Do 'stop start' cars save money?

Ditzy_Mitzy

Stopping and starting makes me feel better because it has rendered all sorts of expensive, flash cars slower off the line than my old heap.  I have noticed, however, that drivers round my way seem to do something to trick the system into restarting the engine as soon as it stops; I seem to recall that depressing the clutch does that, but haven't driven a stop/start car for years.  

As for saving money, who knows?  A four cylinder engine will consume somewhere between a tenth and two thirds - capacity and fuel type dependent - of a gallon an hour at idle.  How long do you spend at idle per journey with the engine warm?  Specifically at idle, not crawling in traffic.  An urban motorist might idle his engine for ten minutes, possibly more.  A suburban driver perhaps only idles for a minute or two.  If the latter has a relatively efficient car, perhaps a half gallon an hour idler, it might take three months to get through a gallon of fuel at idle.  

Like most hybrid* systems, stop/start probably saves a bit of money in the right circumstances but is not a panacea.  In London it will have a moderate effect; in rural Scotland it will be completely pointless.  

*I remain dubious about petrol-electric hybrids and genuine fuel savings as the things seem to foster a poor driving style.  The combination of powerful brakes and the torque boost from the electric motor seems - as has been my experience in taxis - to encourage heavy braking and harsh acceleration.  

Teapot55

Ditzy_Mitzy said:

Stopping and starting makes me feel better because it has rendered all sorts of expensive, flash cars slower off the line than my old heap.  I have noticed, however, that drivers round my way seem to do something to trick the system into restarting the engine as soon as it stops; I seem to recall that depressing the clutch does that, but haven't driven a stop/start car for years.  

As for saving money, who knows?  A four cylinder engine will consume somewhere between a tenth and two thirds - capacity and fuel type dependent - of a gallon an hour at idle.  How long do you spend at idle per journey with the engine warm?  Specifically at idle, not crawling in traffic.  An urban motorist might idle his engine for ten minutes, possibly more.  A suburban driver perhaps only idles for a minute or two.  If the latter has a relatively efficient car, perhaps a half gallon an hour idler, it might take three months to get through a gallon of fuel at idle.  

Like most hybrid* systems, stop/start probably saves a bit of money in the right circumstances but is not a panacea.  In London it will have a moderate effect; in rural Scotland it will be completely pointless.  

*I remain dubious about petrol-electric hybrids and genuine fuel savings as the things seem to foster a poor driving style.  The combination of powerful brakes and the torque boost from the electric motor seems - as has been my experience in taxis - to encourage heavy braking and harsh acceleration.  

Frequent heavy acceleration and subsequent heavy braking surely cannot be economical, yet practically every motorist where I live seems to prefer this style of driving. The only exceptions are bus drivers and so-called ‘doddery’ old people. Oh, and hearse drivers.  

molerat

Past 2 cars have had it and I don't find it a problem.  The only time it kicks in is when stationary, in neutral and foot off clutch.  Surely if you are at a junction easing out none of those would apply. When stopped at a junction by the time the car is in gear the engine is running.

Alanp

Stop start was introduced to meet manufacturers emissions targets, some systems work by dipping the clutch and the engine starts, I have just px,ed my mild hybrid puma, the ss worked as soon as you engaged first gear, and would allow you to coast with the engine off at less than 10mph, which ,I suspect, most mhev work this way, ( I could be wrong) the starter motors fitted to ss enabled cars are able to deal with the constant stop and starting, whether they save fuel will depend on how long you are stationary, of course it also depends on other factors as to if the system activates, low temperature, cold engine or high use of the aircon all play a part as to whether it engages or not…

onomatopoeia99

sevenhills said:

Rodders53 said:

I thought that stop-start was all about emissions reduction when vehicles are stationary, rather than fuel savings or economy?

But I believe that every time you start your engine, more fuel is pumped in, in order to start it.

No.  When you start an engine that is cold it uses more fuel as the mixture needs to be richer, but once warm it starts at the normal mixture.

If you think about it, a carburettor made by Skinners Union (e.g. the HS2 and HS4 types used by BL in the 60s and 70s) on an old car has no electronics and the fuel is drawn in by the suck of the airflow as the starter is cranked, it doesn't magically know you are starting the car so pump in loads of extra fuel (which would flood the engine and prevent it firing anyway)

daivid

Ditzy_Mitzy said:

  I have noticed, however, that drivers round my way seem to do something to trick the system into restarting the engine as soon as it stops; I seem to recall that depressing the clutch does that, but haven't driven a stop/start car for years.  
  

Works on mine; the engine stops when the handbrake is applied and gear in neutral and clutch pedal is fully up. I'm quite happy with the stop/start system, waiting at a junction/obstruction I keep the clutch down so engine running and ready to go, at a red light I let it engage unless sure green is imminent. How much fuel is it saving me? No idea, the majority of times my stop/start engages I would have switched the engine off in the previous car. On the other hand the number of people I see running their engines when they know they are going nowhere for several minutes I think the roll out is a good thing.

ontheroad1970

sevenhills said:

WellKnownSid said:

If we didn't have progress we would all still be riding around in cars with these, and I remember the uproar and problems when car manufacturers first tried to remove them!

When AI knows how long you are going to be stationary, stop-start may work.

When I anticipate I am out to move off, I loosen my foot on the brake pedal in anticipation. Read the road and you can anticipate better.

Username03725

Some interesting responses, here, including those that see it as a gimmick or a con to beat fuel efficiency figures. 

