how much fuel used in idle mode

Ultrasonic

daveyjp wrote: »

No, if the engine stops because stop start is working the engine will be off. To prevent me getting out and leaving a car which could start up on its own the engine restarts as soon as the seatbelt is removed from the buckle, alerting the driver that the engine needs switching off properly.

Surely it could alert you with some sort of sound rather than actually starting the engine? That seems like a bit of a waste of fuel! There's probably a good engineering reason for why it's done this way though...

mutley74

Ultrasonic wrote: »

Do you possibly mean dipped to sidelights? If not, you shouldn't have full beam on in a queue of traffic anyway, not just to save fuel.

I never do....

Richard53

Ultrasonic wrote: »

Nonsense, see posts above. Fuel use is low but certainly not negligible. Just do some city driving and watch trip mpg drop while you are stationary. If it was as miniscule as you suggest there is no way car manufacturers would have gone to the huge expense and trouble to create complicated start-stop systems.

I don't think we are disagreeing here. You measured 0.14 gph while idling - that's a gallon for every seven hours' idling. In my view, that is a tiny amount, although you could disagree with my interpretation.

And I did say that there would be little benefit unless all your driving was stop/start in the city. I can see it being a worthwhile facility on a city car. Assuming a one hour city commute where 20% of the journey time was sitting idling in a queue, you would save 0.14/5 gallons per journey by having the engine off when the car was stationary. That's .013 litres, or about 18p worth. Small, but not insignificant.

On a motorway or A-road journey, the benefit would be minuscule.

Ultrasonic

mutley74 wrote: »

I never do....

You said:

mutley74 wrote:

If I am waiting in a heave traffic queues (unless its very dark) I usually turn my headlights from full beam to dipped level to reduce engine demand.

I thought you'd just mis-typed to be honest. Even approaching a queue with main beam on would be inconsiderate.

Ultrasonic

Richard53 wrote: »

I don't think we are disagreeing here...

OK, but to suggest idle fuel consumption is so low you could only detect it with specialist lab equipment is overstating it. We've also been talking about diesel idle figures, the effect will be bigger for petrol cars.

Obviously for long motorway driving with no idling a stop-start system will be of no use. But I would suggest that the majority of commuters spend a not insignificant part of each trip stationary so I don't think stop-start is a completely stupid idea. And I'm not just talking about people living in big cities here.

Not that I'll be rushing to buy a car with it. I'd still be worried that it would end up causing more trouble than it's worth!

Ultrasonic

Richard53 wrote: »

Assuming a one hour city commute where 20% of the journey time was sitting idling in a queue, you would save 0.14/5 gallons per journey by having the engine off when the car was stationary. That's .013 litres, or about 18p worth. Small, but not insignificant.

Obviously a typo, but you meant 0.13L. For a 5 day a week, 48 week working year that would be a total of 61L of wasted fuel. Your 20% stationary example is perhaps a bit extreme but this to me still shows a fair amount of fuel wasted. (I'm interested in this from an environmental point of view as well as a financial one by the way.)

More modern cars probably manage to use less fuel at idle than mine as well of course.

Richard53

Ultrasonic wrote: »

OK, but to suggest idle fuel consumption is so low you could only detect it with specialist lab equipment is overstating it.

You're probably right. It wouldn't be the first time.

Ultrasonic wrote: »

Not that I'll be rushing to buy a car with it. I'd still be worried that it would end up causing more trouble than it's worth!

My thoughts exactly. For one, hearing the starter motor strike up every few minutes instead of once per journey made me wonder about its longevity, and for another, it struck me that the system only works as it should when the engine is in 100% tune, the battery perfect, and so on. The kind of gradual deterioration that all cars suffer, and which the driver can easily adapt to over time, could end up being a show-stopper in the middle of a traffic jam if you were unlucky.

Ultrasonic wrote: »

Obviously a typo, but you meant 0.13L.

Just checking you were paying attention

Yes I did, thanks.

mutley74

Richard53 wrote: »

You're probably right. It wouldn't be the first time.



My thoughts exactly. For one, hearing the starter motor strike up every few minutes instead of once per journey made me wonder about its longevity, and for another, it struck me that the system only works as it should when the engine is in 100% tune, the battery perfect, and so on. The kind of gradual deterioration that all cars suffer, and which the driver can easily adapt to over time, could end up being a show-stopper in the middle of a traffic jam if you were unlucky.



Just checking you were paying attention

Yes I did, thanks.

guess in such situation (traffic) probably best to disable the s/s system

I meant I switch from full mean to side lights in queues

WTFH

Richard53 wrote: »

it struck me that the system only works as it should when the engine is in 100% tune, the battery perfect, and so on. The kind of gradual deterioration that all cars suffer, and which the driver can easily adapt to over time, could end up being a show-stopper in the middle of a traffic jam if you were unlucky.

Which is when it wouldn't STOP.
Remember, it stops before it has to try to restart, so it won't stop if the battery charge and the drain on it are at a level which means it won't be able to start it again.

As for starter motors failing, yes, that would be true if the engineering behind start/stop and the mechanics used were identical to cars which don't have it fitted. As far as I'm aware, they aren't

Richard53

mutley74 wrote: »

guess in such situation (traffic) probably best to disable the s/s system

So the one time the system is potentially of benefit is the time you disable it?