In AT going from N -> D
 

Well my friend has an 02 TL-S and he always shifts into neutral for example while going downhill and then while still at about 35 mph, he shifts back to D. He says it saves gas, but I think it would burn the transmission, seeing as how it would the tranny to go from N to 1st gear while at 35 MPH. Is this necessarily bad? The furthest I go is shift into neutral to coast and then I make sure I'm at a full stop before I shift into D again.

Thanks

Very bad for the transmission. May not see the effects right away but you will eventually.

I rev match in N before I put it back into drive again.

I had the habit of putting AT into N at traffic light for years.
When I got TSX I decided to find out if this is bad thing to do.
The more "educated" consensus is that this is a bad thing to do - shifting btw N & D
Modern AT is designed so you don't have to touch the shifter.

KEn1997TL, there's no such thing as rev matching with an auto transmission, in part because the tranny picks the proper gear based on speed and conditions. You may be revving the engine before going back to drive, but that's about it; it doesn't accomplish anything. I'd say that adds more shock to the drivetrain than simply putting the gear selector back in to drive from neutral at at any given speed. Don't try to out thinks the engince computer.
blackjackman said it best:
"The more 'educated' consensus is that this is a bad thing to do - shifting btw N & D
Modern AT is designed so you don't have to touch the shifter."

Automatics are designed to be left in D until you need to put it in P. Also, it is hard on the brakes when you put it in N going downhill.

Maybe so. My TL is the first automatic I've had, I'm looking at getting a tranny swap from a Legend.

i dun get why there are the recent N->D posts. its an automatic its suppose to be left in the drive position.

Auto shift
 

The TL trans. is designed to automatically downshift on long,steep downhills to provide engine braking. Remember when your is in gear and coasting the throttle is already closed so putting the the car in N will save miniscule amounts of gas. Certainly never enough to pay for the additional brake wear.
As it was said so well before, don't try to out think the computer.

The car's towing instructions provide a clue here. The transmission can safely freewheel as long as you go from drive to neutral. If you put it in reverse first (such as shifting directly from park, through reverse -- without first putting it in drive) then you're setting yourself up for a disaster.

As for automatic downshifting, ATs include a variety of clutching mechanisms. If you simply let it coast in drive, the one-way clutches (think "ratchet") eliminate most of the engine braking effect. If you command it to a lower gear, however, you will get engine braking to the extent that the torque converter will transfer the load.

So, if you truly coast in neutral you will get better mileage than coasting in drive -- but if you want "real" downshifting you need to work the shifter.

I always shifted from D to N at red lights in my old Altima. I sold it to a friend who is now driving it with over 120k miles and it's still on it's first tranny - going strong.

If it does hurt the tranny, the effect is so minimal it's hardly worth mentioning.

Having said that - I'm not doing the red light shifting with my new remanned tranny. :)

Just leave it alone in D, that's what having an auto tranny means.

:agree: The torque converter in all auto trannies is what allows the car to come to a stop without the need for clutch pedal and without the need to shift to neutral, as with a stickshift. There's no reason to shift an automatic. And it's much better to use the brakes for slowing the car rather than the transmission. It's less expensive to replace brake parts than transmission parts. Sure ONE Altima went 120k miles, but why take the chance?

Are the replies that say it's hard on the brakes to use N on downhills assuming that you will be actually braking on the downhill? Or is there some special relationship here between brakes and transmission with which I'm unfamiliar?

I just finished a week of driving through mountainous terrain. There were several spots where I put it in N and coasted for miles. One stretch had to have lasted for at least ten miles. I originally tried leaving it in D, but the car would start to slow when I took my foot off the gas. In N it would maintain speed.

Is there really an issue with shifting from N to D while moving? If the SportShift can accomodate bad shifts by automatically matching engine speed before making the shift, it seems like shifting from N to D should be able to do the same thing. I know the tranny gave not a hint of complaint when I went from N to D at 75 MPH. It appeared to just slide into 5th and the RPMs moved from 500 to a bit over 2000.

