Question for an auto gearbox expert

[shawn]

is it a problem to slip in and out of neutral when a long period of costing are possible ?

 

The reason I ask is that I have some roads around here where I can easily just roll along for a mile or so,

I have usually had manual motors and I would push the clutch in and save myself petrol.

My Alphard is auto and im now in the habit of knocking in into neutral when I want to cost downhill,

a recent passenger of mine said i could damage my gear box doing this .

 

What say you ?

 

[Rojie]

Hi Shawn,

 

I am no auto expert but have driven autos for 30 years, or more.

 

IMHO, it is not a good practice to coast an auto gearbox.

I am sure I read somewhere why (but cannot remember the reason).

 

Similarly, and possibly for the same reason. vehicles with autos should not be towed with the drive wheels rotating.

 

Hopefully an auto expert will explain whether it is OK, or not.

 

With injected engines you won't be saving much fuel as the fuel is virtually switched off on engine overrun.

[shawn]

Thanks mate.

I read in the manual not to coast downhill, but it explains the reason for that advice is the loss of engine breaking in an emergence could be dangerous.

Well that don't bother me as my breaks are great, and I can always slip it back in gear if I need.

As for the petrol saving – I notice the rev counter drops all the way down to tick-over when I knock it out of gear.

Also when in gear the engine drag slows me down a little when im not using the accelerator.

 

For example- I have a down hill road near me that is about one mile long, if im doing 40mph at the top and coast, ill still be doing 40 at the bottom.

But if I leave it in gear the rev counter will be double what it is on tick-over & the engine drag slows the van to the extent that I will need to occasionally apply slight pressure to the accelerator peddle to maintain 40mph

 

Its a quandary

 

thanks for you thoughts on the matter

[Rojie]

Hi Shawn,

 

Can I speculate on this a bit more.

I have another car which, unlike Alphies, has a computer that advises instant fuel consumption.

 

The rev counter advises the revolutions the engine is experiencing. It doesn't advise the fuel consumption.

So, in your case, it doesn't follow that you are using more fuel; just that the engine is turning more rapidly.

Which it will be as you are moving downhill. The ECU will virtually shut of all the fuel during your mile long coast.

 

The other issue, I have read, concerns oil circulation; both in the auto gearbox and in the engine.

Unlike the fuel, engine oil circulation is controlled by the engine speed. I don't know whether the auto oil is, or is not.

 

My view is, not that it is dangerous, just unnecessary to coast.

But, as my dear old Dad used to say, "Brakes are cheaper than gearboxes"

 

Whatever you decide, HAPPY MOTORING.

[shawn]

That is helpful .

I was previously assuming the revs related directly to fuel consumption.

thanks.

[Colin04]

in a modern fuel injected engine you will actually use more fuel coasting as the injectors need to give enough fuel for idle. if you are on overrun, no fuel is needed.

[shawn]

wow

thanks Colin

[shawn]

On the whole my auto gear change is very smooth on my van.

Recently iv started feeling the gear change between 1^st & 2^nd and 2^nd & 3^rd when accelerating slowly in the mornings.

I don't feel it as much when the engine is warm, and I don't think I felt it as much in the summer.

?

[Rojie]

My guess is, this is just cold auto oil.

 

Have you checked the auto oil level ?

 

Autos do need oil changes from time to time, and the filter.

Someone on here recently did an oil / filter change, but I don't know why. I'll try and find them and ask

 

As we don't have Service manuals yet, it is difficult to know when we need to change the auto oil.

[shawn]

oil level is good and it looks clean.

The gear change bump is very slight and not a problem , I will worry if it starts getting worse.

 

[Rojie]

Most autos give a little 'bump' when changing.

The harder the acceleration or retardation, normally the larger the 'bump'.

In my experience, the smaller the engine the larger the bump!

 

Have you driven automatics gearboxes before your Alphie ?

 

Yours should be a 5 speed and quite smooth. (I am talking V6 here).

 

I have another car which has a very expensive auto gearbox and that has a 'slurring/slipping' effect when changing (unless your driving style is foot to floor then there is a jolt as the box shifts quickly).

 

As you say, wait and see.

 

Perhaps other Alphie drivers will comment.

[shawn]

2 hours ago, Rojie said:

Have you driven automatics gearboxes before your Alphie ?

My auto experience is very limited.

In fact I drove this Alphard around in 3^rd gear only for the first couple of months and wondered why it was revving so high on motorways

There is a thread on this forum titled “70 MPH = 4000 Revs ?”

I shouldn't have reminded anybody about that really because its embarrassing 😡

Ill get my coat

[Rojie]

I have a 2006 5 speed auto.

 

If I were to fault the car; it would be the gear selection !

Compared to all other autos I have ever driven ( a lot, as I lived in the US twice) it is quite agricultural.

 

I am speaking of the gear shift, not the auto gear changes themselves.

 

Many people who have not driven autos can struggle when challenged by an auto.

They are easy. Just keep your left foot on the floor; not the pedals !

Like riding a bicycle, or swimming, once you accomplish it you will wonder why you never had an auto.

 

There is a notification of which gear you have selected on the dash.

If in auto, let the box do the work.

Also you can read the JPNZ Owners Manual as it has a section on 'hill driving'.