Turning Off at Lights & MPG

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In D, my C200K idles at about 600rpm.
Slip into P and the revs rise to about 800rpm.
I would hazard a guess and say that the fuel consumption difference between the two is so small as to be virtually unmeasurable outside a lab.
 
All these stop start owners will undoubtedly save a bit of money on fuel till that dual mass flywheel / clutch gives up the ghost prematurely and hits them with a big "wear and tear " bill. :dk:
 
In D, my C200K idles at about 600rpm.
Slip into P and the revs rise to about 800rpm.
I would hazard a guess and say that the fuel consumption difference between the two is so small as to be virtually unmeasurable outside a lab.

Yet you can see it on the rev counter?

Obviously, loading the engine up will consume fuel, you can see quite a temperature rise on my EGT gauge.
 
I heard once years and years ago (before Stop/Start was even thought of) that starting a car is the equivalent of 90 seconds of idling it. So 90 seconds to 2 mins seems about right, but thats probably more for the older cars.

It's meant to be about 15 seconds now, even less for a diesel engine.

Switching off at every opportunity definitely improves MPG, that's how a lot of economy driving awards are won.
 
My old BMW 530 v8 could tell you how much fuel was being used in litres per hour if you pressed the right buttons on the computer.

Idle was at best 1.2 and 2.2 with aircon, lights, HRW etc.

20 to 37cc of fuel per minute.
 
Interestingly I was in traffic the other day with the van windows down. The wee black eurobox next to me (no idea what it was, they all look the same) had stop start. What a pain in the **** in the "inching towards the lights every so often" situation we were in.
Left me thinking about how many starter motors, ring gear, solenoids etc etc it would go through in it;s life. The manufacturing environmental and logistical costs surely would outweigh the environmental benefits of it being switched constantly on and off in traffic?

Find me a tree, I need a hug lololol
 
I believe that back in the days of carbs it would take more fuel to restart the car - particularly if you used part throttle, or blipped it when starting. With fuel injection there's none of that, so the "break-even" time for turning off is much shorter.

With an auto in "D", it's not just the difference in revs, it's the power the engine needs to produce in order to overcome the resistance of the box. Even if the revs were the same, it would use more fuel in D than P. Additionally, and as another example, electrical loads do the same. If you're sat in "P" even and turn the heated rear windscreen on, you'll hear the revs dip for a moment. This is due to the additional load on the engine causing the revs to drop, then the engine management increasing the fuel flow to maintain at the original level. It does the same when you sit in D - increasing the fuel flow to maintain tickover.

Cheers,
MarkP
 
If stopped for over 2mins its best to turn the engine off to save fuel, any less time, false exercise.

On my w202 c180 if its switched of for about two minutes the engine is immobilised by the alarm system which then requires it to be locked and unlocked before you can start the engine and then it might not start without setting the alarm off therefore you have to go through the process again,

so turning the engine off at the lights, no chance
 
I am not doing my bit and giving up curry....

Looks like we are not spared the x1 :rolleyes:




Sorry Steve, but that is my only experience of stop/start technology and have to say it is pretty impressive for saving fuel.
 
wonder if starting/ stopping increases wear and tear on starter motor etc?
 
wonder if starting/ stopping increases wear and tear on starter motor etc?

Of course it does, but manufacturers use higher rated components to combat wear.

Citroen were trialling a charge-alto system that replaced the flywheel, so no starter motor at all and very rapid starting.
 
If stopped for over 2mins its best to turn the engine off to save fuel, any less time, false exercise.

Some say 30 second, but both figures are probably pretty arbitrary anyway. ;)

But keep in mind the extra load on the starter motor and battery - Start-Stop technology may be kinder to the environment, but not necessarily to your pocket. :eek:

At any rate I wouldn't try this on short trips on a rainy night - with the lights, wipers, rear screen demister, and heating, all switched on, the last thing the battery needs is 2 minutes of heavy load followed by the starter motor - repeatedly... :doh:

Another interesting point is that in many places in Europe they have timers on traffic lights showing you how long before the lights change. This does not exist in the UK (not in London anyway), so when you are stopped at the lights there is no telling how long you will be... :confused:

So my view is that Start-Stop technology - or manual implementation of this principal - is plain bonkers.... :D
 
Some say 30 second, but both figures are probably pretty arbitrary anyway. ;)

But keep in mind the extra load on the starter motor and battery - Start-Stop technology may be kinder to the environment, but not necessarily to your pocket. :eek:

At any rate I wouldn't try this on short trips on a rainy night - with the lights, wipers, rear screen demister, and heating, all switched on, the last thing the battery needs is 2 minutes of heavy load followed by the starter motor - repeatedly... :doh:

Another interesting point is that in many places in Europe they have timers on traffic lights showing you how long before the lights change. This does not exist in the UK (not in London anyway), so when you are stopped at the lights there is no telling how long you will be... :confused:

So my view is that Start-Stop technology - or manual implementation of this principal - is plain bonkers.... :D


That was what I was trying to say earlier, but mentioned the X1 which upsets Steve, oops done it again! :p


The stop/start tech monitors the car, so engine temperature, battery load etc. etc. It will only work while all this is optimum.

Plus you don't really notice it anyway, as soon as you dab the clutch the engine starts and you're off, however, a timer on the lights would be nice as I always seem to get doddery git in front of me who looks to wait for the car in front to pull away before putting his car in gear, checking all his mirrors and then releasing his hand brake giving him just enough time to pull forward a car length just in time for the lights to turn red again!! :wallbash:
 
I recollect reading research on stop start and the time at which you save was much lower than anytimes posted here - it was 6 seconds.
My Mini diesel has stop start and I use it all the time in London traffic. Stop start vehicles have uprated components to take account of this feature. I find it useful and easy to use.
 
At say a litre an hour of juice used at tick-over and juice at £1.30 a litre it comes to a whole 2p a minute saving to your pocket.

I'll not bother.
 
Depends on where you drive.

If you are all town work it is a briliant idea.

Someone in London was moaning he was getting he was only getting 34mpg from his 118d, but then he was averaging 21mph and his tank at 450 miles took 20 hours to of driving to do as well.

20 hours is 1150 minutes, I would guess that 2/3 of that was sat in traffic.

The engine off would make a massive difference in that enviroment, those with the facelift model with stop start were getting nearly 50mpg as a comparison.

But if you spend most of your time moving and only have the occasional sitting at lights etc. then it will make very little difference. Someone who does 450 miles with an average speed of 40-50 and does it in 6 hours will not see the same benefit.
 
Has anyone really tested this?

I mean engine off for a couple of minutes is not going to make a difference in the scheme of things, except for cleaner air. I wonder how much you would use if the car was left to idle for an hour. No load, no turbos etc...a litre or less ?

Who has the time to try it?

DEL 320 posted on this subject a while ago , after accidentally leaving his car running outside his house and forgetting about it for a couple of hours , it had used surprisingly little fuel !
 
Im just curious as to how the new MB automatics are using the stop/start function? Do you put it in 'P' while at the lights??
Anyone know..
 
Im just curious as to how the new MB automatics are using the stop/start function? Do you put it in 'P' while at the lights??
Anyone know..

When I test drove a W204 recently, the engine shut down while still in 'D' - and restarted in 'D' as well. Eerily quiet when stopped at traffic lights.
 

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