AT into N or P at red lights

[MrHorspwer]

Most modern transmission already do this.

ZF calls it Neutral Idle Control and all their 8HP units have it. AISIN calls it Automatic Neutral Control. All GM transmissions since the 6Lxx/6Txx have had a neutral idle feature.

The transmission control module releases whatever forward clutch it needs to when vehicle speed is 0, effectively putting the transmission into a neutral state without moving the manual valve or whatever controls the transmission range. Because the torque convertor isn't shearing fluid in neutral, engine load and fuel consumption is reduced ever so slightly. It's a no-cost fuel saving solution that only requires a software strategy to implement.

If you've ever felt a tiny bump while transitioning from the brake to the throttle from a stop, like when you're starting to pull into the garage after waiting for the garage door to open, that's the transmission coming out of neutral idle. It is typically imperceptible on level ground but the slight incline of a driveway makes it just noticeable enough if you're really paying attention.

 

[totegoat]

I put stick shifts in neutral, leave autos in drive.

 

[Hall]

There are a few lights around here where I end up waiting 5 minutes. I will put it in park then.

That's much different than a normal red light which typically cycle every minute or so. In this case, I would do the same, just like I do if I get caught by a train at the very start. In that case, I know it could be a long one so I put it in Park. If I come up to the crossing and the train is already going past, I sometimes put it in park, sometimes not.

The 5 minute light happens when I'm the only vehicle on the sensor, as it won't give a green left turn arrow for just one vehicle. But when others show up, the green left turn happens next cycle.

What happens if you stop farther back ?

In the McDonald's drive through

This reminds of what I see quite often... The car in front pulls up, puts it in Park, and waits. 30 seconds later, puts it in Drive to pull forward, then Park again.

 

[slacktide_bitog]

Some newer cars automatically put it in neutral at a stop, but if your car doesn't do this, it's probably not a good idea to do it.

Most modern transmission already do this.

ZF calls it Neutral Idle Control and all their 8HP units have it. AISIN calls it Automatic Neutral Control. All GM transmissions since the 6Lxx/6Txx have had a neutral idle feature.

The transmission control module releases whatever forward clutch it needs to when vehicle speed is 0, effectively putting the transmission into a neutral state without moving the manual valve or whatever controls the transmission range. Because the torque convertor isn't shearing fluid in neutral, engine load and fuel consumption is reduced ever so slightly. It's a no-cost fuel saving solution that only requires a software strategy to implement.

If you've ever felt a tiny bump while transitioning from the brake to the throttle from a stop, like when you're starting to pull into the garage after waiting for the garage door to open, that's the transmission coming out of neutral idle. It is typically imperceptible on level ground but the slight incline of a driveway makes it just noticeable enough if you're really paying attention.

This.

It will really only save fuel if it's already programmed to do it.

The first GM car I know of to use it is the Saturn Astra (with an Aisin 4-speed auto).

 

[dumkid]

It won't hurt anything to leave it in drive, unless you've been towing with the torque converter unlocked and don't have a factory transmission cooler. (almost all cars do) In that case you should get a transmission cooler

 

[HemiBenny]

Traffic lights or stop and go traffic, I leave it in D.
Waiting for a train or any other stoppage for an extended amount of time, it goes into P once I see that everyone behind me is behaving and stopped as well.

 

[DGXR]

Automatics are designed to leave in gear for normal driving, including long red lights. If you're overheating at a red light, you have bigger problems than your gear selection. Of course, extended idling time should be spent in P or N.

 

[someonesomewhere]

Have used N or P in the distant past when broke and car was having carburetor issues or other tune-up related problems and wanting to die at a light. Just to get through to payday.

 

[MolaKule]

Does putting car into P or N at red lights help extend auto transmission life? '10 Sonata 2.4 original owner 374 k. I don't accelerate hard at all, come to complete stop before R to D.

No, it actually reduces the transmission life.

Have you ever seen an Owner's Manual that tells the owner to do such a thing?

 

[Samik8377]

This is an interesting debate all over the internet and the recommendations vary. With every D -N & N - D movement there is some slippage which eis equivalent to slippage during every gear shift. So by leaving in D you are preventing the werar and tear caused by a gear shift every time. On the contrary, you are heating up the ATF. This additional heat does matter in tropical countries.

