Lately, I have seen a lot of drivers turn their car engine off at traffic lights to save fuel, and then restart again when it is green light.
Is this an OzBargain way to save fuel ??
Turning the car engine off at traffic lights
punter1 on 16/03/2014 - 17:12
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I have seen older cars too, not the hybrid ones.
Mazda Skyactiv Technology with idle stop feature stops the engine when you're at a complete stop with adequate pressure applied to brake. If it's a hot day and the AC is on the car won't stay turned off for long but if you don't have your air con or heater running it'll stay off for about up to 5 mins in my experience
Yeah my merc does it too - gets annoying on hot days as the AC shuts off along with the engine, although the fan keeps running.
Often I think geez this AC system really sucks - can't keep up with the heat - then I realise oh wait..
Skyactiv
Who thinks of these names?Haha… yeah what does sky and active have to do with efficiency??
Or what about BlueEffiency! Why is blue the colour of efficiency?My Bugatti Veyron has this option too. I don't usually activate it
Current Subarus do it too. Kind of annoying if you're not expecting it. The real downside is that the aircon stops as well.
Blue is the colour of efficiency, red is the colour of hunger (KFC, McDonalds, Red Rooster, et al) and purple is the colour of sexual tension. Everyone knows that :P
It does not happen on smarter cars ;)
then barney the dino should be in jail…
It starts up when you let go of the brake pedal.
I have couple of my neighbours who leaves home around the same time I leave and if they manage to get on the street first I have no choice but crawl behind them at very slow 5-10km/h and stop for few minutes at every single turn as they wait for the whole street to be completely empty to turn. It drives my frustration this way until I hit the main road. Then get to the main road signal light and they take long time to start moving after light becomes green which almost not allow anyone else to cross the light after them.
Those who are very slow responders at green lights during rush hours should be named as SkyActive drivers.
You should make a short film about this, it'd be hilarious.
I have driven one of those automatic ones a few times (BMW 1 & 3 series). It feels weird stopping at the traffic light…everything stopped, car gone all quiet… as if it stalled. It became really annoying when driving in the traffic jam, stopping and starting all the time. Not sure how fuel efficient it was, but it was so annoying that I had to disable that on-off function.
It should definitely save fuel when the engine is idle for long enough and it keeps the engine turned off for that duration. However I am not sure how it can save money because it affects the running temperature of the engine. When the engine is below optimum temperature it takes more fuel to run and that's bit significant difference. If stopping of the engine happens too frequently, drop of the engine heat might negate any saving we can get by turning the engine off (unless those skyactive engines have some feature to retain the heat in engine for longer that normal engines) plus any extra cost on the wear of the starter motor and affect on the battery.
An engine switched off will not cool fast enough to induce 'cold start' fuel delivery, or any fraction of that.
Cold start runs for the first few minutes of starting up a vehicle until it reaches a threshold temperature, of (just taking a guess) something like 50 degrees C, to stop the car from stalling (as you would with a choke on an old carburetor car).
At a guess, to initiate cold start, you would have to have the engine off for at least an hour or two, but probably more. And of course, depending on the outside ambient temperature.
From what I have heard, the effect of stop-start on fuel consumption is marginal. It is more used by manufacturers to reach the required numbers on CO2 emission so they can pass regulatory requirements (Euro V, Euro VI etc).
The start-stop systems are pretty cool. The engine restarts as soon as you take the foot off the brake pedal. Takes a bit to get used to.
I wonder what the battery drain is like, if you have say car wipers and air-cond on with the engine off, all the power would have to come from the battery.
Yeah I find my car will only auto-shut off if there's sufficient reserve in the battery. Sometimes mine won't auto-shut off if I've just started the car and haven't been driving for long.
Also, the fans keep running but the AC is turned off. Not very pleasant on a hot summer's day.
Air conditioning stops when the engine stops.
Not always. My Civic Hybrid stopped automatically at the lights and with this in mind the AC was driven by an electric compressor that kept running. Past tense because last week someone drove into the back of me and wrote it off :-(
I always turn off my car if I know I will be stopped for more than 1 minute. Not sure how much (if any) fuel it actually saves..
Amateur. The REAL masters of the road turn off the car, get out and go to the boot and rat around in their shopping bags for a snack.
Not worth it for big engines.
