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I'd lean against doing it on a normally functioning drivetrain.

"In the old days", people suggested doing this to avoid heat buildup and fluid shearing when sitting in gear.

Electronically controlled engines idle lower, clutch packs properly disengage to allow low impedance fluid flow, etc. I think you cycle more things in the valve body and clutches when you constantly shift in and out of gear, resulting in wear of a different type.
 

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On my motorcycle my habit is shifting to neutral to avoid wear on my clutch pack. Your doing the opposite. Both negligible. But if not, remember, motorcycle clutches are easy and cheap to fix.
 

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Thanks Fibber.
@circus, I thought it has the clutch too in the auto transmission.😁
there’s really not a clutch in an automatic, it has a torque converter, which is basically 2 discs ( one attached to the motor and one attached to the transmission ) that are spinning due to the friction of the fluid. When idling, the engine does not spin the disc enough to produce enough fluid friction to spin the other disc. So it basically just spinning in the fluid and not much else is happening. Of course this is a very simple explanation.
 

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there’s really not a clutch in an automatic, it has a torque converter, which is basically 2 discs ( one attached to the motor and one attached to the transmission ) that are spinning due to the friction of the fluid. When idling, the engine does not spin the disc enough to produce enough fluid friction to spin the other disc. So it basically just spinning in the fluid and not much else is happening. Of course this is a very simple explanation.
Good point about the torque converter, but there are clutches which engage when you shift to drive from neutral, with the resulting impact load on the gears. I used to do the neutral thing until a fellow gear engineer pointed that out.
 

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Discussion Starter #8
"......there are clutches which engage when you shift to drive from neutral....does that mean the clutch engaged while the.car stop?
 

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It’s not the same clutch action as in a manual. Those cliches engage the gears the go forward or backwards. But they are driven by the turbine (disc) of the torque converter that is on the transmission side. So when you are parking, that disc is not spinning but the fluid in the torque converter is not spinning enough to produce enough friction overcome the brakes to spin that disc so the clutches are not spinning the gears.
The easiest way to explain this is that there is actually no mechanical connection at all between the engine and the transmission, it’s a fluid coupling. So when you are at a stop light, there is nothing that is spinning the transmission, even though the engine is running. It’s only the fluid inside the torque converter that is spinning. The fluid produces friction to spin the transmitting, but the engine is spinning so slow at idle that the friction produced by the fluid is not enough to turn the transmission so the fluid just swirls around inside the torque converter. It’s the same concept as an old water mill or wind mill in ancient times. The water or wind would turn the wheel, but only if there is enough flow. When the water or wind flow is low, it’s not enough to overcome friction to turn the water mill or wind mill. Same exact concept except the wind flow or water flow in this case Is produced by the turning engine. At idle THERES not enough to turn the transmission. It when you rev the gas, the engine turns faster producing more flow in the fluid in the torque converter to turn the transmission

Here is a very good video on how torque converters work

  1. How torque converter works.
 

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While at idle you are certainly below the converter stall speed and the lockup clutch is out of the picture. But there is still torque transfer thru the converter/stator. If there wasn't any, your car would not creep forward in gear with your foot off the brake. Nor would it hold position on it's own on a minor hill.

The clutch packs for 1st gear are also engaged (not to be confused with a manual transmissions clutch which replaces the torque converter of an automatic transmission). Still, the system is designed to handle it and keep the fluid cool.

If you are going to sit there for a long time, then sure, shift into neutral. Every time? Leave it in gear.
 

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A non-technical reason not to put it into neutral is for safety. If you were somehow able to see and react fast enough to accelerate out of the way of say... an out of control semi. (My reflexes are too slow - I would still just sit there and get hit)

This is probably a likelier scenario and more important on a motorcycle, i.e. don't do like @circus. OTOH, I find it a literal pain to hold the clutch lever in at a long light so I usually put it in neutral too.
 

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What everyone else said, plus you're spinning the engine faster, using more fuel and probably causing more wear. It's not particularly designed to idle in neutral for extended periods, either: it should be fine, but if they did a shedload of endurance testing at idle, I'd bet most of it was in gear.
 

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I don't change to neutral at traffic lights as we live in a small town and the lights change pretty quickly. (Driving from one side of town to the other takes about 10 minutes!)
I do put it into neutral when queued up at customs as that can be 2 - 4 minutes between moving, and for much of it there is a slight downhill slope so the car rolls along at the appropriate snails pace for customs.
I like the idea of not heating up the auto fluid unnecessarily, but I agree that it just moves the wear and tear somewhere else.

I had a Renault Laguna that had an auto gearbox that dropped into neutral automatically when the car was stopped and your foot was on the brake - when you took your foot off the brake it changed into gear. That system worked well.

If only I could convince my wife that she shouldn't change into drive too quickly when changing from reverse - she is often going backwards slightly when the drive engages. That probably causes more wear than swapping from drive to neutral at the lights.
 
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