Neutral to drive?

[mhmitszach]

Would putting my car in neutral down a hill and then back into drive have any ill effects on my transmission?

[VetteOwner]

no just dont slip it into reverse or park. its called an automatic for a reason.

[kamesama980]

as has been covered many times, it's fine. just don't do it at 90mph so the tranny has to rev the engine from idle to 4k rpm. basically, if you'll end up over about 2k rpm tap the gas a little to bring the revs up before shifting to neutral. this will eliminate any possible wear.

As with any component make sure you change the fluid periodically!!! not changing fluid is the #2 killer of transmissions.

[8307c4]

If you're going to do this also turn the engine off, otherwise you won't see much of an increase anyhow. I would make sure the foot is off the gas, and I speak from experience when I say you will hit Reverse at least once...

[Rick Rae]

If you're going to do this also turn the engine off...
Consider adding a safety warning or disclaimer when you're talking about an automatic transmission.

...otherwise you won't see much of an increase anyhow.
Absolutely incorrect. The most savings come from the neutral glide -- killing the engine is incremental.

If you don't believe that, do the math for yourself. Assume for the sake of argument that an engine burns 0.3GPH at idle. If a driver can manage to neutral glide 25% of the time (and I'd say that's optimistic), 0.075 gallons per hour is the maximum additional fuel savings.

I believe in incremental savings -- a percent here, a half percent there adds up. I'm only saying that leaving the engine on does not make the technique worthless.

...I speak from experience when I say you will hit Reverse at least once...
... unless A) your vehicle has a lockout (my VW won't go into reverse if the brake pedal isn't depressed) or B) you pay attention to what you're doing. ;)

Rick

P.S. As long as I'm mentioning disclaimers, I should point out that driving in neutral is technically illegal in a lot of places. Check your applicable laws and make informed decisions.

[MarvHein]

I would say any tranny dangers and savings may also depend on the fuel cutout and transmission logic of your particular vehicle. I'm lucky two of my three cars have onboard computers to help me weight the risk vs. the reward.

My 2000 Jaguar S-Type shows no instant mpg computer readout improvement shifting into neutral while coasting down a hill and bangs around a bit returning to drive. This is one I won't coast in neutral since there is no reward for doing so and there appears to be some damage risk.

But I saw dramatic jumps in instant mpg on the computer (99 mpg vs. 45 mpg) with my wife's GMC Yukon XL. Overall, the Yukon XL increased nearly 20% to about 15.3 mpg in its first full week of city driving with coasting in neutral.

Shifting in-and-out of drive is very intuitive if you're used to driving a manual transmission. Returning to drive from neutral usually happens when stopped at a stop light or turning a corner at very low speeds. There is no noticeable bumping or clunking from the tranny, unlike when I use the cruise control, where it often bangs quite dramatically coming out of coast on the highway. Whatever I'm doing to the transmission sure seems safer than what the designers hopefully accounted for in their cruise control system. :)


http://www.gassavers.org/gaslog/sig.php?id=1079 (http://www.gassavers.org/garage/view/1079)

[Hateful]

I coast in neutral whenever I can and it does help the FE ( per ScanGauge). I also rev the engine a little and shift back into drive as the RPM's decline; it feels smoother that way to me.
And I have shifted to reverse but was going really slow and only for a brief moment.I don't think it damaged anything.

[8307c4]

If you don't believe that, do the math for yourself. Assume for the sake of argument that an engine burns 0.3GPH at idle. If a driver can manage to neutral glide 25% of the time (and I'd say that's optimistic), 0.075 gallons per hour is the maximum additional fuel savings.

I believe in incremental savings -- a percent here, a half percent there adds up. I'm only saying that leaving the engine on does not make the technique worthless.


... unless A) your vehicle has a lockout (my VW won't go into reverse if the brake pedal isn't depressed) or B) you pay attention to what you're doing. ;)


P.S. As long as I'm mentioning disclaimers, I should point out that driving in neutral is technically illegal in a lot of places. Check your applicable laws and make informed decisions.

No automatic should ever be shifted, if you want disclaimers.

And most fuel engines burn 1/4 tank every 3 hours of idling, that would be a lot closer to a gallon an hour, but for the sake of argument I measure fuel consumption in ounces and I believe that's 2 ounces per minute but really all you're doing is lengthening the time off interval. Only time gliding is profitable is over stretches that last more than a few seconds, I wouldn't bother shifting for less than a 20-30 second glide anyhow, constant gas is as likely to maintain the economy.