As to the original question, unless those 35 MPH hills last for miles and miles, I can't imagine your friend is saving enough gas to make it worth even thinking about shifting to N. I only messed with it because I knew I had many miles of steady downhill.

QUOTE As for automatic downshifting, ATs include a variety of clutching mechanisms. If you simply let it coast in drive, the one-way clutches (think "ratchet") eliminate most of the engine braking effect. If you command it to a lower gear, however, you will get engine braking to the extent that the torque converter will transfer the load.[


Read the manual. It very specifically says the trans. is designed to sense and downshift on long steep downhills to provide engine braking. In this case it's not "don't try to out think the computer" it's more don't try to out think the engineer who designed the damn thing.

It seems like the tq converter unlocks around 30 or so when coming to a stop. I also shift into N when coming to a stop from over 40 mph and will coast as far as I can to the stop.
I believe I gain about 2 mpg when I shift to N like this. But just going down a hill I would not put it in to N. I usally only do it when I know I am going to stop.

Although there is no reason to do it it causes no harm. If you live in and area with a 20 mile down hill stretch it might improve your milage some. Longe live manual trannies! One thing that does improve milage significantly is turning off the engine at stoplights and non-moving traffic jams. In Germany the traffic signals go from red to yellow and then green to encourage turning off your engine at the light. In cities it cuts on noise pollution and fuel consumption. I always wonder why simple solutions that other countries have adopted forever can never be put to work here?? I guess it comes back to the usual American jingoism that if we didn't come up with it ourselves then it just wrong!

vtechbrain - wouldn't that wear out your starter?

I dont see that as a problem (at least for hondas). The auto start feature is "the new thing" for all hybrid cars. The only difference in the hybrids is that it doesnt entail turning the key.

http://www.startribune.com/stories/432/3397313.html

If you are in drive at a stop for 5 minutes (like at a railroad crossing) the temps in the tranny oil go way up from the action of the stator. The best thing to do is to shut the engine off - it amazes me when I am in a long wait traffic situation, and there are 100's of cars in Drive, with their brakke lights on, and that troque converter whipping the fluid into a frenzy of heat, noxious fumes making me dizzy, and the wasted fuel driving 3 tailights!!

In some states, being at a stoplight without your foot on the brake is illegal, though. I have never heard of anyone being nailed for it, but it is possible. Of course, the one time I got rear-ended, i heard the car screeching behind me, and took my foot off the pedal to reduce the impact energy exchange. It still crushed a vertibra in my neck (ouch), and forced me to see my NSX (grrr!).

I've been told it is illegal in many states to drive with the car in neutral. Essentually, you have no ability to accelerate out of a problem, you may cook the brakes on very steep hills, and your suspension is unloaded (less stable).

The other thing is cars use as little fuel as possible on decel (leaned out to improve fuel economy, yet rich enough keep the cat lit), so idling a car down a hill could use more fuel than just coasting in D. Fuel injected cars used to cut off fuel completely on decel (80's VW's & 92 Civic HX) and the engine temperature would go cold down long grades, but modern emission standards don't allow the cat to go out.

That's not what *I* read in the manual. The manual gives the *maximum* speeds at which the transmission will automatically downshift while traveling on level ground or downhill. This is not about engine braking; it's about gearing.

For example, if you are coasting downhill and decelerating, the transmission will shift from 4th to 3rd at or below 18mph. As anyone who's driven the car will know, shifting from 4th to 3rd at 18mph does not provide perceptible engine braking. This downshift is intended to make useful engine power available for when you feed in the gas after slowing.

Similarly, the uphill speeds (4th to 3rd below 41mph), reflect the need for more torque to maintain a given speed on a hill.

If the transmission were downshifting for braking, then there would be speeds *above which* the transmission would automatically downshift while coasting. In fact, the only way to get the 5at into a lower gear while picking up speed in a downhill coast is to manually downshift. And again, manually downshifting creates more engine braking than simply coasting, which uses one-way clutches to reduce drag.

umm, i have coasted at about 60, shifted into neutral to rev at someone, and shifted it back into auto.
It never goes through first gear. The auto tranny shifts into 3rd automatically.

