Start/stop on fuel efficiency?

Adly812

I have the start/stop feature. And I'm interested to know how it should be used on fuel efficiency. I totally see the sense in using it when your stationary in a jam, road works etc. But when you're just at the traffic lights, surely restarting the engine would use more fuel than just keeping it idle for 30 seconds?? What's the minimum wait time that would prove beneficial when activating it?

BeenThroughItAll

Smb3088 wrote: »

I have the start/stop feature. And I'm interested to know how it should be used on fuel efficiency. I totally see the sense in using it when your stationary in a jam, road works etc. But when you're just at the traffic lights, surely restarting the engine would use more fuel than just keeping it idle for 30 seconds?? What's the minimum wait time that would prove beneficial when activating it?

No such thing, modern fuel injected engines don't use loads of fuel at startup, otherwise catalytic converters would be ruined five minutes after they rolled out of the showroom.

At any time in a modern car, having the engine not running is more fuel efficient than having it running.

That's not to talk about additional wear on other components, however.

Alter_ego

Also consider the reduction in pollution.

arcon5

The ecu is programmed to manage what and when conditions are adequate to activate stop start. You shouldn't need to. For example if the engines cold it won't come on as it will offer no benefits to economy or emissions as the engine to needs reach temp

chrisw

As a rough guide, my diesel Volvo car says it's using 0.1 gallons per hour idling, which is about 53p per hour.

So allowing it to idle costs about 1p per minute in fuel.

thescouselander

chrisw wrote: »

As a rough guide, my diesel Volvo car says it's using 0.1 gallons per hour idling, which is about 53p per hour.

So allowing it to idle costs about 1p per minute in fuel.

Interesting calculation. My car tells me the stop start has been active for a total of 25 hours since it was new. On that basis I've saved just over £13. I've no doubt that all the extra engineering needed to implement stop start cost a lot more than that - the whole thing seems like a waste of time to me.

RichardD1970

thescouselander wrote: »

Interesting calculation. My car tells me the stop start has been active for a total of 25 hours since it was new. On that basis I've saved just over £13. I've no doubt that all the extra engineering needed to implement stop start cost a lot more than that - the whole thing seems like a waste of time to me.

It has only ever been about the manufacturers reaching emissions targets, not saving the motorist money.

IamNotAllowedToUseMyName

In terms of pollution and economy, then stop start comes into its own in a few seconds. Some manuals will cut out at low speed while still coasting to a halt. Oddly, to make stop/start work mainly is a few tweaks to make the cars start quickly and reliably - my diesel barely cranks on a restart, which makes me wonder why all cars are not engineered to start so easily.

The only real extra cost is a higher spec battery once they've gone down the stop start route. The rest is mainly tuning and a bit more care in component selection and some software. Merc, for example, had a semi-automatic starting system back in the 1990s, where the car determined whether the engine had successfully started so it controlled the cranking until that point.

I suspect at rush hour, stop start could make quite a large impact on pollution in cities, my journeys less so, as I avoid heavy traffic times where possible.

iltisman

I walk past lots of cars waiting at traffic lights and I notice the stop/start cars are slower at getting moving . This must make the jams worse.
The starting must drain the battery of capacity that will have to be replaced by the alternator using more fuel.

IamNotAllowedToUseMyName

iltisman wrote: »

I walk past lots of cars waiting at traffic lights and I notice the stop/start cars are slower at getting moving . This must make the jams worse.
The starting must drain the battery of capacity that will have to be replaced by the alternator using more fuel.

Starting a stop/start car should be very easy and is not a massive drain on the battery. Mine uses the alternator to do some recharging on braking as well.

In terms of getting going, there is minimal delay in an automatic, and I can certainly pull away from a junction into any gap that I would without stop start - there may be a momentary anticipation.

Other advantages - our manual Q3 is certainly no delay because you restart by depressing the clutch, so the normal restart process covers any supposed delay of stop start. Another bonus is that contrary to experience elsewhere, the Q3 is quite easy to stall at low speed in second and it auto-restarts simply by dipping the clutch, so you soon can recover.

Stop-start does need you to adjust your technique, and it seems to me that many drivers are disinterested in driving, and that is what leads to trouble - they want to drive as if they are still in a 1980s Cavalier - the sort of people who complain that they break speed limits because you can't drive at 30mph in 6th.

boliston

My oh's car has stop start and i find it encourages better driving technique such as properly stopping and using the handbrake instead of just using the foot brake once stopped. Also it also discourages the habit of "creeping" in slow moving traffic - i tend to wait till a worthwhile gap has opened up in front before moving off instead of just creeping a couple of metres then stopping, which just wastes fuel.