02GF74
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| posted on 23/9/14 at 08:37 PM |
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stop start - does it save fuel
Or is it a gimmick?
Starting a car takes a fair bit of juice out the battery that is then recharged thus needing more fuel.
idling uses fuel as does having to charge the battery, for how long does a car need to be stationary with engine off before savings are made?
[Edited on 24/9/14 by 02GF74]
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JoelP
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| posted on 23/9/14 at 09:05 PM |
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A warm engine will restart very easily. In traffic I imagine the saving adds up nicely. It also helps keep your emissions down when assessing your
road tax.
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David Jenkins
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| posted on 23/9/14 at 09:11 PM |
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I'm not convinced - my Yaris has this and, apart from being an annoying 'feature', the car has an enormous battery that's
about twice the size of the one fitted to my old Yaris that didn't have this functionality. Think of the difference in battery size between
petrol and diesel cars and you'll understand just how big this battery is.
tl/dr: It may save fuel while sitting in traffic, but I have the extra weight of a huge battery to lug about.
Forgot to mention - if I've got the air conditioning on the engine only stays stopped for 30 seconds or so... so fairly pointless, really.
[Edited on 23/9/14 by David Jenkins]
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mark chandler
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| posted on 23/9/14 at 09:20 PM |
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I believe it's more about emmisions targets being met when being averaged out so better economy is a bonus.
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britishtrident
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| posted on 23/9/14 at 09:44 PM |
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The problems will come when these vehicles reach high mileages.
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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SteveWalker
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| posted on 23/9/14 at 09:58 PM |
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Are these stop-starts using "normal" starters?
I saw a design some years ago that used a toothed ring inside the bellhousing and teeth on the flywheel to act as an alternator when running and as a
variable reluctance motor when starting, thus having no meshing teeth and no wear to the starter mechanism. I would have thought standard style
starters and ring-gears would be prone to early failure with stop-start.
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NigeEss
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| posted on 23/9/14 at 10:49 PM |
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But when your starter and/or alternator fails early due to excessive use, there's a big chunk of
your savings down the Swanee.
Time is an illusion. Lunchtime doubly so.................Douglas Adams.
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britishtrident
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| posted on 24/9/14 at 07:05 AM |
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quote:
Originally posted by NigeEss
But when your starter and/or alternator fails early due to excessive use, there's a big chunk of
your savings down the Swanee.
Yes on some cars changing the starter or alternator requires a lot of man-hours.
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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garyo
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| posted on 24/9/14 at 11:10 AM |
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As others have suggested, an 'energy saving' target is different to an emissions target. Modern generation diesels are a good example of
this, where total MPG has been sacrificed to drive EGR and DPF systems. I suppose it's especially relevant in town centres.
Up until now the individual motorist used to reap the rewards of energy saving... but you've got to tread carefully now.
[Edited on 24/9/14 by garyo]
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loggyboy
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| posted on 24/9/14 at 11:50 AM |
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Remember these eco systems are aimed at ticking boxes, to save on road tax and company car tax and mpg figures. The wear on any components wont worry
initial owners as they have warranties and by the time they filter down the super used market the manufacturer can wash their hands of them. (or rub
them together with the added work the repairs will generate).
Mistral Motorsport
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SCAR
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| posted on 24/9/14 at 12:08 PM |
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Nothing new. In 1975 I had a mk1 Cortina that used to stop every time I pulled up
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Mr Whippy
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| posted on 24/9/14 at 12:50 PM |
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Every time I hear one of these car start up, I can't help thinking how much wear that's adding to the starter motor and the flywheel
teeth, plus the oil pressure has to build up all over again each time. Surely about the worst thing you could do to an engine’s life span.
As above, have you seen the size the start stop batteries? There massive things and there twice the price too.
Ok if you’re sat in a huge tail back switch off the engine but for a 3 minute traffic light cycle get real, it must save a few mil of petrol. Everyone
I know who has it on their cars can’t stand the feature and turn it off. I’m so glad my car is too old to have any emission garbage on it and I still
get 45mpg 
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hughpinder
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| posted on 24/9/14 at 12:56 PM |
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My belief is that it is mainly useful on the 'test cycle' that determines your cars CO2 rating.
This gives some savings in road tax, but by far the most important is the saving in company car tax.