You gain a small percent by gliding in neutral because your transmission is no longer creating drag, but the other half of the equation comes from turning the engine off. If small percents matter that much, then turning the engine off certainly should.

Yes, you should let the engine rpm's rest at idle before turning it off.
Better yet don't do it unless coasting to a stop.

Because I am telling you sooner or later you will hit R when coming out of drive.
I didn't say it would happen a lot, it might not happen the first 4-500 times, but sooner or later it will. No matter how careful you are, and if it happens once it happens twice, thou I am sure your perfect driving or your lock out never malfunction.

[kamesama980]

^shouldn't make all-inclusive statements. a metro takes a LOT less fuel to idle than a v8 yukon. most transmissions don't mind it at all if you change the fluid even 200% service interval. some do tho, so do your research. the auto that came in my car has had people do hundreds of redline N-D shifts to do burnouts in cars with over 150k and never missed a beat. I've heard certain manual subaru trannies shatter like glass when you launch in them.

in any auto trans, as stated above and elsewhere, if the manual says you can flat tow it, OK. otherwise you'll fry the transmission in very short order with the engine off.

[landspeed]

Jaguar S Types have WEAK auto gearboxes, don't try it again :) One of my friends had this car, and drove it normally, and the gearbox died at 60,000 miles. Also look on Carsurvey.org :)
My 2000 Jaguar S-Type shows no instant mpg computer readout improvement shifting into neutral while coasting down a hill and bangs around a bit returning to drive. This is one I won't coast in neutral since there is no reward for doing so and there appears to be some damage risk.


Also, in my current car (Bluey II), I get about 120MPG coasting at 40mph (therefore 0.3GPH ish), and almost 200MPG at 62mph.

Going into neutral means that the engine revs *drop* so that, although the injectors are injecting the same amount of fuel per cycle, you get less cycles per second, therefore less fuel is used.

Using neutral has allowed me to significantly increase my economy on short journeys (note that my journeys are getting shorter as I become more efficient at planning routes, timings, as I get used to this country, and get to know the area).

Engine-on neutral coasting is even worth it at 20mph in my car :)

[yi5hedr3]

Check with a ScangaugeII. You may have "fuel-cutoff" in which case you will burn more gas coasting in neutral vs in gear!! :)

[GeneW]

Would putting my car in neutral down a hill and then back into drive have any ill effects on my transmission?

Some automatic transmissions use the engine to run the pump. If you shut off t the engine you will damage the transmission from lack of cooling and lack of lubrication.

Gene

[kamesama980]

Some automatic transmissions use the engine to run the pump. If you shut off t the engine you will damage the transmission from lack of cooling and lack of lubrication.

Gene

all do unless you've discovered one with an electric pump. otherwise you won't get line pressure to push the clutches and plates together to start moving. Some transmissions just have an auxiliary unit on the putput shaft, splash/dip lube system, or something to keep them from burning up while being flat towed.

[geoff5093]

Efficiency wise, I just did a test with my new ScanGuage on my 2007 Camry, and when I was coasting down a hill at around 40MPH, it said I was using around 0.40-0.60GPH in drive, however when I put it in neutral is went down to about 0.25-0.35GPH. And of course the RPM's dropped from around 1200-1500 in D, down to about 600-750 in N.

[gto78]

I've tried something similar to this test in my 98 explorer. Everyday while driving to work I take my foot off the gas at the same place before my "Exit" ramp of the turnpike. I always coast from 70mph down to about 35 mph which happens in the middle of the exit ramp left turn/overpass. Then I finally step on the gas again to maintain 35mph until I reach the tollbooth. This is about a 1/3 mile distance.

When I try the same thing except put the truck in neutral I can coast the entire distance without having to step on the gas, in fact I have to slow down at the toll booth because I'm still going too fast. I basically get double the coast time in neutral. I realized from this experiment that the aerodynamic drag of my explorer wasn't nearly as bad as I thought, especially below 55 mph.

[Bruce]

no just dont slip it into reverse or park. its called an automatic for a reason.

Don't push the shift lock button (or pull forward on a column shift) when shifting between Neutral and Drive. This will prevent accidental shifts into Park, Reverse or the Low range. Just push the shifter back and forth.