If you know you're going to be stopped at the lights for a decent amount of time it could be worth it. Otherwise the wear on the components isn't worth it.
Just leave it on, the petrol usage is minimal while idling."Just leave it on, the petrol usage is minimal while idling."
I don't believe it; especially in an automatic.
I think shifting into neutral reduces the load on an automatic and can lessen fuel consumption.
In fact many newer automatic cars change to neutral when stopped and the brake is applied. They shift back into drive when the brake is released.
I wouldn't try doing this in older cats though, seems a good way to reduce engine/starter motor life.
Yes. Older CATS are much grumpier.
Yep you will kill your battery and starter motor in no time driving like this in a car that does not have stop start technology, they are not designed to take it. Full stop end of story.
(Source - My brother is an Auto Elec and people doing this are keeping him in business, so keep it on the down low lol !)Even poorly designed or 'first model' of vehicle with this tech are failing earlier than they should.
Some people are requesting that the stop/start be overridden in their vehicles so that the starter and battery last longer, even though they are actually designed to take the punishment (also costing a boot load more to replace than normal batts and starters).
It's pretty minimal. On my friend's golf it uses 0.5L/hr while idling. 0.9L/hr with the aircon on.
I think NRMA suggests around 45 seconds is the average time needed to be stopped to get a benefit.
Link?
It might be good if the car is designed for it, but I wouldn't do it manually. I expect the wear and tear on the engine would outweigh any fuel saving.
A taxi driver would never turn their engine off. They run all day, and get 100s of 1000s of kms out of their engines.Taxi drivers usually turn of their engine if they think they'll be standing for more than a few minutes, e.g. at a long rank during a quiet time of day. It's rarely long enough for the engine to get cold though, which is why they last so long.
Not a good example.
If they don't own the car and are just a driver, they only have to pay for the fuel. Maintenance costs are the owners responsibility. If you're replacing your starter motor every few years it would easily outweigh any fuel saving you've made,
I've had several turn theirs off at intersections the first time it happened I was coming home from a party and I was pretty much like wtf?? I thought he broke down or something….
I agree with you on wear and tear, not worth it. Might not even save any fuel.
Yeh taxi drivers are constantly turning them off. Watch them sitting in a passenger pickup taxi zone queue in the city. One moves on for a pickup, the rest start up, drive five metres then switch off.
thing is taxi drivers dont own the cars
taxi is s $5,000 piece of crap Falcon
the license is $400,000
the car is effectively disposable
Falcon taxis cost far more than $5k, try more like about 30k.
None of them are brand new. They are usually all 5-10yrs old from auction houses, between $4K and $8K.
taxis are bought new and then sold 5-10 years later. let me know where i can get a 5-10 year old prius v for between $4k and $8k
Lol, not all taxi is a $5000 piece of crap Falcon.
I saw a yellow cab Aston Martin in Melbourne CBD the other day…. haha was about the pull out my phone but it ran away before I could get a pic.
I wonder what the 'super cool luxe car brand' premium fare is on that one..
I once had an accident that damaged the radiator and the vehicle kept overheating when idling.
So I started turning the engine off at lights, as a consequence I noticed I was able to get another 50-80km out of the tank :)
some newer cars inject more fuel when it reaches a certain temp to try and cool it down.
So the additional klms your seeing might not be 100% correct when comparing to a normal operating car.
if your getting 10% additional klms from a tank from doing this, you have problems with your car, your odo is out or you sit in traffic 90% of the time
most people will be lucky to get 10-15 klms extra from doing this.
Which new cars inject more fuel to cool it down mate?
Never heard of that hahaFollowing from that logic:
"To extinguish fire, aim petrol pump at the base of flame and squeeze trigger."
Which new cars inject more fuel to cool it down mate?
i know for a fact that the falcons do (or at least did a few years back). its called limp mode where they go fully rich if theres an overheating problem. they also used to shut down alternating cylinders for the same reason.
Following from that logic: "To extinguish fire, aim petrol pump at the base of flame and squeeze trigger."
this is the problem with internet experts…. go do some research on engine tuning and specifically air/fuel ratios and running lean (less fuel) makes a motor run hotter but makes more power and running rich (more fuel) cools them down but less power. this is also why you see in racing cars when they go into deceleration (foot off the accelerator) they shoot flames out the exhaust. its called "rich on overrun" and its to cool the internals of the motor (pistons/heads).
