Audi stop-start facility

**fiddler3** · 15-09-2013,09:47 AM

I am interested in the views of others into the default setting where the engine stops automatically and starts again when clutch is depressed and gear engaged. I switch off this facility as it seems strange to have the starter motor operating so often in heavy traffic. I am also uncertain as to its overall effect on reducing emissions. I welcome comments on this from those who also have this facility and whether or not they favour its use.

Cheers

David

**johnsimcox** · 15-09-2013,12:11 PM

Originally Posted by fiddler3

I am interested in the views of others into the default setting where the engine stops automatically and starts again when clutch is depressed and gear engaged. I switch off this facility as it seems strange to have the starter motor operating so often in heavy traffic. I am also uncertain as to its overall effect on reducing emissions. I welcome comments on this from those who also have this facility and whether or not they favour its use.

Cheers

David

Use it all the time and have no problems with it all. In a recent Autocar longterm test, one of the cars they had (think it was a Kia o Hyundai) actually recorded the amount of time the engine was off with Stop/Start system. If I recall correctly over the 12 month period they had the car the engine was off for something close to 24 hours. Think how much fuel you would burn leaving the car to idle for 24 hours and I think it is pretty certain the system is saving both fuel and reducing emissions. Also look at the fuel consumption on the DIS drop as the car is sitting in traffic. Some will say that it burns more fuel to restart the car, but as it only operates when the engine is at a reasonable temperature this is not a real issue. Find it strange driving other cars that do not have it available

**boof** · 15-09-2013,07:57 PM

I'm on my second car with the system.

I was nervous / concerned about it before hand but ended up having no issues at all with the first car (BMW) and so far no problems with the A6 either.

My understanding is that the car systems are designed around the increased duty cycle and that many clever things go in the background to 'park' the engine allowing for minimal fueling on a restart.

All in all I don't even notice it anymore, it's second nature. I'm only reminded of it whe I have passengers who are not used to such a system and get concerned that the engine has suddenly cut out...

I have no science to back up emissions / mpg figures but it seems logical to me that the engine being switched off whilst not in use is far preferable to it being on and burning fuel.

In a few years time we'll all have cylinder deactivation common place as well I imagine!

**harryg** · 15-09-2013,08:03 PM

How does this effect the turbine in the Turbo? this beast is spinning at about 20,000 RPM engine, engine stops and (oil pump is engine driven I take it) no oil feed to compressor/turbine bearings. Imagine busy period and car stopping and starting in heavy traffic how does lubrication feed turbine bearings...........Learned in merchant navy that you never stop a turbo diesel on full load but bring it down slowly to idle before stopping.
I always disable stop start due to this problem.

**Guest 2** · 15-09-2013,08:06 PM

Originally Posted by harryg

How does this effect the turbine in the Turbo? this beast is spinning at about 20,000 RPM engine, engine stops and (oil pump is engine driven I take it) no oil feed to compressor/turbine bearings. Imagine busy period and car stopping and starting in heavy traffic how does lubrication feed turbine bearings...........Learned in merchant navy that you never stop a turbo diesel on full load but bring it down slowly to idle before stopping.
I always disable stop start due to this problem.

I think the engineers at Audi have took into consideration the turbo and starter and the car probably have fail-safes should the car be stuck in traffic etc and there is constant on and off. If SS was going to cause damage to the turbo then no-one would use SS and wouldn't be invented?

**boof** · 15-09-2013,08:12 PM

I suspect the oil pump is electric. And / or turbos likely water cooled as well?

The problem you describe would also require you to idle the car at the end of a journey to let the turbo cool. Perhaps on a highly modified and high strung performance engine but otherwise that shouldn't be necessary in a modern car.

These were all concerns I had as well but I came to the conclusion :

- The info that's out there on some of the systems answers the questions.

- Ultimately there's no way they'd manufacture a car with that inherent an issue. If I can identify it as a problem then engine engineers who are 1000x smarter than me have fixed it before breakfast.

- Stop / start isn't a binary function. The car will only shut off if any number of parameters are within tolerance. I can well imagine this includes temperature / pressures in the cooling system for the engine and turbo.

Of course the other question you should ask is that if all the turbo etc components have been designed to have a shorter overall lifespan as it's assumed they will not be in service as much due to stop start. Therefore by disabling the system you're causing greater than designed wear. I think I'm joking...

**zollaf** · 15-09-2013,08:32 PM

the turbo is fed oil from the engines oil pump which is driven by the engine so indeed when the engine stops oil stops as well. a turbo will spin at speeds in excess of 200,000 rpm ( yes, two hundred thousand) when going flat out. you should indeed let a turbo'd engine idle before shutting it down after using the turbo. in traffic you are not using the turbo so no need to idle as the engine is only really on or just above idle. the problem is not the speed or the turbo though but the heat it generates. if the unit is glowing cherry red and you switch the engine off, the oil in the turbo burns and forms carbon. do this too many times and say goodbye to your bearings. so if you have been ragging it then hit traffic its not good if the ss turns the engine off. but for most everyday driving it won't cause a problem. how many people don't treat a turbo properly anyway and have them blow in 50k miles ?

**ukgroucho** · 15-09-2013,09:15 PM

I can see how S/s works in cities or in a queue on the motorway but it drives me nuts when I drive around the country lanes that surround me. It is a pain in the whatsit when you arrive at a T junction and all is clear so you put your foot down just as the engine stops. I turn it of as a matter of course.. part of my heading out of the driveway ritual.
Plus I do wonder about wear and tear on batteries and starter motors...

**zollaf** · 15-09-2013,09:17 PM

oh man, that must be soooo annoying then in the country. as you say its fine for where it was intended, the city. i wonder how long before accidents are caused by it.

**ukgroucho** · 15-09-2013,09:45 PM

YUP... and it is one of the few "settings" that the car does not remember between start-ups...
It's a lovely (REALLY lovely) car but there are a few technology decisions that Audi made that may not be aligned with the desires of their customers.. I suspect the s/s one may be policy driven from the perspective of gaining specific fuel consumption ratings.