This VW DSG Coasting Function - who's tried it then?

[cptsideways]

So I've been given a new Passat for a few weeks, its a 6 Speed DSG Bluemotion, with a feature last seen on Saab's in the 1960's iirc, referred to the "Coasting Function" on the screen when it activates.

Very simply it freewheels in Neutral when you lift of the throttle. I've done about 1000miles in it this week & quite frankly I am astonished at just how far you can go with it.


Last night with the mother in law in the back so going gingerly for a change (I was picking her up from Bristol Airport) 80miles of hilly B Roads over the Mendips & we managed 76.6mpg all in all.

It takes some getting used to: For me, at least a week to master the technique & get used to that no deceleration on lift off feeling. Lots more anticipation required especially on motorways & I actively look for every bit of downhill possible & roundabouts are a new challenge all together

You can overide it by touching the brake pedal or stick it manual mode or apply throttle to re-engage the cogs.

[TheInternet]

cptsideways said:

So I've been given a new Passat for a few weeks, its a 6 Speed DSG Bluemotion, with a feature last seen on Saab's in the 1960's all manual cars, referred to the "Coasting Function"

[vrsmxtb]

I always thought coasting was a big no-no, and not actually of any benefit to fuel efficiency?

[anonymous-user]

cptsideways said:

Very simply it freewheels in Neutral when you lift of the throttle. I've done about 1000miles in it this week & quite frankly I am astonished at just how far you can go with it.

Why on earth would anybody want that?

[davepoth]

Symbolica said:

cptsideways said:

Very simply it freewheels in Neutral when you lift of the throttle. I've done about 1000miles in it this week & quite frankly I am astonished at just how far you can go with it.

Why on earth would anybody want that?

In a two stroke engine, such as fitted to the 1960s Saabs, the fuel lubricates the motor - so if you didn't have a freewheel it would seize up.

vrsmxtb said:

I always thought coasting was a big no-no, and not actually of any benefit to fuel efficiency?

True. The fuel injection will cut off entirely above around 1500rpm, so you use less fuel in that situation than you would with the engine in neutral. If it's a stop/start car I suppose it could be switching the engine off when it's in neutral, which would be best for economy.

[Regiment]

Why is it that if an automatic car does something, its a feature, but when a manual does it, it's just the way it works?

[ruff'n'smov]

We have enough problems with people using brakes to slow them slightly on a M'way without this.

MPG is impressive but few people will be bothered about it to master it.

No Thanks.

[mikey77]

Decades ago I had a Wartburg Knight with a 991cc three-cylinder two-stroke engine, with the same ancestry as the SAAB and a freewheel transmission. It took no time at all to get used to and still seems a great idea to me. You could, of course, lock the freewheel if needed to cope with bad weather, steep hills, or whatever.

[cptsideways]

Those of you familiar with hypermiling techniques will know that coasting instead of engine braking can be more efficient despite the fact the engine is running. I believe in the USA this feature also will stop the engine but not on this one unless I have not found the feature.

A modern eco diesel might only use 0.2L of fuel per hour so at 60 miles per hour in freewheel mode it is doing (goes off & does some schoolboy maths)........

300m per liter or 489km per liter or 1363.80 mpg & its not loosing momentum slowing down with engine braking

[AndyLB]

I think it's a good thing - yes, you have always been able to put a manual into neutral, but it's a bit of a chore to do it constantly throughout a journey.

Also, yes you get better mpg from being in gear when slowing down to a set of lights rather than in neutral (in neutral you'd probably use your brakes towards the end of the deceleration), but from 60 you would travel a lot further in neutral than you would in gear - so this isnt an appropriate comparison here.

[veevee]

cptsideways said:

freewheels... when you lift of the throttle.

cptsideways said:

80miles of hilly B Roads over the Mendips

[Caulkhead]

cptsideways said:

Those of you familiar with hypermiling techniques will know that coasting instead of engine braking can be more efficient despite the fact the engine is running.

How?

[Mastodon2]

I drive a Prius as a work car that has a similar function. You can change the dash display to a diagram of the car, showing you the wheels, the electric motor, the engine and the battery and where electricity is being used in the car. If you put the car in "Eco mode" (and you might aswell, as "Power mode" seems to give no more power, just worse MPG) and take your foot off the throttle, I'm pretty sure the gearbox disconnects as the MPG rating shoots up and the diagram shows the wheels generating power that goes back to the battery to recharge the battery on the move. It also has an "engine braking" position on the gear selector to give even more charging effect on long downhills.