More fuel being injected doesn't mean bigger bang/fire etc.
The additional fuel is not a complete burn, so the combustion is actually cooler which means less heat in the head, piston, bores and exhaust manifold.
in the case of most cars, there is only so much air that can be pumped in, and only so much needed for optimum burn, any more then that is generally wasted and not burnt properly
The majority of cars from 1990 will have this, its a pretty basic compensation.
This is pretty general, I could explain in detail, but if your interested just google it
That's a horrid example and detracts completely from your point. If there is a small fire, dousing it with petrol would actually work. Petrol in liquid form isn't flammable, only the fumes are.
you'd need to be idling for 5 hours to save 5 litres to go another 50km.
I have a Touareg VW that has the what they call blueMotion a start stop system it can be overridden when you are in heavy traffic. I don't think it saves much if any in mileage but I think its supposed to be better for the environment with less emissions. In Europe where they get taxed on vehicle emissions it puts the car in a lower category and so saves them on a car emission tax.
You get used to it and works well the down side though is when you have friends in the car and they wonder why you keep stalling.
+++1 to Touareg :)
You shouldn't turn off your car engine at traffic lights unless your vehicle is designed for it. I've already put it into real world practice for about 3 weeks on my normal car. I knew the timing of the traffic lights and when I'd be sitting idle for longer than 30 seconds. I was smug knowing I was saving petrol not idling needlessly. In the 3rd week of smugness one morning I went to start the car - flat battery. When I thought about it what I was doing was adding more wear and tear to the ignition also.
I read a study that a transport company did this for their trucks/vans and saved around 5-10% of fuel costs.
Thanking for testing it out and for letting us know the result. I guess myth busted
The starter motor draws +100 amps (somewhere I even read over 300 amps) to start the engine. Doing this frequently in heavy traffic will not give the battery sufficient time to recharge back up to normal levels.
Exactly, however I hadn't thought about it at the time until I had a flat battery. Luckily my car is manual so I made sure there was water in the battery cells, roll started it and went on a 40 minute cruise to recharge. All sweet after that.
In the 3rd week of smugness one morning I went to start the car - flat battery.
yup you found out the hard way that batteries dont like cranking engines over and that batteries take a long time to recharge.
i cant help but wonder if these wanky "active" cars have some sort of capacitor setup for cranking like that rather than relying on the battery which was never really designed for that sort of load.
also by your battery going fully flat like that you have probably just killed 1/2 of its capacity. lead acid batteries hate going dead flat and it kills them very quickly.
Yes, something called an i-ELoop series of capacitors (I read that as Eneloop… too much Ozbargain =/)
And it is for the purpose of reducing emissions, not sure if it actually saves fuel:
http://www.autocar.co.uk/car-news/new-cars/mazda-6-gets-adva…
oh now there is some good info.
seems that while braking it cranks up the alternator to charge up a bank of capacitors so it does not have to use extra fuel when it restarts to recharge the battery.
so yea, simply turning off your motor at the lights is a bad thing and in no way a comparison to cars specially designed to do it…. :)
How about putting the car in neutral?
Difficult in a automatic, but yes used to always put the car in neutral and coast downhill in my manual gearbox car.
How about putting the car in neutral?
this should use slightly less fuel for little negative effect (tho im no auto trans expert, all my knowledge has been with manual cars)
used to always put the car in neutral and coast downhill in my manual gearbox car.
if your cars fuel injected DO NOT do this. you are wasting fuel. with an EFI car over a certain revs (usually around 2000rpm) with the throttle closed the ecu actually turns the fuel injectors off completely. if you put it in neutral and coast down idling your engines still using fuel.
i your cars an old carby car then you can do this as long as you bump start it before you stop (not starting it with hte key)
Hi Nosdan. With automatic transmission, does placing the transmission into neutral disengage any sort of radiator circulatory system, or lubrication? It was my understanding this is one of the reasons why it is bad to coast in a vehicle with an automatic transmission because the engine or transmission would start to overheat.
like i said just above, im not any sort of auto trans expert tho i do understand them probably a fair bit better than the average.
from what i understand, generally, with the trans in neutral you stop the trans fluid pumping though the gearbox, this is why its bad. this can stop fluid from getting to the parts that need lubrication when moving which is probably what causes the trans to heat up.