The last 3 BMWs my missus has had as company cars all have the feature, and we have tried switching it off, with no discernable difference in mpg (her
car does 800+ miles a weeks so you would spot it if it were more than 0.2mpg).
I don't believe most engines are tuned well enough to notice that the alternator is charging the battery, compared to not charging it - you
don't see big mpg differences running with your lights on all winter(say 200W continuous for front/rear/side lights), compared to summer
running. The alternator is regulated to something like 50-70A, which is only 800 odd watts at 14V. Don't forget that the start current for an
engine is much less once it has warmed up, and fuel injection only gives the fuel required for the current engine temperature.
On another point, I had a honda civic which I converted to LPG and ran for 207K, during which time it stopped every time I forgot to blip the throttle
as I reached a junction or roundabout, so it probably had at least 100K starts from a normal starter without failing (or needing a special battery or
alternator replacement).
Regards
Hugh
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britishtrident
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| posted on 24/9/14 at 01:26 PM |
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quote:
Originally posted by SCAR
Nothing new. In 1975 I had a mk1 Cortina that used to stop every time I pulled up
Fords of that era saved even more fuel by not starting on a cold morning.
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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britishtrident
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| posted on 24/9/14 at 01:31 PM |
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quote:
Originally posted by hughpinder
My belief is that it is mainly useful on the 'test cycle' that determines your cars CO2 rating.
This gives some savings in road tax, but by far the most important is the saving in company car tax.
The last 3 BMWs my missus has had as company cars all have the feature, and we have tried switching it off, with no discernable difference in mpg (her
car does 800+ miles a weeks so you would spot it if it were more than 0.2mpg).
I don't believe most engines are tuned well enough to notice that the alternator is charging the battery, compared to not charging it - you
don't see big mpg differences running with your lights on all winter(say 200W continuous for front/rear/side lights), compared to summer
running. The alternator is regulated to something like 50-70A, which is only 800 odd watts at 14V. Don't forget that the start current for an
engine is much less once it has warmed up, and fuel injection only gives the fuel required for the current engine temperature.
On another point, I had a honda civic which I converted to LPG and ran for 207K, during which time it stopped every time I forgot to blip the throttle
as I reached a junction or roundabout, so it probably had at least 100K starts from a normal starter without failing (or needing a special battery or
alternator replacement).
Regards
Hugh
Older Hondas were designed not to fail until they reach at least their 12th birthday, then one part will fail and within a week at least 4
unrelated items will break/burn-out/fall off or just crumble into dust.
Back to fuel saving with an OBD II scanner on you can see the percentage engine load at idle jump up from say 2 percent to 4 percent when the AC,
heater blower or head lights are turned. Modern cars to prevent stalling have connections from the engine ECU to the AC and power steering which
open the idle speed control valve a fraction more when they are activated.
[Edited on 24/9/14 by britishtrident]
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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mcerd1
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| posted on 24/9/14 at 01:45 PM |
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the few hire cars I've driven recently all had it, I just found it irritating
I found that half the time it stops the engine just as your ready to go again, especially driving in a busy town - in which case it probably cost more
fuel that it saved 
my rather thirsty tin-top claims to use between 0.2 and 0.3 gallons and hour when idling (which my maths says is 15 to 23ml/min) so if that even half
true you'd hardly save much with a start-stop
quote:
Originally posted by Mr Whippy
I’m so glad my car is too old to have any emission garbage on it and I still get 45mpg
the 106 I sold to mango used to get me 37mpg despite doing mostly short but 'enthusiastic' drives around the back roads
or if I was a bit more gently it would give 42mpg on the back roads and 62mpg on the motorway
and that's with 4 gears, a single choke solex carb and a manual choke !
[Edited on 24/9/2014 by mcerd1]
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hughpinder
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| posted on 24/9/14 at 02:48 PM |
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Originally posted by britishtrident
Quote:
"Older Hondas were designed not to fail until they reach at least their 12th birthday, then one part will fail and within a week at least 4
unrelated items will break/burn-out/fall off or just crumble into dust."
Made me laugh because thats pretty much exactly what happened - about 10 (expensive) things failed when it was 12 years old - luckily all within about
2 weeks so I hadn't got round to buying any bits/arranging for it to be fixed before I decided to scrap it.
