentally knock it into R.

So technically you use more fuel coasting in N rather than D.

 

However going down a long hill on the motorway in N you can gain a bit of speed and travel further before having to use the gas again. Most of the time in D going down hill with your foot off the throttle the car looses speed unless it's really steep!

 

I do this now and then. I keep my hand poised on the gear lever. Would only take a split second to knock the lever back and engage drive should it be needed again.

 

My instant MPG readout goes to --- when coasting in N and I have had silly high trip MPG by doing this (once got over 68mpg with a calibrated trip computer).

 

Yes it's technically not the right thing to do but I wouldn't go as far as saying I'm not in control of the vehicle.

 

Another point to make is that the MK3 Octavia with DSG gearbox actually coasts automatically. If you lift off the accelerator in Eco mode the clutch is disengaged. I guess the VW bods have worked out it's more economical to coast and travel further than to coast in gear for less.

 

Phil

Edited 3 November, 201411 yr by Phil-E

I have had a quick look at highway code rule 122 that describes coasting. Would seem that the rule makes are not in favour but I don't read it as an expressly DO NOT DO. However as has been mentioned earlier its all to do with being in control of your car at all times, the code list some other car systems that may be affected by not having an engine speed appropiate to the speed of the vehical, extract pasted below:

122

Coasting. This term describes a vehicle travelling in neutral or with the clutch pressed down. It can reduce driver control because

• engine braking is eliminated
• vehicle speed downhill will increase quickly
• increased use of the footbrake can reduce its effectiveness
• steering response will be affected, particularly on bends and corners
• it may be more difficult to select the appropriate gear when needed.

My take on it is that for the negligable amount of fuel saved you will be needing to operate the clutch and gear box systems an additional two times. These systems will be obtaining their power from some where that must originate from the burning of fuel, there will also be additional wear on clutch components during operations, I know negligable amounts but thats what we're talking about here. I'm sure the brains at VAG will have looked at how to maximise the all important CO2 emitions and as mentioned before the new Octavias do seem to coast when appropriate - this system induced coast I'm sure will have been syncronised with the cars other systems so a not to reduce there effectivness and efficiency.

Reminds me of the "good old days" when cars were fitted with a freewheel!  (Saab 96 and some old Rovers for example)

Another point to make is that the MK3 Octavia with DSG gearbox actually coasts automatically. If you lift off the accelerator in Eco mode the clutch is disengaged. I guess the VW bods have worked out it's more economical to coast and travel further than to coast in gear for less.

My Subaru does this too. In Eco mode, it will coast for miles with my foot off the accelerator, in S and S# there is a noticable amount of engine braking. Its a nice feature.