There are too many variables to make any definite pronouncement on this. If you're going down a hill where coasting in D allows you to maintain your desired speed, then coasting in N would force you to at least periodically tap the brakes to keep from accelerating past your desired speed (and this would result in wear on the brakes and possibly screwed up traffic due to reaction to your hitting the brakes). Conversely, if coasting in N allows you to maintain your desired speed down a hill without touching the brakes, then engine/tranny drag in D would force you to step on the throttle to maintain the same speed. And what effect any of this would have on overall pollution is way beyond me. My gut says that engine at idle means less gas consumed means less pollution, but I also know that gut instincts are not always correct with this kind of stuff.

I was actually thinking about posting a thread about this same thing. I have done this w/ my Mitsu Galant since I bought it new in 03. It's got 128,000 miles and no problems w/ Tranny. Shifts like new. I started doing this w/ my Acura the past few weeks and have noticed a HUGE improvement in my MPG. I went from about 26mpg on my trip to work to sometimes over 36 mpg on my MID. And it's a correct reading since I get more miles before filling up at the pump.

Do our cars have DFCO (deceleration fuel cutoff)? I think it's present on most new cars... cuts off fuel when decelerating in gear. This would yield a higher true mpg. I wonder if the MID shows an increase because it uses an algorithm based on RPM, rather than true fuel consumption. Not an expert, but just some thoughts =).

Oh contrare':
Acura as well as many other modern machines are indeed rev matching. The new 370Z comes to mind. Kindly reference:
http://www.hondanews.com/categories/735/releases/3747

I believe Ken is jesting, as his practice would be very hard on internals.

Only a matter of time before SouthernBoy jumps all over this thread :toocool:

'07 TL-S CBP/TAUPE 5 A/T
FUJITA F5
PROGRESS RSB
P2R TBS w/gaskets
Braille battery
V1 on the lookout

In nearly all modern machines today, including Acura, there is no fuel flow if the throttle is shut.

This has come about mainly due to emission controls.

Hence, putting a modern transmission into neutral won't make any difference in fuel mileage.

As some people have complained about on this forum, the TL actually slows itself down substantially with the grade logic built into the 5 A/T

Helps on making the brakes last a little longer too :thumbsup:

N is one of the most useless gear position in the morden AT. i use N gear very rarely.

dont use N for downhill cuz it dangerous and bad to the tranny itself.

O.k... when I'm driving.. if I'm at the apex of a hill.. and it's a LONG way downhill, if on the downhill portion I pop it into neutral and coast, I DO save on fuel mileage.

1. Lower RPMs. I'm going on the understanding that an engine uses more gasoline to get the engine revving higher.
2. Not being slowed down by tranny. We all know that the Tranny is made to slow you down as you let go of the gas.. no matter what gear you are on.
3. Gravity may even cause you to accelerate. Because you are coasting downhill, you may actually even accelerate due to gravity pulling your car down the hill. (gaining more momentum while using very little engine help)

I have been doing this on my 03 V6 Galant since I bought it new (it had 1 mile on it when I test drove it and decided I wanted it). I have 121,000 miles on the Galant and she still shifts like a new car. I do tranny fluid changes every 30,000 - 50,000 miles on all my cars though. On my Galant I can tell you that driving in this fashion gives me about an extra 80 miles on a tankful. 300miles vs. about 380-400 miles if I drive that way. An extra 80-100 miles on a tankful is enough proof for me that it DOES save $$. I have only had the TL for a few months.. and because I never really fill it up (I have used Innacurate's suggestions of only keeping 2-3 days worth of fuel in the gas tank to avoid the extra weight), I haven't really gotten to gauge the fuel savings accurately.
I would think that an 03 Galant V6 is considered "a modern machine"... just my :2cents:

Not sure if I get the logic here.. how is going downhil in neutral bad for the tranny? Tranny is disengaged and not working when in neutral... No torque is getting to the wheels and the car is being moved by it's momentum and pure gravity.

