Do 'stop start' cars save money?

Username03725

Robbo66 said:

Stop start is a con to get a lower emissions score, whether it actually does reduce emissions is anyones guess. Mine spend more time not working than actually working.

Not sure how it's a con. How can it not reduce emissions if the engine is switched off when you're sat at traffic lights? You can't reduce emissions to less than a non-running engine.

sevenhills

Username03725 said:

Robbo66 said:

Stop start is a con to get a lower emissions score, whether it actually does reduce emissions is anyones guess. Mine spend more time not working than actually working.

Not sure how it's a con. How can it not reduce emissions if the engine is switched off when you're sat at traffic lights? You can't reduce emissions to less than a non-running engine.

Quite a number of posters have stated that it does not do that, on many occasions.

Would it save money, CO2 and be legal to switch off with the key?

WellKnownSid

sevenhills said:

Quite a number of posters have stated that it does not do that, on many occasions.

Would it save money, CO2 and be legal to switch off with the key?

Leave it to the PCM to make that decision, far less chance of finding yourself without brake servo vacuum and sliding into the car in front or behind

Herzlos

sevenhills said:

Username03725 said:

Robbo66 said:

Stop start is a con to get a lower emissions score, whether it actually does reduce emissions is anyones guess. Mine spend more time not working than actually working.

Not sure how it's a con. How can it not reduce emissions if the engine is switched off when you're sat at traffic lights? You can't reduce emissions to less than a non-running engine.

Quite a number of posters have stated that it does not do that, on many occasions.

Would it save money, CO2 and be legal to switch off with the key?

Sure, if the engine doesn't turn off for whatever reason you're not saving anything. Any time it turns off for more than about 8* seconds, you're saving fuel.

Turning the car off via the key is likely a bad idea for a few reasons:
There's an argument about not being in proper control of the car, even if you're at a complete stop. 
It'll take you longer to start the car back up than if you let the stop/start do it.
It'll potentially turn off other stuff like the AC or radio which would be a nuisance.
You're not able to monitor the battery and engine conditions as well as the computer.


*8 seconds is the commonly accepted amount of time a car needs to run to save the fuel taken to restart it. It's probably based on some research at some point but it's probably no longer valid and will vary wildly from car to car. The average cycle time for a set of traffic lights seems to be somewhere from 60 to 90 seconds, which will result in plenty of fuel saved (and fumes not produced).

Goudy

It's reckoned stop start can save between 5 and 12% on fuel and emissions but it depends on the car, how it's driven and the system it uses.

Some systems are quite basic, just a battery monitor and a bit of programming that decides if it's safe enough to stop and perform a reliable restart.

Others are a bit more advanced that take into consideration things like climate control settings.

Others are almost hybrid like, they recover waste energy from slowing down and utilise that via a beefed up starter/generator to recover the energy and also restart the engine, but these systems are more expensive.

The first couple aren't really free, the engine is going to have to put that energy back into the battery via the alternator which means the engine is under more load and using more fuel to do that. 

Now if you think of a lot of short trips through a city, the stop start system will probably work a few times before the programming detects there is too much going out of the battery than coming back in and it's safer to disable the system until it this power drain reverses, but still you have had X amount of minutes with the engine off, not burning fuel/producing emissions that you otherwise would have.

Now this type of trip will use more fuel/produce more emission anyway because of all the accelerating and braking, so the few minutes it does stop has a great effect percentage wise.
 

 

Username03725

sevenhills said:

Username03725 said:

Robbo66 said:

Stop start is a con to get a lower emissions score, whether it actually does reduce emissions is anyones guess. Mine spend more time not working than actually working.

Not sure how it's a con. How can it not reduce emissions if the engine is switched off when you're sat at traffic lights? You can't reduce emissions to less than a non-running engine.

Quite a number of posters have stated that it does not do that, on many occasions.

Would it save money, CO2 and be legal to switch off with the key?

Some people have expressed an opinion that doesn't hold up, or have fixated on it reducing costs. Just because someone has written something on the internet it isn't necessarily true.

To repeat, it's not primarily about saving money, it's an emissions reducing device that works at scale. 20 cars held at traffic lights for 70 seconds will produce much lower emissions than the same 20 cars sitting there at tickover. Extrapolate that across towns & cities across the UK, then across Europe, then worldwide. How can that be dismissed as a con? A non-running engine produces fewer emissions that one that's running. That's unarguable.

Why would you switch off with the key when - as already been widely discussed - you have an inbuilt mechanism that does the same task more robustly, more securely, only does it when its conditions are met and stops the engine at its optimum restart position for minimum effort on restart? I'm not sure what mental process is going on here, that a tried tested integrated process can be replicated by 'switching off with the key'?

sevenhills

Username03725 said:

Some people have expressed an opinion that doesn't hold up, or have fixated on it reducing costs. Just because someone has written something on the internet it isn't necessarily true.

Why would you switch off with the key when - as already been widely discussed - you have an inbuilt mechanism that does the same task more robustly, more securely, only does it when its conditions are met and stops the engine at its optimum restart position for minimum effort on restart? I'm not sure what mental process is going on here, that a tried tested integrated process can be replicated by 'switching off with the key'?

I am very frugal, so saving money and being efficient is important to me, even if it's not my money.

But my SS doesn't work properly, so I switch it off. When I am not expecting it to switch off, it does, I pick up six passengers per day. Others in my line of work do the same, some just leave the engine running because they are wasteful and don't want a drained battery.

I personally rarely use aircon or even the blowers, our vehicles have had recharging issues, this could be why it does not switch off, if the battery is poor.

Herzlos

It sounds like there's something defective with it either the SS or the vehicle then, because you shouldn't need to care about it. The recharging issues could certainly be the problem.

When is it behaving like you don't expect?