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Saving fuel by stopping of engines in vehicles
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emordnilap



Joined: 05 Sep 2007
Posts: 11666
Location: way out west

PostPosted: Mon Feb 13, 2012 10:56 am    Post subject: Reply with quote

One fuel-related issue I would like some information on is stopping and starting a car engine. If you regularly encounter certain sets of traffic lights, you get an idea of when they'll change and whether it's worth turning off your vehicle engine.

It must be a trade-off involving factors such as the efficiency (in this case zero mpg!) of an engine and the amount of fuel needed to re-start the engine, combined with a good guess as to how long you will be stopped.

Is there any good way of calculating this for a range of vehicles? It's tied in with the number of vehicles I see with engines running and going nowhere, such as waiting outside a shop or the occupant on the phone.

I think it might have been from FOE where I read that if your vehicle is to be stationary for more than 30 seconds, turn the engine off - this must vary according to the factors above.
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mobbsey



Joined: 24 Nov 2005
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PostPosted: Mon Feb 13, 2012 12:14 pm    Post subject: Reply with quote

I've always heard that fine sand added tot he oil in the crank-case/gearbox can drastically reduce the fuel consumption of an engine.
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adam2
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Joined: 02 Jul 2007
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PostPosted: Mon Feb 13, 2012 12:20 pm    Post subject: Reply with quote

I too have heard that stopping the engine is worth it if expected to remain stationery for more than about 30 seconds.
In general, this seems sound advice, subject to the following caveats.

Dont stop the engine unless it has reached normal operating temperature, a cold engine may not re start readily and will suffer extra wear.

Dont stop the engine until it has run for long enough to fully charge the starter battery. If stopped for more than a few minutes, minimise battery discharge by turning headlights, heated windows, and heated seats off.
Modern vehicle batteries have a suprisingly low capacity.
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clv101
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PostPosted: Mon Feb 13, 2012 12:54 pm    Post subject: Reply with quote

adam2 wrote:
I too have heard that stopping the engine is worth it if expected to remain stationery for more than about 30 seconds.


The manual that came with my car (with a VW 130PD TDI engine) says that if stationary for 30-40 seconds, it uses less fuel to stop and restart then to idle.
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SleeperService



Joined: 02 May 2011
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Location: Nottingham UK

PostPosted: Mon Feb 13, 2012 4:00 pm    Post subject: Reply with quote

clv101 wrote:
adam2 wrote:
I too have heard that stopping the engine is worth it if expected to remain stationery for more than about 30 seconds.


The manual that came with my car (with a VW 130PD TDI engine) says that if stationary for 30-40 seconds, it uses less fuel to stop and restart then to idle.


When I lived in Germany it was an offence to be stopped for more than 30 seconds at a signal and leave your engine running. I think they are now fitting an automatic system to do it for you. As it was Germany you did it. DIN = das ist normal.

Never made aware of any reliability issues so maybe German market cars have bigger batteries fitted? There's usually spare space to fit a larger battery even on top spec UK diesel cars Confused

Girlie's 1.4 petrol SEAT has the same note in it's handbook BTW.
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PS_RalphW



Joined: 24 Nov 2005
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PostPosted: Mon Feb 13, 2012 4:15 pm    Post subject: Reply with quote

My diesel has automatic stop/start. Take the car out of gear and release the clutch and the engine stops, as long as

1. It has warmed up
2. The battery is sufficiently charged.
3. Not too much draw on the battery from lights, fans, etc.
4. The car is stationary...

Press the clutch and the engine starts, Takes about a second.

Works well, but I rarely get stuck in traffic where I am stationary for more than 10-20 seconds. It is no use in a typical jam with slow crawling traffic. If you can see far enough ahead in a jam to predict the next movement, it can be good. As I try to roll up to the back of a queue (and my car cuts all fuel to the engine when engine braking) and then maintain a steady 10mph crawl in second gear, the stop-start is rarely much of a plus.

Nice to have extra.
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JavaScriptDonkey



Joined: 02 Jun 2011
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Location: SE England

PostPosted: Mon Feb 13, 2012 9:04 pm    Post subject: Reply with quote

I remember reading that central government encouraged planners to consider traffic lights over roundabouts in order to increase the amount of fuel that was bought and so aid the Exchequer's income.

