Does stop start really save fuel or just cut down emissions?

[monkeyhanger]

Thanks monkeyhanger.  I have a DSG which sadly means it stops the engine every time I stop, unless I deactivate the system.

I still think it would be better if it stopped after so many seconds of idling, rather than straight away 

Ian

That is one of the best things about a manual – stopping the car thinking for you. You can decide if you want the car to stop or not, by use of the clutch. Also, when the car has cut out after stopping and you can see when traffic starts to move ahead of you, or know when a set of lights is about to change to green for you (as the other directions have gone to amber or red on a crossing etc), you can dip that clutch and get the car started to move straight off. That second or so of pressing the accelerator on a DSG and waiting for the car to start up again is really annoying (for me anyway) as it feels so much longer when you want to move off at a busy roundabout etc. My dad disables his stop-start on his DSG GTD every journey for the reasons above (although his commute has very few stops).

Having the car wait and then cut out might not be the answer. If you have it cut out after 10 seconds, and you’re waiting say a minute anyway, that’s 10 seconds the car could have been saving fuel. If on the other hand, it waits 10 seconds and then cuts out on what would have been a 15 second stoppage at lights, I’d find that annoying.

I think the best way for you to have “selective stop-start” would be to disable the system with the button as you can right now, but have a button on the steering wheel to action the engine cut-out, working only when the car is stationary. Car would fire up again as per normal with the accelerator pedal on DSG. Doesn’t work with manual, the car will never start or restart unless you dip the clutch, so we’d carry on as I already do.

[jivemonkey]

Thanks monkeyhanger.  I have a DSG which sadly means it stops the engine every time I stop, unless I deactivate the system.

I still think it would be better if it stopped after so many seconds of idling, rather than straight away 

Ian

That is one of the best things about a manual – stopping the car thinking for you. You can decide if you want the car to stop or not, by use of the clutch. Also, when the car has cut out after stopping and you can see when traffic starts to move ahead of you, or know when a set of lights is about to change to green for you (as the other directions have gone to amber or red on a crossing etc), you can dip that clutch and get the car started to move straight off. That second or so of pressing the accelerator on a DSG and waiting for the car to start up again is really annoying (for me anyway) as it feels so much longer when you want to move off at a busy roundabout etc. My dad disables his stop-start on his DSG GTD every journey for the reasons above (although his commute has very few stops).

Having the car wait and then cut out might not be the answer. If you have it cut out after 10 seconds, and you’re waiting say a minute anyway, that’s 10 seconds the car could have been saving fuel. If on the other hand, it waits 10 seconds and then cuts out on what would have been a 15 second stoppage at lights, I’d find that annoying.

I think the best way for you to have “selective stop-start” would be to disable the system with the button as you can right now, but have a button on the steering wheel to action the engine cut-out, working only when the car is stationary. Car would fire up again as per normal with the accelerator pedal on DSG. Doesn’t work with manual, the car will never start or restart unless you dip the clutch, so we’d carry on as I already do.

Not entirely true, as mentioned previously there is a somewhat selective start stop procedure that you can do in the DSG which I do every trip and now do as second nature. If I know that I'm going to be stopped only briefly, I will not apply full pressure to the brake and I'll take my foot off as soon as the auto hold takes..hold. The engine will keep on ticking over happily. If, for some reason, I don't get a chance to move as I initially thought I'll go ahead and press the brake again for a couple of seconds and the engine cuts out. As it's DSG, point of note that this won't make you look like a looney from behind flashing your brake lights, these are already on from the auto hold system. Once I see cars ahead moving or the lights change, I just 'blip' the accelerator and she fires up. Auto hold remains active and I can move off smoothly and promptly as and when required.

Works like a charm. 

[iandjm]

Thanks monkeyhanger.  I have a DSG which sadly means it stops the engine every time I stop, unless I deactivate the system.

I still think it would be better if it stopped after so many seconds of idling, rather than straight away 

Ian

That is one of the best things about a manual – stopping the car thinking for you. You can decide if you want the car to stop or not, by use of the clutch. Also, when the car has cut out after stopping and you can see when traffic starts to move ahead of you, or know when a set of lights is about to change to green for you (as the other directions have gone to amber or red on a crossing etc), you can dip that clutch and get the car started to move straight off. That second or so of pressing the accelerator on a DSG and waiting for the car to start up again is really annoying (for me anyway) as it feels so much longer when you want to move off at a busy roundabout etc. My dad disables his stop-start on his DSG GTD every journey for the reasons above (although his commute has very few stops).

Having the car wait and then cut out might not be the answer. If you have it cut out after 10 seconds, and you’re waiting say a minute anyway, that’s 10 seconds the car could have been saving fuel. If on the other hand, it waits 10 seconds and then cuts out on what would have been a 15 second stoppage at lights, I’d find that annoying.

