Start/stop on fuel efficiency?

Keep_pedalling

MataNui wrote: »

I wonder if the people posting who like it drive petrol cars? I found it really good on my petrol but its a pain on the diesel. The 3.0 diesel just doesnt crank as quickly or quietly. Plus it stops when i change from D to R which takes less than a second. I used to really like it on my last car but on this car turning it off is the first think i do when i start it.

Plus (and someone here may be able to correct me on this) i was told that diesels generate more soot on start. If thats true then it seems counter-productive (in terms of the DPF) to be doing lots more starts than is really needed.

Starting with a properly warmed up engine should not be a problem it's cold starts that are the real issue. Why your car does it moving between D & R seems a very strange arrangement.

https://link.springer.com/chapter/10.1007/978-3-319-15928-7_5

wymondham

Keep_pedalling wrote: »

Well no car knows how long the stop is going to be. If you know the stop is going to be very short then keep your foot on the clutch.

it would be good if the car paused for a few secs before switching off.....?

neilmcl

Keep_pedalling wrote: »

Starting with a properly warmed up engine should not be a problem it's cold starts that are the real issue. Why your car does it moving between D & R seems a very strange arrangement.

https://link.springer.com/chapter/10.1007/978-3-319-15928-7_5

And generally stop/starts are designed to work only once the engine is warmed up.

molerat

Keep_pedalling wrote: »

Well no car knows how long the stop is going to be. If you know the stop is going to be very short then keep your foot on the clutch.

wymondham wrote: »

it would be good if the car paused for a few secs before switching off.....?

I press the button on the dash to disable it if I am in stop start slow traffic.

IamNotAllowedToUseMyName

MataNui wrote: »

Had the feature on my petrol manual BMW. It was great on that car. Totally unobtrusive and started really quickly. Same cant be said for the feature on my diesel auto Jag XF. Its so bad i start every journey now by turning it off.

That's indicative of Jag engineering I'm afraid. Given that these days most of the manufacturers are using the same components they should be able to achieve the same quality of performance, the difference is down to poor implementation, e.g. quality of gear change.

Unobtrusive on my Mercedes C220Cdi. In fact, I've just had a battery go on me so stop start rarely kicked in and I missed it.

They do require a certain sympathy. There is no logic to waiting a few seconds before cutting out - if you do that, you miss those few seconds of opportunity and also you then may move off a second or two after that. Without a time machine, it is going to be difficult to predict.

On a manual, it is pretty easy to avoid an engine stop - for example, on the Audi, you simply don't raise the clutch in neutral, the days of taking neutral and applying handbrakes has long gone judging by the lack of cars without brake lights at a standstill. IOW, you pretty much are in control of when a stop can occur, an automatic is different, but as they tend to stop only when at a complete halt, for the situation where you can see you are barely going to stop, then a bit of anticipation and you can keep rolling - better not only for avoiding a stop/start but also minimising the acceleration required to get going again.

Mercdriver

IanMSpencer wrote: »

applying handbrakes has long gone judging by the lack of cars without brake lights at a standstill.

I think this is indicative of more automatics on the road. I have to admit that I rarely put the handbrake on at the lights, even now that I have the electric handbrake with the Mazda. Having said that, on damp nights at the lights I will put the handbrake on to ease the glare for the car behind

wymondham

molerat wrote: »

I press the button on the dash to disable it if I am in stop start slow traffic.

but if there was a short delay before the engine cut out then that would make this not needed... seems silly to have a stop/start system to save fuel and the planet and you have to press a button to turn it off as its not very clever...

System

So far everyone has commented on the pointless fuel saving but nobody has mentioned that an engine will destroy around 400 litres of atmosphere per litre of engine capacity, air we have to breathe to survive, for every minute that it is sat idling.

Richard53

Mercdriver wrote: »

Having said that, on damp nights at the lights I will put the handbrake on to ease the glare for the car behind

Thank you. Appreciated.

Gloomendoom

Tarambor wrote: »

So far everyone has commented on the pointless fuel saving but nobody has mentioned that an engine will destroy around 400 litres of atmosphere per litre of engine capacity, air we have to breathe to survive, for every minute that it is sat idling.

Humans "destroy" about 11,000 litres a day just idling. Maybe we should add a stop start feature.