r_vangieson

Alright I have been searching the forums, and I haven't seen any answer to this question. I often coast long distances .5 miles- 1.5 miles and I shift my AT into neutral. What I want to know is if it is destructive to my tranny? Now I do revmatch if I have to reengage 5th gear. My thinking is that revmatching should minimize any wear. Also I have seen people posting that you save no gas by coasting in neutral, but I don't think this is true. Reason being is that coasting at say 70 gets you 2500 rpms approximately. But shift into neutral and your down to idle revs approximately 800-1000 rpms. Now simple math to me says fewer revs per minute, less gas burned. Also with tranny disengaged less friction. Should be only axles since tranny is not engaged. Anybody with arguments to refute my hypothesis I welcome. I want to be sure I'm not ruining my tranny. Thanks

jlukja

I don't believe you are damaging anything by coasting in neutral instead of in gear. When coasting in gear you slow down a bit more because the engine is doing the braking. Engine braking by shifting into a lower gear won't burn any more gas (the injectors are shut off, the breaking is by backpressure only) but it will slow you down much more than just coasting in neutral. Be mindful that coasting down long hills in netural with a lot of accessories running (A/C, CD player, etc.) can drain the batter down quite quickly. Remember that the engine is only turning at idle speed and may not keep up the battery charge under high electric load conditions.

fuckleberry

so you have AUTOMATIC tranny ?
(reads like you talking about MT)

sauceman

True. Coasting in neutral will save you some gas for sure.

It also shouldn't do any damage to your tranny. At least it didn't on my AT Accord back then.

psteng19

In an auto?

I wouldn't. No particular reason or technical explanation. It just doesn't "feel" right.

peter_bigblock

I would never be driving a car coasting in neutral, MT or AT. Too many things can happen that require split-second throttle control. Really, you're going to save gasoline by rolling along in neutral? Are you going to save on your brake pads, too, by holding your hand out the window and flapping it forward before you stop?

sauceman

Well, I must say I've changed the original pads at 172,000km...

tsxflexer

Your not saving any gas coasting in neutral. Here is the reason why. When you coast in neutral air/fuel is fed into your engine to keep it at idle. When you stop accelerating when your in gear no fuel/air is fed into your engine because the engine is using the momentum of the transmission to move unless you go below 800RPMs. If you don't think this is true or correct go buy an Air/Fuel guage and see for yourself. When you idle in neutral the meter will fluctuate from lean to rich meaning that your ecu is feeding just enough fuel and air to keep you from stalling out. When your moving and you take you foot off the accelerator the guage will blank out meaing that your engine is not being fed any fuel. If your coasting down a hill for .5 - 1.5 miles your actually going to waste more fuel in neutral than in a higher gear.

karoberts

Someone I knew who was supposedly "a car guy" told me that you shouldn't be in neutral in an automatic over 35 MPH. His reasoning was that an auto isn't supposed to be in neutral while moving, it's not quite like disengaging a clutch, there are still things turning in an auto.

I have no idea if this is true, but automatic transmissions are more complicated, so I think the prudent thing to do is not risk your transmission and leave it in gear. If you want to drive in neutral, get a 6MT. My

BusyShifter

Surely you are not encouraging people to coast in neutral, right? Recalling you suggest people should be getting winter tires when there is snow for safety reasons.

Like Peter stated, I was always taught that it is unsafe to coast in neutral, MT or AT. I wonder how much gasoline one really saves by putting the car in neutral.

jkozlow3

Jesus. People are buying $30,000 cars and worrying about saving a few pennies by "coasting in neutral"????????

That sounds terribly unsafe. Like peter_bigblock pointed out, too many things can happen that require split second control.

I think this is the most ridiculous conversation I've seen to date.

