Corolla 07 Coasting on Neutral?

Discussion in 'Fuel Economy' started by sergioschr, Jul 17, 2008.

  1. sergioschr

    sergioschr Member

    So I have checked Dinghy Towing vehicle list for flat towing and 2007 Automatic Corolla is not flat towable (so as approximately 90% of other automatic cars). Does this mean I cannot coast on neutral period? No rolling to stop on neutral with engine off? What are my options? Can you guys please advice.
  2. azraelswrd

    azraelswrd Well-Known Member

    You can probably still coast in neutral with the engine on or just coast in gear. (I do the latter the most for the fuel cutoff and because there are so many stops in my routes)
  3. AirGibson

    AirGibson Member

    Coasting in Neutral with an Automatic is pretty rabidly debated. There are several issues that repeatedly will come up:

    1) Will it damage the automatic transmission if I FAS?
    If you begin a coast in Neutral and turn off the engine (FAS), this can cause bad things to happen if your vehicle is not "flat towable" since it isn't properly pumping fluids in the transmission when turned off. You should not do this in an automatic ever unless you have a car that is "flat towable", meaning it can be towed with the engine off, in neutral, with all 4 wheels on the ground (behind a motorhome, for example). Your owners manual will tell you this. If your car requires that some of the wheels be off the ground or on dollies while towing, then that means you likely do not want to FAS with that vehicle.

    2) Will it damage the automatic transmission if I use NICE-On coasting?
    If you begin a coast in Neutral and leave the engine on (NICE-On coasting), this is generally okay. The question comes from when you put it back into D while still coasting. You will hear three different things:
    - Many people insist that this will cause a lot of stress on the transmission (usually the torque converter) to force the engine up to matching RPMs as you re-engage the transmission.

    - Some others will insist that in most modern transmissions, the extra wear can be made a non-factor by rev-matching the engine before re-engaging D.

    - And others will tell you that even a rev match is not necessary. Further in this thread, MaxxMPG goes into excellent and specific detail about why a N->D shift while in motion is okay in most modern automatic transmissions and why even a rev-match isn't necessary. ​
    From everything I have read, the issue of whether or not this is bad for your vehicle will depend on your specific vehicle's transmission. If your owners manual specifically warns you about transaxle damage if you coast in Neutral, then it would probably be wise to heed that warning and avoid NICE-On Coasting.

    3) Is it more fuel efficient in an automatic to coast in Nuetral, or to leave it in D and engine brake?
    This is the other biggest part of the debate. The important things to remember are:
    - Most fuel injected vehicles make use of a Deceleration Fuel Cut-Off (DFCO) feature while engine braking (aka Coasting while in D). The engine will stop consuming fuel while the momentum from the wheels continues to power the engine, thus causing some “braking” on your wheels. It will do this until RPMs drop to a certain point, and then the engine will begin using fuel to keep the engine at the idle RPMs. Thus, if you are engine braking above idle RPMs, you are usually using no fuel. While “not using fuel” sounds great, the fact remains that your engine is braking your vehicle. Braking is, of course, not exactly fuel efficient. Also note that DFCO sometimes has other limitations depending on the car model. Some engines may only use DFCO at high speeds, for example.

    - The opposite is true of Neutral. Your vehicle will free wheel with no braking being caused by the engine, allowing it to gather more speed down a bank or coast much further, much faster than when engine braking. While free-wheeling without using the engine sounds great, the trade-off is that the engine is burning idle fuel the entire time to maintain your engine’s idle RPMs. Burning idle fuel is, of course, not exactly fuel efficient.​
    Both methods will achieve better mileage than the other depending on the circumstances. The easiest hard & fast rule would be this:
    - If you know you are going to need to slow down or stop after the coast anyhow (e.g. approaching a red light), or if coasting in Neutral will take you to unsafe speeds (e.g. down a mountain), then engine braking often makes sense.

    - If you will not be needing to brake after coasting (e.g. on a decent stretch of slightly downhill highway), or if engine braking will be so slow that it still has to burn fuel anyhow to maintain engine RPMs, or if your vehicle only uses DFCO at high speeds, then Neutral coasting may yield better results.