It's not primarily a fuel saving economy device. That it does save fuel is a bonus but primarily it's there to reduce emissions, which is does quite well when applied to an ever larger proportion of the 30m+ vehicles on UK roads, and a lot more world wide. Waiting for lights to change or being stuck in a jam is the ideal time for it to kick in. 20 cars sitting for a 70 second traffic light cycle can generate a lot of emissions, and stopping the engine saves a good proportion of that. No brainer. It reduces fuel consumption figures on the urban cycle for the same reason. That's not a con, it reflects real world usage, but dismissing it as pointless misses the point that the whole standardised economy tests aren't close to real world usage but do provide a valid baseline comparison. It's also why it's active by default - installing an emissions & fuel-saving device that reduces consumption slightly but relies on the user actively choosing to use it? Hmmm...

Stop start kicks in only when the EMU allows it. Parameters are battery state, electrical load, engine temp, outside temperature, how long since last full start and last restart, and a few more no doubt. All that means it only kicks in if it's ok to kick in so the chances of being stranded when it fails to restart are remote. Later systems (for a few years now) stop the engine with the pistons at optimum restart position, which is why the restart is much quicker than your Ford Anglia ever was. Yes battery & starter motor are upgraded so are more expensive, but modern cars are full of things that weren't fitted in the past and make it more expensive - cat converter, DPF, air con, integrated infotainment systems, bigger wheels & tyres, electronic handbrakes, safety cells... Picking out one specific device as a costly extra misses the point of development over the years. Things change. And like the rest of your car's shedload of additional equipment, the older the car is the more chance there is of it failing. For those that run a car from years 0-3 they're ok - warranty, statistically unlikely to fail. Yrs 3-5 risk is increasing but still ok, and for those who buy cars older than 5 and those who plan to run them to end of life there's a high chance of expensive failure anyway, but there is across the board on lots of its equipment.

On my last few cars SS happens only when in neutral at zero mph with foot off the clutch. Anything that changes that simple equation restarts the engine, instantly. It doesn't cut out when rolling to a junction, or when about to move off. Maybe there are some that can be beaten but given the safety aspect of it kicking in when you most need power it'd be surprising if that happens any more than blue moon regularity.

motorguy

Username03725 said:

Some interesting responses, here, including those that see it as a gimmick or a con to beat fuel efficiency figures. 

It's not primarily a fuel saving economy device. That it does save fuel is a bonus but primarily it's there to reduce emissions, which is does quite well when applied to an ever larger proportion of the 30m+ vehicles on UK roads, and a lot more world wide. Waiting for lights to change or being stuck in a jam is the ideal time for it to kick in. 20 cars sitting for a 70 second traffic light cycle can generate a lot of emissions, and stopping the engine saves a good proportion of that. No brainer. It reduces fuel consumption figures on the urban cycle for the same reason. That's not a con, it reflects real world usage, but dismissing it as pointless misses the point that the whole standardised economy tests aren't close to real world usage but do provide a valid baseline comparison. It's also why it's active by default - installing an emissions & fuel-saving device that reduces consumption slightly but relies on the user actively choosing to use it? Hmmm...

Stop start kicks in only when the EMU allows it. Parameters are battery state, electrical load, engine temp, outside temperature, how long since last full start and last restart, and a few more no doubt. All that means it only kicks in if it's ok to kick in so the chances of being stranded when it fails to restart are remote. Later systems (for a few years now) stop the engine with the pistons at optimum restart position, which is why the restart is much quicker than your Ford Anglia ever was. Yes battery & starter motor are upgraded so are more expensive, but modern cars are full of things that weren't fitted in the past and make it more expensive - cat converter, DPF, air con, integrated infotainment systems, bigger wheels & tyres, electronic handbrakes, safety cells... Picking out one specific device as a costly extra misses the point of development over the years. Things change. And like the rest of your car's shedload of additional equipment, the older the car is the more chance there is of it failing. For those that run a car from years 0-3 they're ok - warranty, statistically unlikely to fail. Yrs 3-5 risk is increasing but still ok, and for those who buy cars older than 5 and those who plan to run them to end of life there's a high chance of expensive failure anyway, but there is across the board on lots of its equipment.

On my last few cars SS happens only when in neutral at zero mph with foot off the clutch. Anything that changes that simple equation restarts the engine, instantly. It doesn't cut out when rolling to a junction, or when about to move off. Maybe there are some that can be beaten but given the safety aspect of it kicking in when you most need power it'd be surprising if that happens any more than blue moon regularity.

Good summary.  

Herzlos

forgotmyname said:

Works better on some cars compared to others. Only helps if you do the type of journeys where it will switch
the engine off. Family members journey is short enough where the parameters are not met for the stop
start to kick in.

I took them to work one day and then took it to the MOT for them and it was a PITA, just about to pull out onto
a busy road with limited gaps and it cuts out. Luckily I was quick enough to abort pulling out.

The stop start system really should not have thought that was the correct time to cut the engine.

Stop start should only kick in when you're in neutral with your foot off the clutch, so I can't figure out why it'd turn the car off when you're just about to pull away from a junction unless you're doing something strange or it's broken.


Normally it'll have the engine back on before you're even close to taking off from a complete stop.

My last 2 cars have had it, and whilst initially I'd disable it there's really no point.
It only really kicks in in the kind of heavy traffic where you're not moving for a while. It'd seem like a nightmare if you're the sort of driver to roll forward 2ft every time you can instead of allowing a small gap to appear.
My last one tends to turn the engine back on after 45 seconds.