as for the "radiator circulatory system" on most auto cars they pump the trans fluid through your radiator (in its own separate sealed system) to use your radiator water to keep the trans fluid at its optimal temp (warm it quickly when its cold and stop it getting to hot when it heats up). obviously if your trans fluid isnt pumping the fluid around it cant use this system to keep the temps in check.
lastly, its also not good to do anyway because of the reason i outlined above, when your cars in drive and moving along with your foot fully off the accelerator it will shut down the injectors anyway so using zero fuel. putting it in neutral while coasting means you hav to use fuel to keep the motor idling.
This is not entirely correct, The automatic transmission is pumping oil continuously however probably at different rates.
This is why you typically have to check the fluid level when the engine is running in park.If you think about it, It would be quite silly only pump oil when the car is in gear. This is because the drive shaft into the transmission is continuously turning when the engine running, this would pretty much destroy the main bearings in the transmission due to lack of lubrication.
I know that the Landrover Freelander Td4 owners book actually recommends you put it in neutral at a stop to save fuel. Whether other manufacturers do is a another thing.
Putting the can in neutral while coasting or moving in my opinion is quite dangerous, and you may cook the clutch friction plates if it selects the incorrect gear for the speed.
It has no purpose like you said, the injectors shut off when decelerating. So if your coasting down a hill with the foot off the accelerator then you use no fuel."if your cars fuel injected DO NOT do this. you are wasting fuel. with an EFI car over a certain revs (usually around 2000rpm) with the throttle closed the ecu actually turns the fuel injectors off completely. if you put it in neutral and coast down idling your engines still using fuel."
I agree with your statement regarding the injectors turning off. However highlighting "DO NOT" implies this is a common, happens often and saves fuel. This is not the case. This does not happen often and the fuel saving are negligible.
On the various cars I have owned the hill would need to be a steep and I would have to change down a gear to get the revs up. Only then would the injectors would turn off and for only part of the trip down the hill as the gear change would slow the car down bringing the revs down as well.
I hazard to guess that the opposite is true. Coasting down a hill in neutral will use less fuel whereas the act changing down a gear to bring the revs up would use more overall.
U Mad?
If you're in NSW, how did you pass your learners test? This is an fail criteria in NSW:
http://www.rms.nsw.gov.au/licensing/downloads/guide_driving_…
page 30
- FAILING TO MAINTAIN PROPER CONTROL OF THE VEHICLE
This fail item applies to anything that could, or does, result in you losing
control of the vehicle such as:
• Clutch coasting (allowing the vehicle to roll along with your foot on the clutch) or coasting in neutral
U Mad?
dunno who your actually talking to, but ill give it a shot..
bingsta 20 hours 40 min ago
How about putting the car in neutral?given that this thread was about when stopped at the lights they would be tlaking about knocking it into neutral/park while at lights.
put the car in neutral and coast downhill in my manual gearbox car.
i have already explained why this is a bad idea.
as for passing my L's, when i did it decades ago there was plenty of stupid shit you were told not to do that any competent driver is more than able to achieve (changing down gears while slowing/braking was just one). unfortunately the tests are designed for dipshits who imo should never have had a licence in the first place. but this whole thread has nothing to do with legalities or even driving on open roads, this would apply to someone on a farm property or a racetrak equally as much as the roads. you shouldnt just assume…
many decades of racetrak driving and trophies/awards not to mention building race cars etc gives me a bit of a one up on the "average" road driver.. :)
@nosdan lol was talking to MMM, from the looks of things, you know far better than to coast in neutral =P
- FAILING TO MAINTAIN PROPER CONTROL OF THE VEHICLE
Using OBD data, a Diesel 4wd uses approximately 2L/Hr whilst idling. So idling for an hour would only use 2L. Maybe not much in terms of 150L large 4WD tank, but a much bigger % of say a 45L or less tank.
diesels are quite a bit different to petrol cars/motors. i also wouldnt trust obd data at such small injector dutys. it gets very hard to project real world use when your going down to such small percentage duty cycles.
in case you dont know, instant fuel usage stats are calculated by knowing what size the injectors are (cc/min) and using the injector duty cycle %. the problem with that at low duty is that it takes time for the injectors to open once the pulse is sent (this is injector dwell time) which can throw out the calculations a long way
What year?
