Benificial for an auto tranny??

[901Memphis]

This has come up many times. You are causing the fluid to heat in drive when stopped but the system should be designed to cool the fluid. The best thing would be to have an oversized transmission cooler then you have zero issues with leaving in drive at stops.

The bigger issue is the inability to instantly drive off if an emergency arises... Maybe seeing something in your mirror about to hit you? Those extra few seconds could cost you.

Maybe someone coming up to grand theft auto you? The possibilities are really endless.

Plus the clutches wear when engaged and disengaged so it all around a better practice to leave it in drive unless you suspect the fluid is actually too hot. A synthetic fluid with better oxidation stability can also help mitigate that as mineral based fluids will oxidize faster at the elevated temperatures... Most of us BITOG guys change our transmission fluid plenty to counteract this.

The only time I neutral is for trains.

 

[Kawiguy454]

If engine is idling and you put it in gaer and the car starts to move the tq converter is pulling the car. Hitting the brake does not make the dragging stop but more gas has to be fed in to keep the rpm's from dropping.

I will concede that new cars this effect is much less but it still works the same way. in gear vs neutral still takes more fuel and makes more heat.

 

[demarpaint]

Originally Posted By: 901Memphis
This has come up many times. You are causing the fluid to heat in drive when stopped but the system should be designed to cool the fluid. The best thing would be to have an oversized transmission cooler then you have zero issues with leaving in drive at stops.

The bigger issue is the inability to instantly drive off if an emergency arises... Maybe seeing something in your mirror about to hit you? Those extra few seconds could cost you.

Maybe someone coming up to grand theft auto you? The possibilities are really endless.

Plus the clutches wear when engaged and disengaged so it all around a better practice to leave it in drive unless you suspect the fluid is actually too hot. A synthetic fluid with better oxidation stability can also help mitigate that as mineral based fluids will oxidize faster at the elevated temperatures... Most of us BITOG guys change our transmission fluid plenty to counteract this.

The only time I neutral is for trains.


Well put.

 

[Kawiguy454]

The OP is in florida ...In 100 degree Miami heat the stop lights were at least 2 minutes or longer when I lived there. and where i live now in Arizona on a 115 degree day heat is the enemy.

What rational person would think that clutch pack wear from a neutral to drive at idle with cool fluid compares to the 1st second shift under power with fluid that is elevated 50-100 degrees over normal.

My wife's G8 has on dash engineering mode... I can watch the trans temp rise real-time sitting at a light. My last comment on this is to make your own decision.

 

[CT8]

Bumping the tranny into neutral at the lights causes the forward clutch to engage/disengage 1 extra time. In theory that is more wear. Most of the heat comes from the torque converter.

 

[CT8]

Originally Posted By: zach1900
In drive at a stop isn't the transmission technically slipping the whole time?
Lets hope the trans is not [slipping].

 

[Kawiguy454]

A word problem:
...2 identical cars stopped at a 2 minute stop light in 100 degree heat. Car A switches to neutral and car B does not. When the light changes green car A puts in drive and both cars take off. When both cars shift thru the remaining gears car 2 has elevated fluid temps. Which car will have more clutch pack wear?

Also keep in mind that some of the friction clutches (multiple) are not plates but bands (like 2nd) that clamp down on other spinning components and don't have nearly the same wear potential as plate type.

I guess the word problem fails if the dope in car A accidentally puts it in reverse and backs up into a cop car.

 

[Quattro Pete]

Originally Posted By: badtlc
Originally Posted By: NHGUY
I'm surprised by now they haven't come up with a computer scenario for that...sit at a light for more than 30 seconds,and the computer will automatically shift the trans to neutral,step off the brake and it re engages the transmission to the gear range chosen on the shifter.


it already goes beyond that. many modern cars turn the engine off at stoplights.

Exactly. And for this to work, you do need to have your foot on the brake pedal. Taking the foot off brings the engine back to life.

 

[440Magnum]

Originally Posted By: Kawiguy454
It never ceases to amaze me that a certain percentage of responses always involve how badly things will go wrong when I knowingly take an action then somehow forget where I'm at and what I'm doing resulting in a catastrophic chain of events. Must be some of you had a nanny growing up to take care of your fails before they happened.

Disclaimer: If you on meds or just stoopid ...don't try this at home it could lead to an epic fail.

Sitting at a light stopped the 1st gear clutch pack is engaged fully and the torque converter is slipping. The fluid temperature rises probably 50 degrees in a minute. If it is stop and go traffic the high temperature will soak in and never go down to normal cruising temp until after you're cruising again. The slipping tq converter is why we put transmission coolers on towing vehicles and race cars.


Have you actually watched a transmission temperature gauge to verify that "50 degrees in a minute" claim on a modern vehicle? I've watched the trans temp on my wife's Grand Cherokee (I tend to leave the EVIC display on either trans temp or oil pressure when I drive it), and it sometimes actually DROPS while idling at a light... in gear. Especially if the driving prior to that has been a lot of low-speed crawling with a lot of shifts. It may be true that my '69 Torqueflites heat up at stoplights- in fact I'm sure they probably do what with 750-800 RPM idling 440 big-blocks in front of them... and yes I tend to slip them into neutral because of that fact. But that's not what most people drive today, and I don't bother doing that to newer cars.

Yes, the torque convertor is the biggest source of heat when towing... but its when its actually accelerating through the gears (before lockup) that it generates the heat, not idling at <600 RPM at a traffic light. Torque convertor coupling is very non-linear, and the "slippage" generates a lot less heat at 500 RPM input than it does at 800 or 1000 RPM input. Most newer cars will barely "creep" at idle when you lift off the brake, whereas older ones require a firm foot on the brake to hold them still.