Although I believe you when you that the idle valve opens slightly when the lights are on etc, I haven't seen that produce a noticible effect on
the final fuel consumption, dispite the fact that in the winter I probably have all the lights on, rear screen heater on, blower to the screen, wipers
on and probably aircon while the screen clears. I thinks it may affect very tightly set up eco cars, but I haven't really seen a difference in
'normal' cars. Is this similar to the original question - you can see somethings happened that should increase or decrease fuel use, but
practically there is no significant change? Most of my driving is down back lanes where you are accelerating or braking almost all of the time, rather
than running at a fixed speed where you may get to back off to minimum throttle so I guess that affects my viewpoint.
Regards
Hugh
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Slimy38
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| posted on 24/9/14 at 03:47 PM |
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It's a shame that increase idle feature didn't come in earlier. My old 1.2 Nova would stall if you had the lights and the rear heater on,
I had to pull the choke out a little to keep it running.
Although on that subject, only one of my current circle of friends knows what a choke is/was... I'm assuming it's a much higher ratio of
knowledgeable people on here!
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mcerd1
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| posted on 24/9/14 at 04:13 PM |
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quote:
Originally posted by Slimy38
Although on that subject, only one of my current circle of friends knows what a choke is/was... I'm assuming it's a much higher ratio of
knowledgeable people on here!
my first 2 cars both had manual chokes and I'm not that old either... I only got a car with this modern EFI stuff in 2008
my mates used to laugh at them - until mine was the only one that started first time at -15°C 
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beaver34
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| posted on 24/9/14 at 04:42 PM |
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stop start cars use different starter motors that are up to the job, i dont think they are any less reliable than normal units
for a focus from 2011 onwards the whole north of England from Birmingham north to Scotland used 9 starter motors last year and 20 this year.
the standard non stop start unit has used 14 so far this year.
what is worrying is that after a while stood still the car restarts on its own and catches you off guard, i thought the car was going to set off on
its own!
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02GF74
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| posted on 24/9/14 at 07:07 PM |
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Hmmmm general consensus seems there is negligible fuel saving.
It has been said that a warm enginr is easier to start than s cold one but i would imagine most peoples commutes are like mine, first .5 mile is 20
mph, the next mile is stop start, mostly stop the remaining 2 milrs at 30 mph.
So in winter, the engine will not have time to warm up anf being stationary with it off aint gonna warm it up.
One would think a spinning fly wheel instead of electric starter could be used.
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beaver34
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| posted on 24/9/14 at 09:34 PM |
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quote:
Originally posted by 02GF74
Hmmmm general consensus seems there is negligible fuel saving.
It has been said that a warm enginr is easier to start than s cold one but i would imagine most peoples commutes are like mine, first .5 mile is 20
mph, the next mile is stop start, mostly stop the remaining 2 milrs at 30 mph.
So in winter, the engine will not have time to warm up anf being stationary with it off aint gonna warm it up.
One would think a spinning fly wheel instead of electric starter could be used.
Stop start only works once engine temp is at normal temp and also that battery voltage is above normal, so on a short comute in a diesel it will not
turn off
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morcus
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| posted on 24/9/14 at 09:49 PM |
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I've got a mate who reckons he gets more MPG from his Astra with stop start, also I was under the impression a lot of the systems did use some
sort of flywheel method rather than a starter motor. I've never driven a car with it but it might have helped on the journey I had on Saturday
when it took more than an hour to drive 2 miles to Tesco.
My first car had an automated choke that was supposedly operated by flooring the accelerator, it usually didn't work and I'd have to flood
the carb to get it going.
In a White Room, With Black Curtains, By the Station.
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coyoteboy
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| posted on 24/9/14 at 10:17 PM |
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Just ran the numbers but phone lost the whole lot. Yes it's worth it by miles both in fuel terms and even if you have to replace a starter and
batt every 5 years.
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whitestu
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| posted on 25/9/14 at 07:44 AM |
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The only experience I have of them is on a Prius which is a bit different. That worked really well and it was actually quite difficult to tell whether
the engine was running or not if you had the radio on.
The engine seemed to start instantly when the throttle was pressed. It maked a big difference to MPG compared to the Passat tdi I had previously. Both
would do the bets part of 50 mpg on the motorway but the Passat would drop to as little as 25 in central London whereas the Prius still did around 50.
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