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Discussion Starter #1
I think after dredging the net for the answer, this is probably not an easily answerable question...

But, as I couldn't find anything BMW specific- here goes:

First time with a BMW with auto transmission.

The guy at the (non-BMW) dealership said to leave it in drive when you're at a red light?

It feels weird doing that- as the car wants to go.

So it feels like you're suppressing that and doing damage?

But he said the car will regulate itself down- or not be pulling if the brake is applied.

I guess this comes down to the car. Presumably it's engineered to be left in Drive all the time, foot on the brake when necessary?

This is a 330E, if that makes any difference at all. Thanks everyone!
 

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I leave the car In drive and hold the brake, unless I think I am going to be stopped for a longer time than a few minutes ie. Traffic jam, extremely long traffic light phases,etc.
 

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As bratty above - I leave all mine in drive unless I know it's going to be a reasonably long stop (as in proper traffic jam - I wouldn't bother putting it in neutral for a traffic light).

More important is to get the gearbox fluid and filter changed every 60k miles.
 

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Discussion Starter #5
Thanks everyone- really helpful.

And this car will know all of these things re servicing right? For example the gearbox fluid ^ ?
 

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No - gearbox service won't show as BMW say they're sealed for life but the box manufacturers say 60k and they're right.
 

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And remember just the right foot.
See many auto's setting off with the brake lights still on so must have there left foot on the brake.
I know an old school mechanic in his late 50s and he does it with any auto he moves around the garage.
 

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Interesting. E90 320d automatic can I just ask please, when driving (I do a lot of motorway) at speed on high revs and I get to a significant stretch of slope I sometimes switch to N and let the car roll down at speed. You can see the revs drop. I've found it rolls easier and faster as opposed to just easing of the pedal but the car is still in gear, and also helps with petrol consumption. Am I doing any possibe damage at all by coasting atimes in neutral?
 

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It's not good practice from a car control perspective and when you re-engage drive you are putting stress on the clutch packs as they have to re-engage at speed. So not something that is recommended...
 

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It's not good practice from a car control perspective and when you re-engage drive you are putting stress on the clutch packs as they have to re-engage at speed. So not something that is recommended...
Ah right I see. Thanks much
 

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Ah right I see. Thanks much
It will use more petrol in neutral than in drive with no accelerator. Cars use almost zero fuel when engine braking, plus you then need heavier actual braking to slow the car down.
So you are using more fuel and wearing out your brakes faster.
 

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It will use more petrol in neutral than in drive with no accelerator. Cars use almost zero fuel when engine braking, plus you then need heavier actual braking to slow the car down.
So you are using more fuel and wearing out your brakes faster.
Really? I'm surprised to hear that. When I put it in neutral the rev counter drops to the lowest it can with the engine running, pretty much same as when idling. About 500 rpm iirc? Certainly under a thousand. When it's on drive with foot off the pedal it never seems to drop below 1000. At times if on high gears at speed it can settle around 2000 rpm even with foot off but in D.
I would have thought with coasting you certainly save on some fuel. BMW even recommend coasting when on high gear to save fuel though that was for manual cars. Dunno if they recommend it for automatics.
I was just wondering if I may be doing other damage over time such as the gearbox from continually shifting an automatic, clutch plates etc that over time might outweigh the benefits of a little fuel saving
 

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Really? I'm surprised to hear that. When I put it in neutral the rev counter drops to the lowest it can with the engine running, pretty much same as when idling. About 500 rpm iirc? Certainly under a thousand. When it's on drive with foot off the pedal it never seems to drop below 1000. At times if on high gears at speed it can settle around 2000 rpm even with foot off but in D.
I would have thought with coasting you certainly save on some fuel. BMW even recommend coasting when on high gear to save fuel though that was for manual cars. Dunno if they recommend it for automatics.
I was just wondering if I may be doing other damage over time such as the gearbox from continually shifting an automatic, clutch plates etc that over time might outweigh the benefits of a little fuel saving
I'm not going to give a lesson in thermodynamics but the revs have absolutely nothing to do with fuel economy when going downhill (or any other time for that matter). A gigantic ship engine revs at just a few hundred rpm but uses tons of fuel per hour.
Do some research and you will see that you are using much more fuel coasting downhill than using engine braking. Note that electric cars are different so this only applies to combustion engines (although electric cars will use the phenomenon to recharge the battery at this point).

BMW coasting mode is only relevant for small declines or flat.
 

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I'm not going to give a lesson in thermodynamics but the revs have absolutely nothing to do with fuel economy when going downhill (or any other time for that matter). A gigantic ship engine revs at just a few hundred rpm but uses tons of fuel per hour.
Do some research and you will see that you are using much more fuel coasting downhill than using engine braking. Note that electric cars are different so this only applies to combustion engines (although electric cars will use the phenomenon to recharge the battery at this point).

BMW coasting mode is only relevant for small declines or flat.
Hi Ste42. Thanks for your input. To my understanding after doing some reading, it would seem more to do with the 'mechanics' than thermodynamics (re cars). A car coasting in neutral will use less fuel than a car accelerating, even lightly, as it's drawing more power, feeding the engine more fuel, revving harder whilst accelerating. Coastting downhill would effectively be using aroung same fuel as idling, a little, but using fuel nonetheless. I think the disadvantage of coasting in neutral, and this is down to ECUs in modern cars as opposed to the old carburators, comes when compared to coasting in gear when the ECU is sending no fuel to the engine at all, as opposed to 'little' fuel being used when coasting in neutral. Which is what you concluded on that and I agree. I don't entirely agree with the view that a higher revving engine isn't using more petrol than one that is idling. In any case, effectively it is better to coast in gear than neutral from a consumption point of view. Coasting in nertral might be more economical in certain circumstances such as if you build enough momentum and then don't have to accelerate to climb up a small hill. This is regarding fuel economy alone of course, without regard to effects on gearbox, car control etc.
This is my understanding now at least. In which case I will just ease off the accelerator but still in gear when needed and conducive.
All rather interesting and thanks again for the input
 

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There is a caveat to coasting. On the newer autos, around 17 and newer a coasting feature is built into the gearbox and you can enable it in the iDrive for eco pro mode.
 
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