    4) “It’s illegal to coast in Neutral in many states!”
    Many of us liken this to jay-walking, while others will say it is the equivalent of eating babies. This is up to the individual. The point is undeniably true, though, that it is illegal in many states.

    5) “You can’t stomp on the accelerator to avoid an accident while in Neutral! Engine braking could also give you more control in a bad situation!”
    No defensive driving technique I’ve ever heard of involves “stomping on the accelerator”, but people try to think of specific scenarios to validate these points of view. The point is certainly true, though, that you would not be able to accelerate while in N. Again, how much “fear” you attach to this is up to you.

    There are other points you’ll read about, but these 5 come up the most often. So in the end, some people will say this: “It is illegal, it might be more dangerous, and it might cause transmission damage. None of this is worth what tiny extra bit of fuel efficiency you might get from the occasional situation where engine braking isn’t as efficient.”

    Personally, I have never even met someone who was stopped for coasting in Neutral, I think the “dangerous” aspect of it require people to think of pretty obscure scenarios, and the issue of extra wear on the transmission completely depends on the vehicle. Just be sure to dig into your owners manual and look to see if any of these Neutral or towing warnings exist before you try. EDIT: Based on further discussions in this thread, I've updated parts of this post.
    Last edited: Jul 24, 2008
  4. kmactavi

    kmactavi Well-Known Member

    AirGibson, an excellent summary of what needs to be considered.

    I agree that the gains of NICE-On coasting would be small compared to DFCO when approaching a stop. It also allows you to fit in with normal traffic flow a little more, since coasting from 55 mph down to 15 in neutral would annoy most drivers. However, they are gains nonetheless and they add up if you are using this technique a lot (city driving). You might find that the convenience of DFCO makes it your preferred method.

    That being said, I disagree with the general statement that the gains of NICE-On coasting are small. When used in conjunction with P&G there can easily be gains upward of 30%. FASing during P&G adds another 5-10% gain, but the majority of the gain is from coasting with the engine disengaged. (DFCO is not effective for P&G)

    As AirGibson said, there are methods that yield greater results such as reducing speed and DWB, but if you have already mastered those and are looking to P&G as your next step, neutral coasting in a P&G routine will give large gains when implemented correctly.

  5. AirGibson

    AirGibson Member

    P&G is no doubt a way to improve efficiency, but wouldn't you say that doing the P&G routine (minus the FAS) in an automatic is really pushing it? IMO, we are barely able to justify the D --> N --> Rev-Match --> D routine while at speed. If you're repeatedly doing this once, twice, or three times per minute to to an automatic "planetary" style transmission, even I would have to question the wisdom of that.

    If it is a CVT transmission, then that changes the topic entirely for me as I don't know much at all about them.
    Last edited: Jul 17, 2008
  6. kmactavi

    kmactavi Well-Known Member

    Well, check out this post by Wayne.

    "I HS P&G the Accord quite a bit throughout much of Chicago’s Interstates to vastly improve her highway FE"

    His Accord is an automatic.

  7. AirGibson

    AirGibson Member

    I have no doubt there are people that do it, just like there are some people who FAS in automatics as well :eek:

    Is it a good idea to P&G (without FAS) in an automatic with rev-matching? I don't think anyone can really point to empirical data one way or another as far as tranny wear goes. All we'll have is relatively unimportant anecdotal bits like "My tranny is fine and I do it" or "I blew my tranny doing this". Until it's known for certain, exercising some moderation is probably wise. Or if someone knows of good data showing the actual wear on a tranny from doing a N --> D transition every few seconds at interstate speeds with rev matching, I'm all ears.
    Last edited: Jul 17, 2008
  8. PaleMelanesian

    PaleMelanesian Beat the System Staff Member

    There is ONE case where you might need to "stomp on the gas". My wife was driving. She signaled her left turn, and slowed to a stop due to oncoming traffic. So did the driver behind her. The third driver didn't see either set of brake lights, apparently. :confused: That driver rammed right into the back of driver #2. My wife, thinking quickly, floored the gas and barely got out of the way without being rear-ended.