TinkyWinky

If you really want to save gas, switch to narrower tires and fold your mirrors during highway driving.

blueglows

yea i read on the owners manual for my dads benz that coasting in neutral or just shifting into neutral while you are going over 20mph can damamge the engine "and will not be covered under the warrenty". When low on gas, my dad shifted in into neutral down a hill to save gas and as soon as it went into neutral the rpm shot up as if it was at WOT and went back down. This was pretty scary and i have no idea why it happened. I have done it in my car many times not to save gas but to rev the engine. For ex: pn the way home today i was doing like 40mph and was in a tunnel and saw a little honda civic next to me who kept reving at me... i droped it into neutral at 40mph and gave it a quick rev...( while you are moving you are allowed to go past the 5.5k rpm limit cl-s i dono why but when you are stoped it only lets you rev to 5.5k and when you are moving even just a little bit it lets you rev to about 6k rpm which is alot louder! and sexier to hear) then i waited for it to drop back down and shifted into D...everytime i do this i never feel any gear grinding or like the tranny is having trouble with it...its very smooth and if you didnt hear the engine you wouldnt think anything even happened...

swirlie

Narrower tires, yes. Folded mirrors, no.
You'd be better off taking the mirrors off completely and filling/smoothing out the holes left. With a folded mirror, you create bad lines and sharp edges, disrupting airflow just as much or more than the mirrors in their normal positions.

YOTH

I'm from the old school that one shouldn't put an AT in neutral for extended periods...myth? Maybe, but that's what I was told.

I'm a firm believer that acceleration/braking/steering is your only source of control of a moving 3000lb vehicle. To disable one of your controls to save a bit of gas could be seen as foolish & reckless.

STEELTOWN

Does not surprise me about the Benz, those guys can't seem to keep a car on the road lately, talk about reliability. Hell, they are probably looking for any excuse to deny a claim and save money. "Uh sir did you put the key in the ignition? Well sir that activity is not covered under warranty, we never intended you to drive it." You can insert BMW and VW in there too.

jlukja

Nooooooooooooo. Not the "Ultimate Driving Machine".

psteng19

Wow, unbelievable.
Please tell me you are kidding.

jackacc

Amen to that. Well I do think BMW is at the top of the list of these 3 (quality wise) but when you bring your car in for an oil change/tune up, it's like making a mortgage payment...

sauceman

Teeheeehee.

You tell me in which situations it would be unsafe to coast in neutral, because since the time I've been doing it (usually down hills on highways or coasting down to stops, etc...) I've never been in a situation where it was unsafe to do so. You don't need to throttle your way out of a "slowing down for a stop", nor do you need to do so for going down a hill. If it did, then it would be just as unsafe to drop the gas while going down those same inclines.

Just name me one situation where you need to throttle your way out of it while being in neutral. I am willing to discuss it.

BTW, even if that situatione were to ever happen, it takes no more than a "split second" to get back in gear and "throttle your way out". Think about it.

When you get off the throttle in gear, you are slowing down the car with compression. You are effectively doing a form of braking. Engine braking. By doing so, you are wasting inertia. Coasting in neutral will not only not waste that inertia, it will utilize it. And the distance you will cover in neutral will more than outmatch the tiny amount of gas you are using by idling.

Now, if these explanations don't convince, just check out my own fuel economy data (a few threads about this here and there) and if using neutral really does nothing, I dare anyone to match my results without coasting in neutral, on a 20 Litre gas tank. We'll see about it then.

Until then, I have achieved by far the best fuel economy numbers on any TSX. Nuff said.

sauceman

Yeah, I've been told this as well for our Smart. I don't know for what reason that would be exactly, since it is a 6-speed sequential gearbox.

Maybe it has to do with lubrication within the gearbox. But anyhow, the Smart already performs mind-boggling fuel-economy without having to use all thos little tricks.

As for the AT, I really couldn't say a definite yes or no. The fact that I've never had any problems for 585,000km may be an indicator, but definitely not fact establishing. I would have always thought that since the AT tranny is driven by a torque converter, the wear would be identical on the torque converter whether it was driven by the engine or by the transimition. Beyond this, I'm not too familiar with the internals of an AT gearbox, so I wouldn't risk myself by saying anything.

jlukja

I'm with sauceman on this. I've done it and never felt I was taking chances with safety while doing it.