Do you mean when shifting back from Neutral to "D"?? but I find that if I shift from N to D and I time it right (dependent on the speed and what gear will grab if I shift from N to D... this takes some time to learn your shift points on your car) it can shift into gear very smoothly. No jerking... you barely feel it actually.

Switching to neutral when coasting in an automatic is absolutely pointless, as when engaging drive, you are pushing your tranny and engine too hard.. and I don't care if you think you are rev matching... you are not as good as the tranny.

I only use Neutral when in reverse, as I'm done backing up, I'll throw it into neutral, and glide to a complete stop, and then throw it into drive.

I think some people are seeing increased mpg because they want to see it. Every modern car has deceleration fuel cut. My old '84 Buick had it. Sometimes there is a slight time delay programmed in. Usually rpms have to be a few hundred above idle for fuel to be cut.

Going down a long hill as stated above with the trans in gear uses 0 fuel. The engine is spinning but the injectors are off. Going down the same hill in neutral uses the same amout of fuel as idle.

Going from neutral to drive at high speeds is not the best thing to do but it isn't particularly hard on the trans either. It will go into whatever gear it's supposed to be in. If you go from neutral to drive at 65mph more than likely it's going straight into 5th gear.

The only time neutral willl save fuel is at a stop light. The torque convertor still offers some load (and corresponding trans heat) at idle in gear. Putting it in neutral will take this load off.

As for Acura's "grade logic", I suspect this was marketing's way of eeking a few extra mpg out of the car. Package it as a way of slowing the car on a grade or coming to a stop, and saving the brakes. What it's really doing is keeping the rpms up and the engine in fuel cut for a longer period of time.

So if I understood you right, I can "technically and theoretically" drive down a steep slope downhill forever without using any fuel while maintaining 55 MPH. So theoretically I can go down a 1000 mile descent with a full tank of gas, and when I get to the bottom of the 1000 mile mountain I will have the same amount of gas left in the tank.. (a full tank). hmmmmm....

If the throttle is shut, there is no fuel usage.

Make no difference what the rpm is.

The modern car adjusts vacuum, etc. internally, so there is no affect on the throttle opening.

I'm not critical of your '03, but it is a far cry from the newer machines, especially when it comes to emission/computer controls. They evolve every year.

So, to take your theoretical run to task:

If you put your car in neutral, and take 1000 mile descent vs. leaving the car in gear, you will use less fuel only because you traveled at a higher rate of speed (no transmission drag), and arrived at your destination sooner.
Less engine run time= less gas.

Yep. As long as the rpms are above the threshold (1,300rpm I believe), the injectors are off and you're using nothing.

Manufacturers set a threshold rpm and if you're under that rpm the injectors won't shut off. It's usually just above idle speed.

However, that last statement isn't exactly true. If you're using 0 fuel, it doesn't matter how long the trip is, you're still using no fuel.

hmm... so if I go down this hill.. maintain 55mph and keep my rpms above 1.3k I don't use gas... even if I'm in 2nd gear and @3k rpms?

What is keeping the engine running? Battery? why if I'm idle do I still feel exhaust? Isn't exhaust a product of the cumbustion of fuel + air?

BTW.. this has been a great informative thread for me since I know I save gas on the Galant, but was unsure of the TL. Don't want to tax my tranny any more than I have to due to the known tranny issues w/ our cars.

The engine still spins. It's mechanically linked to the wheels.. However no fuel is being injected. If it's spinning it's still moving air, it's just doing it with no fuel.

Sitting still at idle it's using fuel. Coasting at 55 with the wheels and gravity spinning the engine it's using no fuel.

But you are not using 0 fuel.

As long as the engine is running, you are using fuel. If you turned the engine off, then you would be accurate. If the engine runs 10 minutes, it uses less fuel than if it ran 20 minutes, even at idle.