Better yet, spend some time playing with the shift lock button and lever positions while the car is parked with the engine off to understand how it works. You should only need to depress the shift lock button to shift out of Park or to shift into Reverse, Park or the Low gears.

Going from Reverse to Drive only requires pushing the shifter back without using the shift lock button; Low to Drive is just pushing the shifter forward (to Neutral), then back (to Drive). You can also go from Reverse to Neutral using the opposite motion.

Knowing how the shift lock button works can save your butt when you're trying to panic stop on ice, because you need to have it in Neutral for the shortest stopping distance.

[RoadWarrior]

Jaguar S Types quite likely have the Ford EEC in, this is known to have injector cutout at speeds down to 1800 RPM (Might depend on application and torque convertor stall) then it adds fuel again to keep the motor running. Therefore if you coast in neutral in an EEC car down to a point where it needs 1800rpm or perhaps a little less to pick up again, you're probably using more gas than coasting in gear. Coasting down to a standstill, you might even be better off dropping gears manually rather than neutral coasting, keep it over about 1800. On roads that aren't in the middle of nowhere, you can't generally get away with a full coast down in neutral without severely pissing everyone off anyway, off-ramp coastdowns in gear and toward red lights doesn't seem to annoy people too much though.

By the way, many Ford transmissions DO NOT have a standard service interval specified for the transmission, this is why they die. Do maintenance per the severe service schedule and they live a lot longer (Basically just change the fluid every 30K or so) expecting trannies to go a lifetime on one fill is a bit optimistic IMO.

[k8crd]

Check with a ScangaugeII. You may have "fuel-cutoff" in which case you will burn more gas coasting in neutral vs in gear!! :)

Can you check with a Scan-gauge II if your vehicle has fuel cutoff?

If yes, what is the procedure?

Paul

[Minger]

the mpg guage will read 9999 if you have cutoff.

[popimp]

Consider adding a safety warning or disclaimer when you're talking about an automatic transmission.


Absolutely incorrect. The most savings come from the neutral glide -- killing the engine is incremental.

If you don't believe that, do the math for yourself. Assume for the sake of argument that an engine burns 0.3GPH at idle. If a driver can manage to neutral glide 25% of the time (and I'd say that's optimistic), 0.075 gallons per hour is the maximum additional fuel savings.

I believe in incremental savings -- a percent here, a half percent there adds up. I'm only saying that leaving the engine on does not make the technique worthless.


... unless A) your vehicle has a lockout (my VW won't go into reverse if the brake pedal isn't depressed) or B) you pay attention to what you're doing. ;)

Rick

P.S. As long as I'm mentioning disclaimers, I should point out that driving in neutral is technically illegal in a lot of places. Check your applicable laws and make informed decisions.


I'll have to disagree. I moved from Mississippi to Califronia back in October. Doing Neutral glides on the highway for 350 miles each day. The Scan Gauge 2 was convinced that I was getting 30 MPG. When I filled up I got 26 the first day and 24 the next. The point is don't take the Scan Gauge's word as gospel. The true numbers are in the fill up.

[Rick Rae]

I'll have to disagree.
You'll have to disagree with... what, precisely?

The point is don't take the Scan Gauge's word as gospel. The true numbers are in the fill up.
Scan Gauge wasn't mentioned at all in that message. And I agree that actual consumption is what matters.

Rick

[popimp]

You'll have to disagree with... what, precisely?


Scan Gauge wasn't mentioned at all in that message. And I agree that actual consumption is what matters.

Rick

Disagree that most of the savings are from the Neutral glide. Although each vehicle will yield different results.

[Rick Rae]

Disagree that most of the savings are from the Neutral glide. Although each vehicle will yield different results.
Thanks for the clarification. Your post seemed focused on the inaccuracy of the numbers you got from your Scan Gauge, so I wasn't sure what you were getting at.

Feel free to post your EOC figures to contrast with the neutral coasts. Unfortunately, driving an automatic as I am, I can't safely explore that area.

Also, don't hesitate to run the numbers using your actual fuel consumption and achievable coast percentages and post your results. What I gave was an example, and while I think it's a realistic (if optimistic) one, it'd be nice to see some real-world figures.

Rick

[Scott_in_Tulsa]

I just finished my first tank that included as much neutral coasting time as possible. This of course was with the engine running. I did manage to squeeze out 35 mpg and probably only did a neutral coast over 10% of the mileage driven.