The best solution would be to turn most traffic lights off.

I have confidence that restarting a modern injection engine uses less fuel that idling it but they use very, very little when idling anyway so the gains will be minimal.

Offset against it will be increased wear in the starter motor and relays.

I think that the whole concept is just a ruse to get a few less gpm on the urban cycle figures for the sales blurb.
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ujoni08



Joined: 03 Oct 2009
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PostPosted: Mon Feb 13, 2012 9:36 pm    Post subject: switch off Reply with quote

I have got to know which lights on my commute take a long time, and always switch off the engine there, providing I have other clues about whether they have just turned red or not. A long queue in front of me normally means the lights have been red for quite a while. Traffic entering from the left (in one example I can think of) means the lights are in phase three, and about to turn green for me.

As I sit there in silence, I listen to all the other cars around me idling away, burning up fuel, and wonder if the drivers even think about it...
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emordnilap



Joined: 05 Sep 2007
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PostPosted: Mon Feb 13, 2012 9:42 pm    Post subject: Reply with quote

JavaScriptDonkey wrote:
The best solution would be to turn most traffic lights off.


Or just have one light, red, either on or off - a modern digital system where people don't have to think much.
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Tarrel



Joined: 29 Nov 2011
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Location: Ross-shire, Scotland

PostPosted: Tue Feb 14, 2012 12:01 pm    Post subject: Reply with quote

I began turning off my engine while idling years ago, when I was in "fuel sipping" mode during the 2000 fuel protests. I haven't measured the effect on consumption, but certainly find it's easy to do, and have never had any premature wear problems or trouble getting going.

It does amaze me how many folks go to the opposite extreme and idle their engines for ages. When I walk my dog in the morning, I pass a guy in a small van, sitting reading the paper with his engine running. He's still there 20 minutes later, when I come back, engine still running. No idea why.

My car has a fuel-burning heater that kicks in automatically below 10 degrees, to assist in warming the engine. The thinking is that the engine is so efficient that it takes a long time to warm up, thus reducing its efficiency because it would be running cold for a large proportion of the average short journey. The fuel-burning heater, although using fuel itself, mitigates against this.

Apparently you can retro-fit them. They are made by Webasto.
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emordnilap



Joined: 05 Sep 2007
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Location: way out west

PostPosted: Tue Feb 14, 2012 1:16 pm    Post subject: Reply with quote

Tarrel wrote:
a guy in a small van, sitting reading the paper with his engine running. He's still there 20 minutes later, when I come back, engine still running. No idea why.


I am amazed at the number of people who do this; maybe it's a more common mindset of this side of the isles. It's default behaviour, to not consider energy wastage.

It could be worked out what any particular idling vehicle is consuming in energy doing zilch and what energy I use to cycle to work. It would probably be an interesting comparison.
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RenewableCandy



Joined: 12 Sep 2007
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PostPosted: Tue Feb 14, 2012 4:44 pm    Post subject: Reply with quote

He probably wants to appear "dynamic" Rolling Eyes . Or perhaps, this time of year, just to keep warm.
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Tarrel



Joined: 29 Nov 2011
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Location: Ross-shire, Scotland

PostPosted: Tue Feb 14, 2012 4:53 pm    Post subject: Reply with quote

He certainly doesn't look very dynamic, and as for keeping warm, tough s***; he should put another layer on.

There's another one on a (different) dog-walking route. Woman who drives her kid to the bus stop to wait for the (private) school bus. She sits there and waits with him in the car, engine running, until the bus comes. Rolling Eyes
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emordnilap



Joined: 05 Sep 2007
Posts: 11666
Location: way out west

PostPosted: Tue Feb 14, 2012 5:33 pm    Post subject: Reply with quote

Tarrel wrote:
Woman who drives her kid to the bus stop to wait for the (private) school bus. She sits there and waits with him in the car, engine running, until the bus comes. Rolling Eyes


There's school near here where that happens but there's usually at least half a dozen of them burning money!

Now, for an individual, it's not a lot of fuel. But this is going on, to some degree, planet-wide.
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Tarrel



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PostPosted: Tue Feb 14, 2012 5:37 pm    Post subject: Reply with quote

One wonders how high the fuel price has to go, to prompt a change in behaviour. You'd have thought £1.40 a litre was enough!
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