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;
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._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.
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.
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).
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
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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.
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.
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).
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