Neutral

Aethelric · Post by **Aethelric** » Sat Mar 15, 2008 10:42 am

There was an interesting thread a few weeks ago about "drive or neutral" at lights. It got me thinking. Years ago I had a diesel astra which vibrated so much at tickover that I used to turn the engine off at the lights. When the lights turned, I'd push the clutch, and turn the key simultaneously. Warm diesels start virtually immediately so this introduced no delay.

With the Bongo, I've started to put it into neutral, and switch it off. When the lights change it's just a flick of the key then slip it into drive. It's early days, but I think this will have a significant effect on round town fuel consumption (not to mention air quality)

Anyone else do this?

Dave

Ralph · Post by **Ralph** » Sat Mar 15, 2008 10:56 am

You may loose more on starter replacement then you gain on fuel.

David Edwards · Post by **David Edwards** » Sat Mar 15, 2008 11:15 am

Yep plus it actually takes more fule and battery power to start up than leaving it running.

moonshine · Post by **moonshine** » Sat Mar 15, 2008 1:04 pm

Aethelric wrote:With the Bongo, I've started to put it into neutral, and switch it off. When the lights change it's just a flick of the key then slip it into drive.

Keep doing that Dave, and very soon you will have the fairly common Bongo problem of burnt starter motor contacts. When that happens, you will find that several turns of the key will just produce a click from the starter (and lots of honking from behind you) before finally it engages.

Aethelric · Post by **Aethelric** » Sat Mar 15, 2008 9:55 pm

David Edwards wrote:Yep plus it actually takes more fule and battery power to start up than leaving it running.

I don't think the battery power is significant.

Battery current to start is about 200A for less than 2 seconds (a hot engine will fire in a quarter of a revolution) which translates to 6amp minutes max, which is not a lot from a charged battery.
If we assume that the lights are left on when the engine is off, then that’s around 200W for say 30 seconds? So that’s another 8amp minutes.
So we'd lose around 15 amp minutes from the battery. That would be replaced very quickly when the engine starts.

As regards fuel, here is an interesting article:
http://www.eccj.or.jp/idstop/eng/dpeasts3.pdf

Starter motor wear may be an issue, although starting a hot engine will be a lot less strain than starting a cold one.

The starter motor contacts however will take the same inrush current hot or cold. I guess you are right moonshine.

BUT, if you take the argument further, this implies that the starter motor contacts have a predefined life in the number of starts they can perform before burnout. The vehicle is 12 years old and let’s say I am 75% (a figure plucked out of air) through that life time. So under normal operation I can get another 4 years out of them. If I operate in stop start mode, operations will go up by a factor of 3 so I only have a year left!
But if I put new contacts in now (cost around £20) I should get 5 years out of them. I don't have to save a lot of fuel to save £20 in 5 years.

Or I could be talking b.....ks of course.

francophile1947 · Post by **francophile1947** » Sat Mar 15, 2008 10:00 pm

Aethelric wrote:Or I could be talking b.....ks of course.

Very technical ones though

Seriously, I think the amount of fuel used, by an engine on tickover, is so low that it's not worth worrying about

The Great Pretender · Post by **The Great Pretender** » Sat Mar 15, 2008 11:15 pm

francophile1947 wrote:
Aethelric wrote:Or I could be talking b.....ks of course.
Very technical ones though
Seriously, I think the amount of fuel used, by an engine on tickover, is so low that it's not worth worrying about

Not in Wigan.
We have an 'Engineering dept'

that couldnt design its way out of a paper bag. 45% over tickover is the best you can expect here.

Like your thinking Aethelric, how about having a micro switch linked to the throttle pedal via a relay. Stopped for 30 sec engine switches off, press the throttle pedal engine starts?