I think the best way for you to have “selective stop-start” would be to disable the system with the button as you can right now, but have a button on the steering wheel to action the engine cut-out, working only when the car is stationary. Car would fire up again as per normal with the accelerator pedal on DSG. Doesn’t work with manual, the car will never start or restart unless you dip the clutch, so we’d carry on as I already do.

Not entirely true, as mentioned previously there is a somewhat selective start stop procedure that you can do in the DSG which I do every trip and now do as second nature. If I know that I'm going to be stopped only briefly, I will not apply full pressure to the brake and I'll take my foot off as soon as the auto hold takes..hold. The engine will keep on ticking over happily. If, for some reason, I don't get a chance to move as I initially thought I'll go ahead and press the brake again for a couple of seconds and the engine cuts out. As it's DSG, point of note that this won't make you look like a looney from behind flashing your brake lights, these are already on from the auto hold system. Once I see cars ahead moving or the lights change, I just 'blip' the accelerator and she fires up. Auto hold remains active and I can move off smoothly and promptly as and when required.

Works like a charm. 

Will be trying this tonight

[Sootchucker]

Exactly, I can decide very easily if I want the engine off or not at standstill by modifying my brake pressure. Really easy to do and works every time. As jivemonkey said, as soon as the green Auto-hold light comes on, take your foot off the brake, and the engine will continue to run.

After a short while, you won't even need to look at the dash as the required pressure will become second nature. I can do it 100% of the time if I wish.

As to the comments above over the Stop / Start system components, I found this for a 2010 VW Self Study Manual, which explains the component changes made to incorporate S/S.

It was possible to create the start/stop system 2009 with only a few new components. These include the battery monitor control unit J367 and the start/stop operation button F416.
It was, however, also necessary to adapt some components, for example, the starter motor and the alternator for use with the start/stop system. You will find examples of components and systems that have been adapted for BlueMotion use in the following list.

Control units (general) -  Program code of control units expanded by one information bit for the start/stop system
(concerns control units that act on the start/stop system or are influenced by it.)

Alternator - LIN connection to the diagnosis interface for data bus

Battery - Absorbent glass mat battery to increase cyclical resistance

Starter - Special Higher wear resistance

Vehicle electrical system - Battery monitoring via a separate battery sensor on the minus pole of the absorbent glass mat battery - New battery wiring,  - Battery monitor control unit connected to the data bus diagnostic interface via LIN data bus

Manual gearbox Gear detection sensor G604 - currently: sensor with analogue signal output - planned from calendar week  2/09 as sensor with pulse width modulated signal output

[monkeyhanger]

The “soft stop” option isn’t always possible – if someone slams on their brakes in front of you and you have to do likewise, or if you’re heading towards a set of lights at a bit of speed and they change, you realise you won’t make it through on green/amber and have to brake harder than you otherwise might, someone does something unexpected and causes you to brake etc. Making a split second decision and jumping on the brakes, usually doesn’t allow you to come off right at the end to a soft stop and not engage the stop start. The disablement and an override button to switch off would be infallible in that respect.

[corgi]

In answer to your original question.

It depends. If a significant proportion of your driving is in heavy traffic the potential benefits are worth having as Moneyhanger very eloquently described earlier. In the end the use of fuel is directly related to emissions... if the engine's not running then there are no emissions. Monkeyhanger is, of course, correct to observe that these systems have become more prevalent since the change in the standard fuel consumption tests in the EU.

There must be a point where letting the engine run whilst stopped vs letting the stop/start kick in... I'm sure I read somewhere that BMW reckon that if you are stopped for more than 4 seconds there is a benefit in letting the stop/start kick in... less than that, let it tick over...

[p3asa]

There must be a point where letting the engine run whilst stopped vs letting the stop/start kick in... I'm sure I read somewhere that BMW reckon that if you are stopped for more than 4 seconds there is a benefit in letting the stop/start kick in... less than that, let it tick over...

I googled that a while back and there are all sorts of times suggested. 4 seconds all the way to 30 seconds. Although I found 7 seconds mentioned quite a bit.

I always thought starting a car took more fuel than it idling but not according to this motoring site
http://www.caranddriver.com/features/engine-stop-start-systems-explained-tech-dept

[monkeyhanger]

Stop-start is great for reducing the official emissions for tax purposes, if nothing else. For the average non-city driver, real world results are far less dramatic. My GTD is causing as much pollution as my Scirocco in real world use, but I get to give the government £105 less car tax, it’s like legalised tax evasion. Can’t be too long until the Government/DVLA put a stop to it.