Carsy

I drove a 250 CDI Coupe the other day & experienced Stop/Start Technology for the first time.I must say it was a weird experience for the engine to stop then start at the traffic lights.

Advertising say its advantage is that it is a fuel saver.

Thinking about it, I am having a problem with whether there are any savings in the overall scheme of things, ie Fuel savings Vs Cost of parts & maintenance.

Disadvantages I consider are :-

Extra wear on the battery, shortening its life or the vehicle needing a larger battery to maintain the extra load.( extra weight)

Extra fuel used to generate power to charge the battery . After all the load on the battery starting the car is high. Almost a dead short.

Extra wear on the starter motor & ring gear. In a city commute it may operate 30 times or more a day.The starter motor may not last the life of the car.

Worn starting parts may lead to less reliability.

Interested to hear any comments & first hand experience.

Is it a gimmick ?

JC

hyperion667

wow, excellent points to consider.....
this eco start stop stuff is so silly.....
subscribed!

robyc1982

can this start/stop system be disabled somehow?

acr2001

Good points. What happens when the A/C is on during a hot summer day? Does the engine stay on or blast you wit hot air?

dol4er

The ECO button turns off the Start/Stop. Also, the engine just won't stop and the climate control won't stop if it is hot in the car and you have set 18C, for example. However, if you have already reached the desired temperature, it will stop.

Diesel Benz

When you stopped at traffic lights and the engine stopped, did you hear the starter motor whirl when you pressed the gas pedal to go? No, at least if this is the same as on the W221 250 CDI, it starts with the alternator, no wear to the starter ring etc. as you assumed.

You can clearly see from the fuel consumption figures (city driving) how the feature reduces fuel consumption. If it didn't provide significant savings, MB engineers would not be that stupid to put that extra cost into the car.

Of course it still adds wear on some parts of the car (battery, alternator...), difficult to say if it helps more on some other parts (this is not the main design target anyway).

The engine starts with much less effort in this stop/start case because the engine is at operating temperature and most of all the electronics are fully aware of the engine timing (camshaft and crankshaft sensors signals are not lost unlike when the engine is switched off from the key). The engine needs very little power and fires absolutely immediately.

I need to check still if the starter approach is the same on a C-class as on the S-class.

Carsy

Good to see someone who is convinced that MB never make a design mistake!!

The car only started once during my drive so I did not notice whether it was cranked by the starter motor or not.I was too keen to know whether it would start by itself!!

I would be very grateful if you could explain to me in detail how the alternator would start the car.It would have to be switched into motor mode & drive through the aux belt!!?

I cannot see the fuel saving benifit in warmer countries where A/C is required a good % of the time.

Reading the report ,I understood that the fuel savings was brought about by the new 7 speed ATM in the C Class diesel.

Looking forward to hearing more from your research.

bnam

The Opel Vectra that I used in while abroad used residual cooling from the AC when the car was switched off at (say) traffic lights. It's enough for a couple of minutes in 90+ weather.

Having driven a Prius for several years, I am a fan of the start stop. Helps cut down on local pollution (in areas with lots of traffic lights) as well.

jctevere

There are essentially three main parts involved in an idle-stop system: the gasoline engine, an electric starter/generator and a battery. The transfer of energy works in that order, both forwards and backwards -- it just depends on what state the car is in. When the car's engine is on and you're just about to brake, stop-start systems use regenerative braking, where rotational energy from the wheels turns the electric generator and creates electricity. The generator sends electricity to the battery where it can be stored for later use. When the driver applies the brakes, however, the generator shuts off the gasoline engine. Pressing the accelerator pedal starts the engine once again by taking the stored energy from the battery and running it through an electric starter.

Now, I'm not sure about mercedes' start-stop features, but I would imagine it would be similar to most others, and classified as a "mild hybrid".

EDIT:
It actually appears that mercedes uses a slightly different system, for their detailed page visit:
http://media.daimler.com/dcmedia/0-9...0-0-0-0-0.html

Carsy

Excellent information.

So significant modifications have been made including upgrading the starter and an extra battery. Interesting logic also.

Anyone know about the starter upgrade ?.

The complexity of the modern car is increasing. Where will that all lead regarding maintenance & replacement costs.

The world is awash with natural gas. Why can't we keep car systems simple & affordable by throwing the development money into perfecting its use?

jctevere

It will, eventually. But there is still way too much money to be made with current methods and lobbyists wouldn't have it.

venchka

Golf carts have been operating like this for decades. Probably a much simpler system, but the principle is the same.

Natural gas rocks!

Wayne
Petroleum has been funding my habits since 1980.

VaclavSV

Can you turn it off?

Petje

Yes you can turn it off, i hate the start stop function, i always disable it

JaCe88

I actually really like the start stop function. At first I thought it was both useless and gimmicky but you learn to drive in such a way that you can control whether it is activated or not (without relying on the permanent switch in the centre console). It startles passengers but it does have some major benefits:
1. No diesel engine sound/smell at traffic lights
2. Saves petrol (because obviously being stopped with engine running is a waste of petrol)

As for the cost of repairs in the future, I rationalised it based on the fact that MB has put it in their volume sales car, and it's covered by my MB corporate pricing/included service & warranty. I'd say the cost of fixing it in the future would be negligible anyway (although I did come from a modified Evo X).

RLE

Yes.