The original poster asked if it was destructive to the tranny. A lot of posts here address the safety aspect, wrongly or rightly, but no one has put forth a convincing argument on whether or not this is destructive to the tranny.

DaveWhyman

I coast down hills all the time in my car, and have done it in other cars too, mind you most of them were MT. I wouldn't do it in a mid 90's Ford though, those AT's had a tendency engage real hard and blow up.

jkozlow3

Not terribly likely to happen....BUT, what if you're coasting in neutral on a semi-flat surface and something fell off the back of a truck in front of you and it was rolling toward you (a steel tube, a tire, etc)?

You'd probably be much better off accelerating out of the way rather than braking and letting the rolling object fly into your car.

Just a thought.

r_vangieson

with regards to safety and control as being reasons not to coast in neutral, I never coast unless there is a large gap (10-15 car lengths). Now as to the engine not using less fuel when idling, I don't see how an engine engaged can use less fuel than one not. Unless the pistons are not receiving fuel (which I doubt) then an engine turning 1500 fewer RPMs must use less fuel, right?

jlukja

Actually, the TSX engine can use no fuel under certain conditions. For instance, when engine braking, the fuel injectors are shut off. The only thing slowing you down is the back pressure of the air(without fuel) acting against the moving pistons.

But, as sauceman said, if you are coasting in gear then you are not using fuel but you will not coast nearly as far as you would have had you been coasting in neutral. You would then need to burn fuel to get to where you would have gotten to in neutral, and that is more fuel than you burn idling in neutral.

^^that made sense when I wrote it, hope it makes sense when someone reads it.

BusyShifter

Hey, I am not saying that you act irresponsibly for coasting downhills in neutral. I respect you for setting mutilple records on those unreal MPG numbers (what is it, 40+ mile per gallon?). Yet, I believe in general, it is unsafe to coast in neutral.

If a driver simply panicked or "forgot" he was in neutral and needed to accelerate to get away from trouble, or he/she "mis-shift" while trying to get back in gear, the "split second" could be very costly at highway speed. After all, "accident" is not something that we predict to happen, right? Sure, you can blame the problem on the driver instead of the gear. However, the act of putting the car in neutral increases the chance of an accident to happen.

I don't mind that you don't agree with it. Thousands and thousands drivers don't think talking on the cellular phone make them unsafe drivers on the road. They might claim 99% of the time, they pay as much attention to the traffic as not on cellular phone. However, that still means talking on the phone contributes to the 1% additional chance for them to get into trouble.

Now, imagine that you are the passenger in a car that the driver are on cellular phone and coasting in neutral.

Yup, I understand this is a thread regarding to "any damage on the transmission". I could not think of a reason that it would affect the transmission in any way mechanically, especially in automatic transmission. However, if the car suddenly become hydroplaned for whatever reason, would you rather to need spending the time finding the right gear, or just focusing on gaining controlof the vehicle?

To save gasoline, I would rather drive conservatively than forfeit the control of my car to neutral drive.

r_vangieson

So if i understand correctly, when I lift off the gas at say 70mph all four fuel injectors stop quirting, and I am essentially using no gas?

BusyShifter

In neutral, gear not engaged, engine turn to idle RPM. I guess there is still minimum amount of gasoline being consumed to keep engine running at idle, but no gasoline was used for the motion of the car -- it is like a run away train, the momentum keeps the object moving.