I don't have a Scan guage or anything to help me monitor this performance other than the stock RPM gauge and keeping a keen ear to the sound of the engine. I have found that I can drop my RPMs from 2000 RPM in drive with my foot completely off the gas to about 800 - 1000 RPM in a running neutral coast.

I think this can be a huge benefit depending on the vehicle weight. The last two days I have been driving in rain and snow and added 100 lbs to my trunk for a little extra stability. The weight of course negatively affects my overall fuel mileage but I have noticed a positive in my coasting distance with the added weight. Not sure, but it may help balance out the fuel economy if I am able to coast enough with the added weight. Of course, the weight is coming out as soon as the weather improves.

[8307c4]

I'm not saying you can not do it, but I am saying for transmission longevity I recommend leave it in D always, also I am saying if you shift it you do so at your own risk.

Here's the thing, even if the chances of breaking it are but 1 in a million...
Who has to pay for it if (or when) it breaks?
You think one of these hot shot shift pros here are going to spring for it?
Personally I think you have to pay for it, if it breaks.

Yes, it can go flawlessly hundreds if not thousands of times.
All it takes is one time, one mistake, one bad luck moment.
What slowed me down is the price of a rebuild, and the fact most transmission specialists say the same thing: You want fail-safe operation then leave it in D.

That having been said, I do coast in N. :p
Hahaha but I have to say these things, I don't want nobody crying the blues if their tranny craps out for any reason.

Don't push the shift lock button (or pull forward on a column shift) when shifting between Neutral and Drive. This will prevent accidental shifts into Park, Reverse or the Low range. Just push the shifter back and forth.

Better yet, spend some time playing with the shift lock button and lever positions while the car is parked with the engine off to understand how it works. You should only need to depress the shift lock button to shift out of Park or to shift into Reverse, Park or the Low gears.

Until it malfunctions, or I shift so fast the detent mechanism fails to engage properly thus overriding the stop between N and R. Sometimes they break, sometimes they don't work like they should, my oldest car I can shift to-from any gear any time, doesn't matter when, how, or where.

Also column shifters work different from a floor shifter, but either one...

[tomatoman]

Has anyone tried something as simple as a drivers compartment switch to electronically cut out fuel injectors at the top of a hill, effectively shutting off gas completely while leaving the transmission engaged?
The idea just struck me.
It should be a very simple idea to test.
T man
33.15 mph 94 Maxima AT, fuel cocktail, see "garage"

[kamesama980]

Has anyone tried something as simple as a drivers compartment switch to electronically cut out fuel injectors at the top of a hill, effectively shutting off gas completely while leaving the transmission engaged?
The idea just struck me.
It should be a very simple idea to test.
T man
33.15 mph 94 Maxima AT, fuel cocktail, see "garage"

yes, search. also look under coasting with an auto trans with the engine off blowing up the trans threads.

[malherbe]

I maximize coasting to great benifit. I have a 99 vw passat 4c rated at 21 and 31. I regularly get 22 -28 by coasting. This is verified at the pump. It is true that the computer will read higher mpg's going down hills if left in drive, but i can go much farther and faster in nuetral. My car does have the fuel shut-off feature, and i never shut the car off while coasting. driving down hill in gear is like driving with the brakes on.

[dosco]

After looking at the SFC charts, I'm not convinced the savings are in the glide.

I am under the impression that the economy comes from maximizing the engine's operation at a certain BMEP and RPM range.

EDIT: After further consideration, I retract this comment. Brain fart, y'know.

[MarvHein]

I became a believer in neutral coasting with my Yukon XL, pulling my mostly city driving mpg up approx. 2 mpg.

Coincidentally (or not) my front diff threw a bearing and ate itself into total replacement. The tranny still seems fine and shifting back into gear after a glide has always been smooth.

Is there any way neutral glides technique could have damaged the front diff?

[PaleMelanesian]

600 mile highway trip last week in the Odyssey minivan. Rated 18/25 (old epa). 6 people on board, camping gear, and AC the whole time. Neutral coasting played a big part in the 28.5 mpg average for the trip.

[theholycow]

Were you doing those glides in 4wd? Unless that's the case, it's not possible for your neutral glides to affect it. It's separated from the transmission by the transfer case. With the transfer case in 2wd the front diff sees no difference between EOC, neutral coasting, cruising, and accelerating.

That front diff might be prone to such problems. What are the symptoms? My 2002 GMC Sierra front diff howls when I use 4wd. That's after 170,000 hard miles.

