The usefulness of a start-stop system should be looked at critically. After driving for a good two years with such a system, one is sometimes inclined to be doubtful. As far as the theory is concerned, the benefits are obvious. When waiting for the lights to change to green, the engine switches itself off. Indeed, how long is the light going to stay red?
And what if one isn't the first car in the line?, sometimes the driver ahead of you creeps slowly forward before finally stopping. Isn't it ridiculous, to rush up to the traffic lights so that the start-stop system can be more efficiently used?
In everyday driving, I often leave the car in gear and keep the clutch pedal pressed, to prevent the engine from switching off. I know how long the lights take to change and I know that in a few seconds we can drive off again. In this case, the switching off is pointless. At least this is not completely senseless. Who knows, how much earlier the starter will give up it's ghost.
The interesting question is of course, why the manufacturers push this system. Thereby, one should be aware that the currently valid NEDC-test to determin the consumption, shows an above average number of stopping points. In addition, the pauses are also fixed.
A comparatively reasonable system is exactly what they need, whereby the individual- or also the package-systems are partly offered as an optional extra which one has to pay more. Added to this, the same calculation as is used for hybrids is valid, this means that the fully charged battery is not taken into account.
Because the manufacturer doesn't have to include the energy that is needed to start the engine, every running-pause benefits the CO2 value or the fuel consumption. Unfortunately, this test-method has as little to do with reality, as little in fact, as the whole NEDC-test itself.
Let's take a tailback on the motorway as an example, when, I ask you, does the car stand still for long enough that the start-stop process is worthwhile? In the past, if the delay was long enough, we switched the engine by simply turning the ignition key. The question of whether the clutch suffers when it is permanently pressed, remains unanswered. In the past we never did it that way.
Of course the more intelligent solution is lurking in the background, it is however, more complex. This would be not only the actual pulling off, but also the possibility of pulling off using electric power. In addition, it should be possible to drive the car without using the engine ('coasting'), whereby the engine should then very quickly start as to be used as an engine brake. 06/13