What make?
what engine model?
One day when these 'new' cars get old, they will develop starting issues, I wonder what sort of wear it puts on the engine..
I believe they introduced the stop start technology to get better emissions ratings, not necessarily for fuel advantages.
Would be interested to see scientific reports in regards to engine/ignition wear and tear over the years compared to not having this feature.
The manufacturers don't care if they add more wear and tear as long as it lasts at least 3-5 years depending on their warranty, after that if anything breaks… they just earn more money by charging the customer.The manufacturers don't care if they add more wear and tear
i would go as far as saying they do care about wear and tear to the point that they spend millions on testing etc to ensure things only fail outside of warranty, then the more it fails the better. they hve been doing this for decades now.
Proven true from the Audi timing belt class action that happened a few years back in the US… Since it was interference design, when the timing belts kept snapping just outside of warranty, it caused catastrophic damage to the engine which = engine rebuild / replacement.
Same thing happened with Volkswagen. It was alleged that both companies knowingly concealed information regarding the failure from consumers and they ended up paying the repair bills for everyone affected.
http://www.pswlaw.com/Notable-Cases/Audi-and-Volkswagen-Timi…
wow people… way to totally fall into sales pitch BS while not understanding cars electrical systems.
when you turn your car off anything you have on (radio etc) runs off battery power. when you start the car it takes a huge chunk of power out of your battery also. the ecus also have to squirt extra fuel while cranking to get the motor to fire again unlike the lean conditions you get while idling with no load (load = aircon/alternator/thermofans/etc).
once you restart your car the battery needs to get recharged to replace that lost power. this takes extra fuel as well for the extra engine power needed to power the alternator.
you then have to go into the extra wear on all the starting components, starter/battery/relays/etc.
also have to take into account the effect on the motors internals. engine starting causes most of the engine wear over a cars life. this is why cars driven a lot of "country miles" are often in better shape than a car thats only done short trips to and from the local shops its whole life. each time you turn the motor off you lose oil pressure, it takes time to build that pressure back up and in that time all your internal clearances are wrong and poorly lubricated.
but lastly…. the tiny amount of fuel you save while the cars at operating temps at idle is minuscule. tiny fractions of a litre. this is a total off the top of my head guess, but its probably somewhere in the region of a litre per hour. turning it off for a couple of a minutes at lights each time just does not represent any real world savings.
if your going to be pulling up somewhere for 5-10 mins without any electricals on then sure turn the motor off, if your only thinkin about doing it at traffic stops dont waste your time.
oh, i also forgot about the o2 sensor trimming the fuel maps… for the o2 sensors to work correctly they need to be very hot. even rolling down a hill in gear is enough to cool them sufficiently to stop them working. when your o2 sensor is cold the car needs to run in a more rich fuel trim until it gets a reliable signal again. this will cost you even more fuel once you start your motor and drive away again (on top of all the other things i mentioned above using more fuel)
engine starting causes most of the engine wear over a cars life
you mean cold engine starting right? a cold engine start is what causes the most wear, i.e lack of oil and low temp, engines work most efficiently at their optimum operating temperature, also goes for transmissions, some cars with automatic transmission won't shift into higher gears such as over drive until the transmission reaches a certain oil temp like 60 degrees
cold starting is the worst sure. tolerances between hot/cold expansion for steel (blocks/sleeves/cranks/cams/etc) versus aluminium (pistons/blocks/heads/etc) is a lot different. when engines are built they are built to hot tolerances because most of its use will be when its hot. add to that the fact when you first start you have cold thick oil that needs to build up pressure to get to where its needed and temp etc. you also tend to lose oil from the bores/bearings etc when the motors stopped so the first few(?) rotations of the crank there is insufficient oil between the bearings and the crank etc
but all starting is bad for a motor. seconds after the engine stops you have lost all oil pressure. this means less lubrication till the pressures built up again.
obviously both of these are only slight wear each time, minuscule (probably) unmeasurable amounts, but if your doing it 50 times a trip over the years its going to add up.
this is part of the reason you regularly see taxis have done a million km's on the original motor. motors always running, always warm, always lubricated = virtually no wear.
