D Or N When Slowing Down ?

[simontaylor]

Hi, new to Lexus Ls400 and only my 2nd outo car .

When coming off the motorway, or down a long hill, and up to red lights, I like to pop the auto into N and enjoy reduced petrol consumption at idle speed often for .3 or .4 of a mile. :D

Sometimes I'll coast to a stop and other times pop it back into D at 30 mph or something.

For my 100mile commute trip, I can be doing this bout 10 times wich is a free-"ish" 3 or 4 miles in a day. :D :D :D

Is this a bad thing for the autobox?

Some one told me that it is not good for the torque converter.

Look forward to some comments and links to auto box web sites maybe. :mat:

Thanks in advance.

[SHAHZ]

You use more fuel when coasting

[Kremmen]

Putting an Auto box in neutral when coasting used to be a definate no-no. Whilst in this mode the auto fluid is not lubricating the internals as it should and you could lockup the gerabox.

This is the reason why tow trucks never tow an auto with the drive wheels rotating on the ground.

[MrADeveci]

I'm sure colin will be along shortly ... and explain the technical side of it ......... but as far as I know ...... when the car is in D ..... and you take your foot off the accelerator .... there is a fuel cut out that kicks in .... which is more econimical then leaving it in N

In fact ..... you can try it, I have done it before.

Run your car ....... so it's at the normal temperature.

STOP ............. just by pressing your brake (in D) .... and watch your rev ometer.

Then, still pressing the Brake ....... pt it into Neutral.

You will notice the revs actually work higher ! ;)

[aido]

Colin Barber said months ago something along the lines that a car uses more petrol when in neutral than when in gear coasting, that might have been in relation to a manual so not sure of the auto effects like Kremmen mentions above, I just leave my manual box in gear a lot more now than I used to!

[MrADeveci]

Aido ... it was in relation to an auto mate .........

[aido]

Oh right, guess a question for Colin when he comes along would be is the manual the same principle?

I could do with an auto at the minute, my hand keeps dying on me when I'm driving so I end up driving through 30's in fifth, not a nice experience

[kam05]

With a manual box you can use the gears to brake, (low gear, high revs help slow you down), does the same theory not apply to autos?

[MrADeveci]

With a manual box you can use the gears to brake, (low gear, high revs help slow you down), does the same theory not apply to autos?

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Nope ...................

[kam05]

With a manual box you can use the gears to brake, (low gear, high revs help slow you down), does the same theory not apply to autos?

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Nope ...................

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I didn't think so........... :)

[Kremmen]

With auto's there is a small bit of braking but nothing to write home about. I have read somewhere that there used to be some asbestos parts within the auto gearbox to help introduce slight braking (on some models).

One thing I have never done with any auto is dropping a cog manually to produce some braking. I suppose brake pads are cheaper than a new torque converter.

As far as fuel saving goes it's not the auto that does the business but the fuel injector.

In the old days when carburettors were the norm lifting your foot off the loud pedal had no effect on fuel saving because the engine still opened the carburettor swivel. As a result air rushing past the venturi still dragged fuel from the tank.

Fuel injection does actually close off the fuel system completely and in the early days caused damage because the upper engine was no longer getting lubricated by petrol. Lengthy coasting would produce excessive valve and associated components wear.

[MacRS200]

One thing I have never done with any auto is dropping a cog manually to produce some braking. I suppose brake pads are cheaper than a new torque converter.

←

I do it regularly with the tip going into corners and roundabouts to avoid "kick down" when you floor it on the way out, and you do get more engine braking.

Figure that it won't do any damage as the tip won't let you change down if the revs will be too high and I assume the same for gear train stress applies.

[lexicon]

I'm sure colin will be along shortly ... and explain the technical side of it ......... but as far as I know ...... when the car is in D ..... and you take your foot off the accelerator .... there is a fuel cut out that kicks in .... which is more econimical then leaving it in N

In fact ..... you can try it, I have done it before.

Run your car ....... so it's at the normal temperature.

STOP ............. just by pressing your brake (in D) .... and watch your rev ometer.

Then, still pressing the Brake ....... pt it into Neutral.

You will notice the revs actually work higher !  ;)

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That's because in D it's loading the Torque Converter which pulls the revs down a bit, whereas in N it isn't - nothing to do with fuel-cut. If stopped you should select N as it will use less fuel and be better for the TC.

On overun (slowing in-gear) you will benefit from the fuel-cut.

[MrADeveci]

Where is colin when you need him ! ................. ?

[lexicon]

Where is colin when you need him ! ................. ?

