transmission neutral engine off

I've been shifting the automatic into neutral at stoplights for years and
turning off the engine on long lights (those I know are a couple of minutes)
where I do that simply for fuel efficiency.

I've never had a transmission repair (multiple vehicles) but I've also never
kept a vehicle for more than 200K miles or so (so I wouldn't know if the
tranny or engine died thereafter).

I just wonder if there is any known clear cut detrimental effect on either
the engine or the transmission from doing this. I don't want to talk about
legal aspects as I know them inside & out as does everyone).

I also can "assume" (yes, I know) that there's "wear" on the engine and/or
transmission from more cycles to the engine and more shifting on the
transmission, but is there a DIRECT negative effect on either?

Only someone who knows of a DIRECT effect other than general wear and tear
(which we all know about) would be able to answer this question I think.

I ask not because I'm going to ever change my habits as it works for me,
but to simply learn if there is any DIRECT effect on wear you know of.

On 20/3/21 1:27 pm, Robin Goodfellow wrote:
> I've been shifting the automatic into neutral at stoplights for years and
> turning off the engine on long lights (those I know are a couple of minutes)
> where I do that simply for fuel efficiency.
>
> I've never had a transmission repair (multiple vehicles) but I've also never
> kept a vehicle for more than 200K miles or so (so I wouldn't know if the
> tranny or engine died thereafter).
>
> I just wonder if there is any known clear cut detrimental effect on either
> the engine or the transmission from doing this. I don't want to talk about
> legal aspects as I know them inside & out as does everyone).
>
> I also can "assume" (yes, I know) that there's "wear" on the engine and/or
> transmission from more cycles to the engine and more shifting on the
> transmission, but is there a DIRECT negative effect on either?
>
> Only someone who knows of a DIRECT effect other than general wear and tear
> (which we all know about) would be able to answer this question I think.
>
> I ask not because I'm going to ever change my habits as it works for me,
> but to simply learn if there is any DIRECT effect on wear you know of.
>
There is a negative effect on the transmission. When you are in any fwd
gear, in general, the fwd driving clutch is engaged and it remains
engaged whilst ever you are in D, L 1, 2 or 3. By shifting to neutral
you are releasing this clutch and reapplying it when you reselect drive.
What can, and does, happen is that you get fatigue failure of the
diaphragm plate return spring. This one in a BW35 trans;

https://images-na.ssl-images-amazon....zU7iL._AC_.jpg

There is literally no point in shifting to neutral other than to create
fatigue failure of this spring. Any fuel savings will be miniscule at
best and it should be noted that drag in the torque converter will not
be an issue. The other point is that it is an extra step - re-engaging
drive - that will delay your launch.

Note, not all autos use a diaphragm spring in the forward clutch. Some
use a series of coil springs. These are less prone to fatigue failure.

--

Xeno


Nothing astonishes Noddy so much as common sense and plain dealing.
(with apologies to Ralph Waldo Emerson)

Xeno > asked


> By shifting to neutral you are releasing this clutch
> and reapplying it when you reselect drive.

Thank you for understanding the question to give technical answers
specifically about direct wear tradeoffs for rolling in neutral for long
distances and for shifting into neutral (or turning the engine off) at long
lights.

> What can, and does, happen is that you get fatigue failure of the
> diaphragm plate return spring.

Ah. This is good to know. I will check to see what kind of transmission I
have to see if it has coil springs or a diaphragm plates (as I've seen in
manual transmissions).

> There is literally no point in shifting to neutral other than to create
> fatigue failure of this spring.

Well, I know it worked in a half dozen cars (up to ~200K miles at least).

But there are always tradeoffs.
That's why I had asked for direct wear.

1] I assumed rolling for miles downhill reduces transmission braking wear
2] Of course it shifts that heat wear to the brakes (much easier a repair)
3] Certainly engine shutoff at long lights has an on/off wear tradeoff
4] The question is whether 1-1/2 to 2 minutes meets that tradeoff time?
5] Certainly engine RPM drops from D to N at standstill during long lights
6] The question is the tradeoff in efficiency versus direct tranny wear?

I've seen a contrarian view but my experience doesn't match it though
https://www.mercurynews.com/2014/05/...drivers-do-it/

> Any fuel savings will be miniscule at best and it should be noted that
> drag in the torque converter will not be an issue.

Shutting off the engine at long lights "should" have a tradeoff time
where the question becomes what's the fuel savings & low oil pressure
tradeoff time for a warm engine restart?

Likewise leaving the vehicle in Drive versus Neutral must have a tradeoff
time although the fuel savings will be less as engine RPM is not zero.
has a tradeoff time.

> The other point is that it is an extra step - re-engaging
> drive - that will delay your launch.

No problem. These predictable long lights I know rather well so I know
exactly how much time I have when the last set turns colors such that I've
got the engine started & the shift in drive seconds before my own light
finally turns green.

The key question is how two and a half minutes of a warm on/off
engine/transmission cycle compares to idling in drive (or neutral)
in terms of directly related on/off cycle wear & efficiency.

> Note, not all autos use a diaphragm spring in the forward clutch. Some
> use a series of coil springs. These are less prone to fatigue failure.

I've been doing this for decades and never had a related engine or
transmission repair but that doesn't mean anything in and of itself.

It just means it's not deadly but directly related wear and tear could still
be happening but I think there's wear and tear in both situations.

The question is only one of technical tradeoffs in terms of direct wear and
tear (I'm not worried about legal/safety tradeoffs for this question).