[sonyhome]

Neutral coasting with my CR-V saves fuel as per the ScanGage (no matter how off it is, I do arelative comparison of SG data in D vs SG data in N, so it is valid). Also SG seems about correct for MPG when calibrated right.

Coasting in "D" has 2 disadvantages on flats or light grades:
- Higher RPM (no cutoff for me since I don't get a 9999reading)
- Higher rolling resistance meaning shorter coasting

When I drive downhill on light grade, I coast in "D" to maintain constant speed.

When I coast on steeper hills I downshift to "2" or "1". However those incur higher RPMs and greater gas consumption (up to 1.2GPH if I recall right) so braking in D would be more efficient there, but would burn the brakes.

The Del Sol which has much less roll resistance coasts farther so I can milk coasting much more in city driving.
There I'm thinking cutting off the engine would save a lot of gas because the engine would be off like 50% of my commute distance. However I'm not willing to risk that even though it is a stickshift car.

What I have not figured out yet is what is the most efficient way to accelerate (soft, semi-hard, hard acceleration). I believe slow accelerations are not F/E. I want to go in coast mode ASAP, and also I believe slow accel at low engine RPMs is not efficient because you want to accelerate in the car's highest torque RPM range. Should start a thread on that!


BTW, N coasting in A/T does bug a lot passengers not used to this weird driving behavior.

[dosco]

What I have not figured out yet is what is the most efficient way to accelerate (soft, semi-hard, hard acceleration). I believe slow accelerations are not F/E. I want to go in coast mode ASAP, and also I believe slow accel at low engine RPMs is not efficient because you want to accelerate in the car's highest torque RPM range. Should start a thread on that!

I am wondering the same thing with my automatic transmission Camry. My initial P&G tanks - where I tried accelerating "hard" to about 2000 to 2500 rpm followed by glide - were disappointing.

Since then I've been accelerating gently. On the highway I accelerate by trying to keep rpms at or below 2200 rpm. When I get to my desired cruising speed, I start to P&G, with pulses fairly gently by trying to keep max rpm at or below 2200 rpm.

So far the results are promising, although I've been interested in running some math/physics to gain more understanding of the problem.

[sonyhome]

I am wondering the same thing with my automatic transmission Camry. My initial P&G tanks - where I tried accelerating "hard" to about 2000 to 2500 rpm followed by glide - were disappointing.

Since then I've been accelerating gently. On the highway I accelerate by trying to keep rpms at or below 2200 rpm. When I get to my desired cruising speed, I start to P&G, with pulses fairly gently by trying to keep max rpm at or below 2200 rpm.

So far the results are promising, although I've been interested in running some math/physics to gain more understanding of the problem.

You are driving an A/T camry, so it probably tries to be FE by accelerating in the higest gear (aka straining the engine).

Have you tried to force a downshift with a kick acceleration, then release the pedal right away to accelerate only at the right amount?
Neither flooring or slow accel IMHO are the answer. It's in between.
BTW I started a thread on that topic here:

How to accelerate in P&G mode? (http://www.gassavers.org/showthread.php?t=7782)

[dosco]

You are driving an A/T camry, so it probably tries to be FE by accelerating in the higest gear (aka straining the engine).

I control the engine, light on the throttle causes upshifts, harder on the throttle causes downshifts.

The point I was trying to make is that I'm not sure if it is more FE to accelerate with light throttle or heavy throttle. On my work commute, I tried heavy throttle at short duration (i.e. attempting to maximize BSFC) and got about 28 mpg (which isn't much better than my normal driving) and with light throttle and paying attention to keeping rpm at or below 2200, FE is now about 32 mpg.

Saw your thread.

Interesting to note Pale's comments that indicate light throttle to highway speed, followed by P&G with heavy throttle.

[sonyhome]

That's a 15% FE gain... For your camry I guess light is better! That's why camrys are always so slow on the road :-)

One reason may be that A/T could loose a lot of the energy in the slushbox with hard acceleration.

[theholycow]

Saw your thread.

Interesting to note Pale's comments that indicate light throttle to highway speed, followed by P&G with heavy throttle.

I saw it too. I disagree with Pale with one caveat. If and only if you can control your shift points, heavy throttle is still better, regardless of whether you're accelerating to cruising speed or already there and pulsing before a glide.

With an automatic that doesn't give you a good interface/good control (or whose torque converter is too lossy) light or medium acceleration wins easily.