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Hmmm, I thought I was being clear enough;

On overun (coasting/slowing) in D you will benefit from the the fuel-cut that would not happen if you were in N (when fuel is being used just to keep the revs "up" at idle speed).

However, if you are STOPPED you will use more fuel in D as there is a load on the engine from the Torque Convertor.

So, the difference in revs you describe is due to reduced load in N, not because of fuel-cut in D.

Loading the TC unnecessarily (ie foot on brakes at lights etc) increases temperatures/wear, plus it will use more fuel.

Does that make sense?

[MrADeveci]

Hmmm, I thought I was being clear enough;

Yes, you are making your self clear enough, don't know if that was saarcatic or not .... but anyway.

I said Where's Colin when you need him, as he is always full of knowledge ... and I'm sure I remember reading something he posted before, that contradicts what you have just said ............

I'm sure he will be along shortly !

[lexicon]

Hmmm, I thought I was being clear enough;

Yes, you are making your self clear enough, don't know if that was saarcatic or not .... but anyway.

I said Where's Colin when you need him, as he is always full of knowledge ... and I'm sure I remember reading something he posted before, that contradicts what you have just said ............

I'm sure he will be along shortly !

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No, not being sarcastic.

As far as I know, it works the way I described it.

I'm always prepared to learn from others though.

On another point, you CAN use lower gears for engine braking - if on a long enough hill this would be better than arriving at the bottom with overheated brakes.

If you drive off-road with an auto you will definitely want to do this.

[Straight-Six]

Interesting topic....Would be nice to know the definitive answer as any help on fuel consumption would be great

As for the engine braking,i always try and use the d---3----2-----L as much as possible to save the brakes,i would have thought that was the main reason they were there

I was always told to use N when sitting at junctions as it saves the engine...don't know what the hell that means but i do it

*shuffles off to find Lexus manual*

[Matthew_McNally]

as several people have pointed out - its not a good idea to change to N and coast.

There is however a benefit to shifting into N once you are stopped. This shifts out of gear, and on a level surface means may not have to sit holding the car on the brakes, as leaving hot brake pads on your disks is not a good idea.

If its not a level surface, then shift into P, or apply the footbrake.

As for the engine braking,i always try and use the d---3----2-----L as much as possible to save the brakes,i would have thought that was the main reason they were there

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so - you increase the wear on the engine to save the wear on the brakes?

Which of these items do you think are consumable parts, designed to be replaced? And which do you think is the cheapest to replace? :D

[Jiberjaber]

With a manual box you can use the gears to brake, (low gear, high revs help slow you down), does the same theory not apply to autos?

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Nope ...................

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Yes you can use the gears to provide engine braking on an auto, however you must actualy put the selector into a lower gear for it to work.

If you have cruse on, you can go from D to 3 and still have the cruse set and also have some braking.

If you go to anything less than 3 it will cancel the cruse setting.

2 gives more brake than 3 which gives more brake than D.

There is a section in the owners manual which tells you how much engine braking you get (as a %) in each gear selection.

HTH :)

[MrADeveci]

Hmm ... having re-read the thread ... I don't know why I said you Don't get engine braking from an auto .... because you do ?!

OH well .... my bad ..............

[Jiberjaber]

[Rillo]

You should NEVER put an auto into N to coast...

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this would mean you have to put your sandwich down and get crumbs everywhere :D

[chips229]

You should never put a Auto in N when coasting as it can damage the autobox and theres a chance,not as much a chance nowadays with the gear selector in a staggered slot of selecting R or P,with the older autos the selector moved just in a forward/backward motion.

As to engine breaking on the computer controlled autoboxs they have a safe downshift speed sensor so if the cars going to fast for the gear pre selected then it wont shift down to that gear until the speed/engine rpm are safe to do so.

Cheers chips.

[tonupkid]

Im with Lexicon on this one. Read him and believe!!

Another reason why you should not coast your car in neutral.

OK This bit's going to be a bit hard for everyone to swallow, here goes.

I've never had a Lex stall, but if it did while you were coasting in N. Well first you'd loose your powered steering, and then after a little light braking you'd find you also had no braking assistance.

Have you ever tried this? If you were to be towed, by say the AA. OK I know this is impossible in a Lex so have a laff if you want. But if you have been unfortunate enough to be attached to the basck of a tow truck in a big car, and I have (nope it wasn't a Lexus). Its VERY HEAVY. Not the steering and braking you want as your bating up to a school crossing.

Big cars I've been towed in. BMW 7 once and various Grannies and Vauxhalls, more times than I wish to remember. I gues thats why I'm so happy to have a Lexus sitting on my driveway tonight.

Cheers

Nick