Engine wear is only a problem with cold starts, a min or two rest wouldn't be the same thing. As others have pointed out taxi's don't leave their engines running if they can see they're going to be stopped awhile. The secret for long engine life is not keeping it running, but avoiding cold starts.
Absolutely right, turning the key for ignition takes a huge chunk out of the battery, really not worth it.
can we ban this topic? and the neutral with an auto one as well
this sort of question belongs on yahoo answers
I actually read the whole thread. Very interesting. A lot of things can be found on Yahoo answers.. Doesn't mean they can't be discussed here.
I'm no car expert, but I always assumed it was common knowledge that the amount of fuel required to start an engine compared to letting it run in idle, would negate any fuel savings made by turning off the engine at a set of traffic lights.
….and the extra wear in tear on engine components will cost you more in the long run. DON'T DO IT !
Remember, cars with idle stop technology are designed to work that way with parts that have been tested under those conditions.
I always assumed it was common knowledge
unfortunately common sense isnt very common these days. people tend to be more gullible imo
Remember, cars with idle stop technology are designed to work that way with parts that have been tested under those conditions.
any source to this or just an assumption on your part? i would imagine that the couple of years warranty you get on new cars would have ended before you see any real issues and of the rest (batteries etc) would fall into fair wear and tare so not covered under warranty past the first few months/year.
Yes, source is Me, I am a design engineer for a major auto company, with 20 years experience.
Germans have been doing this for decades
Yes they do this in Germany and Switzerland and their cars are designed to stop the engine automatically and start automatically when you want to drive again.
With town traffic lights, it's not worth switching off but with stop-go boards when you know they stop you for 2 mins plus, I always switch off and take the stress off the clutch spring by going into neutral and applying the handbrake. Then you can chill until you can see the end of the traffic coming through the roadworks. I worked in Europe for 5-6 years prior to 2010 and was surprised at how relaxed they were towards driving. Here it's all nervous energy, tailgating and impatience over someone doing 95 in a 100 zone and that sort of crap - It's a 100 speed limit not zone because you can't go over it can ya!
Exactly and if you back off 20m (more accurately, have a 2 second gap) you and your passengers are much more relaxed and, Oh Darn, I arrived 2 seconds later that I would have.
Wouldnt it use more fuel having to start the car up again rather than just letting it run idle. Sounds more expensive to me
my Golf idles at 1L/hr, so saving $1.70 an hour. less the additional fuel required to start the engine.
see the 2nd part of https://www.ozbargain.com.au/node/136930#comment-1888125
as well as https://www.ozbargain.com.au/node/136930#comment-1888945
i wouldnt put to much weight on the idle usage numbers being very accurate… but your point is valid that even in a best world situation your really saving next to nothing even before you begin to take in all the rest of the problems with doing it
it's clear most here agree that switching off the engine when stopped for brief periods has little if any benefits, personally i think something like the Chrysler's 300C V8 engine that can switch off 4 of the 8 cylinders is the way to go for saving fuel under low load/idle conditions, i wonder why it isn't used in more cars
imo this is just another marketing stunt. switching off a cylinder does not remove it from the engine. all the same frictions are still there. there is quite a lot of friction between the rings and bores etc amongst other things. switching off a cylinder simply means you have to use more fuel in another cylinder to catch up again and it also makes the engine less balanced again robbing more power. if this "technology" actually had any practical use it would be used in top level car racing but it isnt. all they do is lean the mixtures out which gives the best efficiency…. which is exactly what road cars do anyway.
I recall reading a study (haven't got link) that if a car is stationary for around 30 seconds or more it's worth switching the engine off. The extra fuel required to start the vehicle will be less than the fuel burned during 30 or more seconds.
But you have to consider the wear and tear on the starter motor and battery to determine whether it's worth it. Hybrid and start/stop cars are specially designed while your average vehicle just isn't designed for frequent engine cycling. Lead acid battery life is likely to be shorter if you frequently switch the engine off at the lights. My Exide SLA battery has a 3 year warranty for private use, 1 year for business and just 6 months for taxi use. Sure, taxis cover many kilometres within that year but the much shorter warranty is also due to the frequent switch off/on that drivers of conventional LPG vehicles do while waiting and crawling through the taxi queue.
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This actually a built in feature in newer cars. My mums car does it automatically. The car turns the engine off and automatically starts up again when you accelerate.