Aethelric · Post by **Aethelric** » Sun Mar 16, 2008 12:13 am

francophile1947 wrote:
Aethelric wrote:Or I could be talking b.....ks of course.
Very technical ones though
Seriously, I think the amount of fuel used, by an engine on tickover, is so low that it's not worth worrying about

Well francophile, the Japanese study
http://www.eccj.or.jp/idstop/eng/dpeasts3.pdf
which used vehicles of a type comparable to bongos (2 litre diesels) showed an improvement of 15% on urban travelling - thats equivalent to decreasing your around town consumption from 23mpg tp 27mpg. That sounds good to me.
It does make me wonder how much of the difference in the consumption around town and on a long run is due time spent stationary at 0mpg.

BTW I believe switching off engines at lights etc is very common in europe - its mandatory in Switzerland.

Dave

carlioll · Post by **carlioll** » Sun Mar 16, 2008 9:17 pm

There are many things you can read from that report. It seems to be based on 47% of the driving time in urban areas the vehicle is stationary. Might be true in some major cities but for most of us this is way in excess of normal. It also states that re-starting the engine uses more fuel than leaving the engine idling for a short period. So personally, I dont hold any truck for this report -it is very ambiguous. I will continue to leave my vehicle in drive at traffic lights with the handbrake applied to stop creep as advocated by ROSPA

Aethelric · Post by **Aethelric** » Mon Mar 17, 2008 12:45 am

My previous tank full managed 180 km before the needle reached the half way point on the fuel guage. On my present tank full I have been stopping the engine at every opportunity. It's just reached the half way point at 210km.
OK, this is not scientific as trips may have been different (although most were around town and must have been at least similar) but it looks promising enough to make some proper measurements.

Carlioll, here is a quote from Ken Buchanan, an instructor with a top-level RoSPA (Royal Society for the Prevention of Accidents)
http://www.guardian.co.uk/environment/2 ... ortintheuk

Idling is the enemy - energy-burning at its most pointless and most toxic. Minimise it by rolling slowly to a stop in queues, and by switching off the engine where possible, mimicking hybrid cars, which automatically shut down during inactive periods. But don't bother slipping into neutral. A modern fuel-injected car coasting in neutral is basically idling in disguise and will consume more petrol than when it is in gear.

Its a relatively recent quote so either RoSPA is divided or has changed its advice.

Dave

francophile1947 · Post by **francophile1947** » Mon Mar 17, 2008 1:28 pm

Everybody knows that smooth driving and anticipation saves a lot of fuel. A diesel engined vehicle rolling to a halt, whilst in gear, uses no fuel at all. Therefore, with the correct anticipation, there is no need to switch the engine off, unless you are stopped for a long time.

carlioll · Post by **carlioll** » Mon Mar 17, 2008 4:49 pm

I agree -I think your driving style has a great influence on the mpg attained.

moonshine · Post by **moonshine** » Mon Mar 17, 2008 5:20 pm

Definitely. There is no point in racing up to lights, juntions, roundabouts etc. Drive smoothly and try to maintain as constant a speed as possible by slowing down when approaching red lights, and they will probably turn green by the time you get there, allowing you to continue without stopping. This saves much more fuel than racing up to the lights, coming to an abrupt stop, and accelerating away again, whether you turn the engine off or not. It gives your passengers a much more pleasant ride too.

Observation and the correct anticipation are the key to better driving, as my old PSV driving instructor used to say. More economical too, I wouldn't mind betting.

mikeonb4c · Post by **mikeonb4c** » Mon Mar 17, 2008 7:07 pm

Thinking 'out of the box' (yuk!) it is sometimes possible to reduce the journeys you do by x % . In my case I struck gold when I realised my journey to work was ideal for an electric bike. I've been saving £60 a month on fuel since last July. I then reallocate that £ at my discretion to do Bongo miles where it is happiest and most economical i.e. at 60-6mph heading for the great landscapes, with very few traffic lights

bigdaddycain · Post by **bigdaddycain** » Mon Mar 17, 2008 8:22 pm

I follow the "anticipation" school of thought with regards to economy myself...

If i'm feeling really economical,i'll restrict my revs to 2000 rpm,this makes a big difference to economy, but doesn't win you any friends from the following traffic when accelerating...

I quite like the idea of the micro-switch on the accelerator pedal to re-start after shut down.... hmm....

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