I am pullint this from you know where .

fuckleberry

you never confirmed whether you're talking about AT or MT

swirlie

Confirmed.

tsxflexer

Maybe when coasting down hills you should just put it in neutral and shut the car off. This way you use no gas, oil, and electricity. Your car will become more efficient than a Toyota Prius.

sleeper

interesting. i think we need a poll to see how many people drive an AT like a normal person would. you know, the basics: get in car, start up, put it in d, use pedals (w/one foot only ), put it in p, turn off, get out of car.

btw, i've seen people forget to put the car in drive at a light because they don't want to leave it in drive for 30 seconds. scary thinking about what those people would do when the car's moving. it just seems too many things can happen by accident when driving around in n. if you drive with little traffic in safe conditions, i don't think it's particularly unsafe. but hey, no one's gonna stop you either way.

peter_bigblock

I think, in the interest of saving as much on gasoline as possible, when going on trips where you don't anticipate heavy acceleration or hill climbing, you should remove two pistons and injectors as part of your pre-departure checklist. Turn off the dome light -- that electricity has to come from somewhere! Also, turn off the ignition and suck in your stomach while you're coasting down hills in neutral. And tell your wife to forget about that double cheeseburger. She's KILLING your mileage! Give her a carrot.

Pure Adrenaline

iTrader: (2)

Coasting in neutral is fine. The transmission is disengaged from the engine. But you will have no throttle control, which is a scary thought in my opinion.

However, it's the re-engagement part that is not fine. Those of you who said you "rev match"... What you're doing is effectively the same as standing still, revving the engine then throwing into drive. Automatic transmission has one main gear shaft from the engine, which has 5 (in the TSX) individual shafts attached to it. They are constantly in contact with one another, and they simply lock and unlock to engage and disengage each gear.

When you're coasting, then throwing into drive, the TCM first engages first gear, then realizes the speed is high enough for second, so it upshifts, then upshifts again, and so on until the proper gear is selected. It is definitely not good for the transmission. It is not like a manual transmission where you can select the gear on your own. Whatever gas money you save by doing this, you will pay A LOT more in possible transmission problems later on.

grasseater

i'm not sure how you've got your TSX set up but i know in mine i don't have to punch the gas in order to turn the wheel.

r_vangieson

I want to make sure I understand correctly. Even if I match revs I am still potentially doing damage? What about the fact that if I don't rev match there is a noticable shudder, but when I raise revs it is a smooth engagement. Am I just being fooled, and if the potential for damage exists why isn't neutral locked out to prevent an accidental engagement similar to reverse if the shock to the transmission is so bad?

sauceman

and

Thanks. Those are situations where effectively risks are increased.

When you recognise a dangerous situation, you try and get out of it. Same for neutral. If it looks like there could be a risk, I just don't do it.

It's like driving around on cruise control (which can be A LOT more dangerous than neutral coasting IMO, because you are consciously or unconsciously reducing your control AND attention on what's happenning around you... same as being on the cellphone). Is it safe to use it in semi snowy, semi slushy or even thoroughly wet conditions? Positively NO. (I learned the hard way about this younger, gave myself a hell of a scare) So I just don't use it in those conditions. Nevertheless, for the specific conditions of hydroplaning, at the speeds I drive to save up on gas, hydroplaning is very rarely an issue.

Recognise a danger and avoid it. Driving intelligently, using your head is worth a lot more than arbitrarily saying "you should never coast down in neutral because it's dangerous". In general it's not, but for those few situatins when it could become a risk factor, then just use your head and don't do it. I know I don't.

But I know sometimes when you look at people driving around you just that seems like a challenge (driving with your head).

sauceman

Appreciate your thought.

However, in case you choose to come back down from your ivory tower, you should know that not everyone here makes 20k/year on their car.

If I was to drive around carelessly, I would use as much as 25% more gas. If I was to buy all of my gas where I live (and not in Vt), I would pay another additionnal 25-30%. Multiply that by the 6500 litres of gas per year I need to travel my 90,000km at the average price of $0.80/L, and that means I saving anywhere between $4500 to $5500 (cdn) on my budget for gas.

And I haven't even started talking the tree-hugging talk.

sauceman

Probably because there could be situations where neutral could become a necessity, like if you ran out of gas.