So many features. Anything to take your mind off driving a Prius!

[cptsideways]

Caulkhead said:

cptsideways said:

Those of you familiar with hypermiling techniques will know that coasting instead of engine braking can be more efficient despite the fact the engine is running.

How?

Read the calculation I did above re coasting mpg with the engine running & decelerating but with no fuel used.

Deceleration puts all that kinetic energy back into turning the engine over which requires a lot of hp in reality

[off_again]

I am a big fan of the DSG gearbox and the advancements that VW have made. However, I am still not quite convinced that they quite as reliable as we might hope. A string of people I know have had big problems when the mileage is higher and they are very pricey to replace / refurbish.

Great idea, but I cant help thinking that more technology and features is decreasing reliability. What you save at the pump, you pay back in maintenance. Those who can afford a new car with a snazzy gearbox win, but those who cant afford anything better than a 5 year old car don't get the advantages. 5 years from now when people are picking these things up 3rd, 4th hand - I wonder how reliable they will be then....

[Caulkhead]

cptsideways said:

Caulkhead said:

cptsideways said:

Those of you familiar with hypermiling techniques will know that coasting instead of engine braking can be more efficient despite the fact the engine is running.

How?

Read the calculation I did above re coasting mpg with the engine running & decelerating but with no fuel used.

Deceleration puts all that kinetic energy back into turning the engine over which requires a lot of hp in reality

I still don't understand. When on the overrun no fuel is being injected into the engine. When coasting some fuel is being injected into the engine to stop it stalling. What am I missing?

[wolves_wanderer]

Caulkhead said:

cptsideways said:

Caulkhead said:

cptsideways said:

Those of you familiar with hypermiling techniques will know that coasting instead of engine braking can be more efficient despite the fact the engine is running.

How?

Read the calculation I did above re coasting mpg with the engine running & decelerating but with no fuel used.

Deceleration puts all that kinetic energy back into turning the engine over which requires a lot of hp in reality

I still don't understand. When on the overrun no fuel is being injected into the engine. When coasting some fuel is being injected into the engine to stop it stalling. What am I missing?

That the car uses little enough fuel to keep the engine running that the extra distance covered without the resistance of the engine and transmission makes it overall more efficient.

[philmots]

Caulkhead said:

I still don't understand. When on the overrun no fuel is being injected into the engine. When coasting some fuel is being injected into the engine to stop it stalling. What am I missing?

Because you can coast for aggeessss.

The technology has been on Volvo trucks for years and years.. I can be doing 50mph on a DC, turn off CC or let off throttle a full mile before a roundabout and it'll still be doing at least 20mph when I get there.

Go out in your car on a level bit of road and let your foot off in gear, then do the same in neutral, I wouldn't be surprised if you go twice as far. It more than makes up for the slight bit of fuel used to keep the engine ticking over.

You have to work with it (and understand it), though.. Else it'll just annoy you without any fuel saving benefit.

[cptsideways]

I'm off to do some research with the Torque app ..... back in a bit

[JordanTurbo]

Caulkhead said:

cptsideways said:

Caulkhead said:

cptsideways said:

Those of you familiar with hypermiling techniques will know that coasting instead of engine braking can be more efficient despite the fact the engine is running.

How?

Read the calculation I did above re coasting mpg with the engine running & decelerating but with no fuel used.

Deceleration puts all that kinetic energy back into turning the engine over which requires a lot of hp in reality

I still don't understand. When on the overrun no fuel is being injected into the engine. When coasting some fuel is being injected into the engine to stop it stalling. What am I missing?

It depends on what you are doing.

When deliberately slowing down staying in gear is more efficient as it uses no fuel and the engine braking effect is useful.

On the other hand, when you are trying to maintain speed and momentum (say cruising on the motor way) coasting when able to is better as the extra distance travelled out ways the small amount of fuel used. A stop start equipped vehicle could save even more fuel by switching the engine off when in coasting mode.

The VW system works in both of the above scenarios because it will not engage coasting mode if you press the brake pedal.