 

[demarpaint]

Originally Posted By: 440Magnum
Originally Posted By: Kawiguy454
It never ceases to amaze me that a certain percentage of responses always involve how badly things will go wrong when I knowingly take an action then somehow forget where I'm at and what I'm doing resulting in a catastrophic chain of events. Must be some of you had a nanny growing up to take care of your fails before they happened.

Disclaimer: If you on meds or just stoopid ...don't try this at home it could lead to an epic fail.

Sitting at a light stopped the 1st gear clutch pack is engaged fully and the torque converter is slipping. The fluid temperature rises probably 50 degrees in a minute. If it is stop and go traffic the high temperature will soak in and never go down to normal cruising temp until after you're cruising again. The slipping tq converter is why we put transmission coolers on towing vehicles and race cars.


Have you actually watched a transmission temperature gauge to verify that "50 degrees in a minute" claim on a modern vehicle? I've watched the trans temp on my wife's Grand Cherokee (I tend to leave the EVIC display on either trans temp or oil pressure when I drive it), and it sometimes actually DROPS while idling at a light... in gear.


The few times I had the opportunity to monitor transmission temps my observations were similar to yours. Both vehicles coincidentally were Jeep GC's, one was a friend's the other a recent test drive.

 

[440Magnum]

Originally Posted By: Kawiguy454

What rational person would think that clutch pack wear from a neutral to drive at idle with cool fluid compares to the 1st second shift under power with fluid that is elevated 50-100 degrees over normal.


OK, this is very dependent on the transmission design, but I can tell you that on some transmissions, the clutch that is engaged during ALL forward gears is made with materials sized and selected for many fewer cycles than the clutches and bands that are made to engage every time the transmission cycles up through the forward gears. Bumping in and out of neutral cycles a clutch pack that never gets cycled any other time in those designs.

In short- one answer doesn't fit all, and that pretty much applies to the whole discussion. Most vehicles with adequate transmission fluid cooling certainly don't benefit from neutral at lights... and some may even suffer a bit. But there are probably a few (especially older ones) out there that might benefit just a little bit.

 

[JFK]

How hard is it to not be mindless when operating a vehicle? Some how I manage to keep track of 5-6 forward gears in my POV all the time. I even use them to adjust my speed when cornering with out conscious thought. If I am driving a tractor trailer I have even more gears to keep track of.

Seriously if working an automatic between drive and neutral is too much for someone to keep track off give up now!!! LOL

Most fwd cars with manual transmissions use shift cables. I have yet to wear one out. The only company I know that routinely has car's under warranty wearing out shift cables are GM vehicles with automatics. If your logic worked then these would last forever.

 

[01rangerxl]

Originally Posted By: JFK

Most fwd cars with manual transmissions use shift cables. I have yet to wear one out. The only company I know that routinely has car's under warranty wearing out shift cables are GM vehicles with automatics. If your logic worked then these would last forever.


Not the same part. The manual shift cables I have handled have all been substantially heavier and larger than a run of the mill AT shift cable, because they are meant to be in use almost constantly. Totally different applications.

And it's usually not even the cable itself that goes bad, it's non-replaceable bushings at the ends (well, they are replaceable...in a cable assembly).

 

[philipp10]

Originally Posted By: Kawiguy454
It never ceases to amaze me that a certain percentage of responses always involve how badly things will go wrong when I knowingly take an action then somehow forget where I'm at and what I'm doing resulting in a catastrophic chain of events. Must be some of you had a nanny growing up to take care of your fails before they happened.

Disclaimer: If you on meds or just stoopid ...don't try this at home it could lead to an epic fail.

Sitting at a light stopped the 1st gear clutch pack is engaged fully and the torque converter is slipping. The fluid temperature rises probably 50 degrees in a minute. If it is stop and go traffic the high temperature will soak in and never go down to normal cruising temp until after you're cruising again. The slipping tq converter is why we put transmission coolers on towing vehicles and race cars.


The fluid does NOT go up 50 degrees in a minute....the cooling system will take care of that. I don't see it mattering much either way but going in and out of gear does cause some wear, but very little.

 

[philipp10]

Originally Posted By: Kawiguy454
The OP is in florida ...In 100 degree Miami heat the stop lights were at least 2 minutes or longer when I lived there. and where i live now in Arizona on a 115 degree day heat is the enemy.

What rational person would think that clutch pack wear from a neutral to drive at idle with cool fluid compares to the 1st second shift under power with fluid that is elevated 50-100 degrees over normal.

My wife's G8 has on dash engineering mode... I can watch the trans temp rise real-time sitting at a light. My last comment on this is to make your own decision.


The tranny cooling system is designed for the worst possible environment and the worst possible heat inputs. I highly doubt that is occuring at a stop light. Get real here.

 

[Stregone]

According to torque my car uses slightly less gas in gal/hr when stopped in neutral compared to drive. We're talking about ~.05 g/hr less.

 

[super20dan]

amcco recommends going to neutral if sitting in drive for over 1 min .says so in the papers you get after a rebuild

 

[MetalSlug]

Its automatic, let it do what it do.

 

[Nate1979]

Apparently those stupid auto engineers forgot to read this thread. Imagine how silly they would feel if you told them how they could easily program this into the transmission programming. LOL.

 

[hattaresguy]

Originally Posted By: NHGUY
I'm surprised by now they haven't come up with a computer scenario for that...sit at a light for more than 30 seconds,and the computer will automatically shift the trans to neutral,step off the brake and it re engages the transmission to the gear range chosen on the shifter.


My truck has a hill thing where the brakes grab if your stopped on a hill.

The entire shifting out of gear when in park is an out of place discussion to have about modern vehicles.

Shift cable? My transmission has a wire going to it....