For more than a minute's wait, it is advisable to shift to N. In that case getting rear ended won't hurt. Also if left in D with brakes pressed for a while, lapse in concentration can release the brake and cause the car to move forward.

 

[vpr5703]

This is an interesting debate all over the internet and the recommendations vary. With every D -N & N - D movement there is some slippage which eis equivalent to slippage during every gear shift. So by leaving in D you are preventing the werar and tear caused by a gear shift every time. On the contrary, you are heating up the ATF. This additional heat does matter in tropical countries.

For more than a minute's wait, it is advisable to shift to N. In that case getting rear ended won't hurt. Also if left in D with brakes pressed for a while, lapse in concentration can release the brake and cause the car to move forward.

The question is how much heat are you generating if you have a transmission that isn't programmed for idle neutral. My bet is that you aren't generating much heat at all since the engine should be under 1000 rpm. So is the wear on the clutch pack balanced out by the lower heat generated in the torque converter? Personally I doubt it.

 

[Wheel]

Don't really know the answer, but I bang the trans into neutral and take my foot off the brake pedal at almost every stop light (on level ground). Haven't changed a brake light bulb in many years if that helps

Around here, I'd wear out my back bumper cause nobody would know to stop.

 

[Kantaro]

Volvo tried this before with Aisin transmissions and had to issue a software update to disable the feature due to the problems it caused. They called it Neutral Control

Volvo Tech Tip: A/T-Neutral Control Function

A function called "Neutral Control" is present on all 2001 V70 and S60 cars, as well as on 2002 non-turbo V70 and S60 cars built before January 2002. When the vehicle comes to a stop, the Transmission Control Module (TCM) activates Neutral Control. Even though the gear selector is in the Drive...

www.brakeandfrontend.com

 

[JHZR2]

I wouldn’t put it in park, especially if the pumping stops, like on some Chrysler ATs or whatnot. I will sometimes put it in neutral, but not always. The angle of clutches reengaging is an interesting thought.

 

[JohnnyG]

This is what the Start/stop feature was designed to do. Putting the car in neutral isn't going to save you any gas, you'll still get "0" MPG!
On the Mercedes, with start/stop, I don't care what gear the transmission is in. It has two or three ELECTRIC pumps in the transmission that ensures it'll be ready to go when my foot comes off the brake.

 

[MolaKule]

The question is how much heat are you generating if you have a transmission that isn't programmed for idle neutral. My bet is that you aren't generating much heat at all since the engine should be under 1000 rpm. So is the wear on the clutch pack balanced out by the lower heat generated in the torque converter? Personally I doubt it.

I doubt it as well.

Any time you re-engage the wet clutches you will have a momentary and localized heating event at the clutch surfaces. However, the oil that is squeezed out goes back into circulation to be cooled.

Some seem to be ignoring the fact that the oil is being continually cooled.

 

[vpr5703]

I doubt it as well.

Any time you engage the wet clutches you will have a momentary and localized heating event at the clutch surfaces. However, the oil that is squeezed out goes back into circulation to be cooled.

Some seem to be ignoring the fact that the oil is being continually cooled.

I might set out to try and prove this point in my car. If I put my car into manual mode it disables neutral idle. Then just track ATF temperature via ForScan and see if it rises any when the car is stopped at red lights.

 

[MolaKule]

I might set out to try and prove this point in my car. If I put my car into manual mode it disables neutral idle. Then just track ATF temperature via ForScan and see if it rises any when the car is stopped at red lights.

You can try that but the result will be dependent on the where the bulk oil temperature is being sampled.

 

[vpr5703]

You can try that but the result will be dependent on the where the bulk oil temperature is being sampled.

True. And I have no idea where the temp sensor is.

 

[ammolab]

This is also the reason in cars with manuals or on motorcycles I keep the trans in first with the clutch disengaged. Never know when you may need emergency acceleration!

Even if you are third in line at a light? And if first…you are going to make an emergency acceleration into traffic? That makes the wreck YOUR fault. I’ll save my throw out bearing an sit in neutral.
I doubt there is time to make a plan and execute in most true “emergencies”. If there is time? The fraction of a second to grab a gear might be enough.