    To summarize:
    waiting for a left turn, in traffic, driver behind not paying attention.
  9. MaxxMPG

    MaxxMPG Hasta Lavista AAA-Vee Von't Be Bach

    You're right, your Corolla is not flat-towable. This means you should avoid coasting at speed with the engine off. But it does not mean you cannot shift to N and leave the engine running - that is still ok to do. Just be sure when you move the lever from D to N that you don't press the button on the shifter. If you don't press the button, the reverse lockout will prevent you from overshooting N and ending up in Reverse. You can also move the lever from N back to D without pressing the button. So get into the habit of moving the lever with the palm of your hand, or move the lever shaft rather than the grip at the top so you don't run the risk of shifting to reverse and tearing up the motor mounts or CV joints or exhaust coupling.

    When shifting back to D, there is no need to rev-match as you often need to do with a manual. In N, the converter is unlocked, and since it is a fluid coupling, it will absorb any speed differential between the engine flexplate and the transmission's main shaft. There is no more transmission wear going from D to N to D to N than there is from normal shifting sequences, up and down through the four forward speeds.

    Most cars have no problem with being shifted back and forth between D and N. Wayne wrote recently that he had a rental Lincoln Aviator one time that was an exception to the rule. He wrote, "I would stay away from the Ford Auto’s in the behemoths however. I was in a Lincoln Aviator rental a few years back and coming out of a Fas, it had no idea what gear to be in, what R’s it should run at or when to actually reengage. It was a danger trying to bring that monster back online. GM’s big iron with Auto’s, smooth as a babies bottom" So while Ford's rear-drive transmissions (4R55* and 5R55* and possibly others) seem to have a problem getting back into Drive, I don't know of any other geared (non-CVT) automatics that have the same issue. The issue is not due to the mechanical or hydraulic design of the unit. It is related to the transmission computer being programmed only to start in first gear while stopped when shifting to drive, and so the output shaft sensor sending along a "high road speed" number causes computer confusion as the little electronic brain can't understand why the car is moving so fast without the lever in Drive.

    Many if not most CVTs should never be shifted to N at speed, as this will cause damage when shifting back to D.

    The question most people ask is when it is prudent to coast in Neutral.
    - For downhill glides, or when you want to lose speed as you approach road conditions that dictate a lower speed, just coast in D with the engine running by taking your foot off the accelerator. If the revs are high enough (over 1100-1500, depending on the engine), the fuel is cut off and so the engine is not burning gas anyway. So there is little point in worrying about shutting it down.
    - For the longest possible glide with the least loss of forward momentum, shift to N and coast with the engine on. The engine will burn anywhere from 1/4 to 3/4 of a gallon per hour idling in N. For most engine-on coasting, the amount of gas burned is small and not worth worrying about if the car is not flat-towable.
    - If your car is flat-towable and you want the longest possible glide without burning the little bit of gas the engine uses while idling in neutral, than the NICE-off glide is on the table for your use if you are experienced and comfortable with it. If the car is not flat-towable, the slight fuel savings will not offset the potential repair bill if the transmission is damaged by the forward motion without lubrication.

    The Corolla is capable of some pretty impressive MPG numbers. And as hypermilers, we research and learn and share ideas and knowledge and then apply what we learn to beat our EPA numbers. But we do so by selectively choosing different techniques from the hypermiling buffet table, using only what we feel is safe for our driving environment and our vehicles. We try out new techniques in isolated environments, away from traffic, so we can see what works for us and for our cars. Then we perfect them over time in our daily driving. While the Corolla is not the car for FAS'ing at speed, there are plenty of other treats on the table for you to select and perfect. NICE-on and some P&G around town will increase fuel economy without having to worry about the transaxle.
  10. MT bucket

    MT bucket I want my MPG!

    I had an incident once on a snowy day I was in a ranger pickup at a red light and it turned green, I started to go when an ambulance came into the intersection really fast. I stopped to let him by and looked in the mirror and saw a car locked up and sliding towards my rear end.
    I hit the gas to get out of his way, and it would have worked, except for one thing,
    my rear wheels were on i c e ! They just started spinning and I went nowhere! Crunch! he put a nice little ding in my bumper, but he messed up the front of his buick really bad!:rolleyes:

  11. AirGibson

    AirGibson Member

    I have a hard time swallowing this. The reason going from N->D is different than a normal gear shift is because there can be a much greater difference in the speeds of the components. Taking it to the extreme, to say "there's no need to rev-match" is to likewise imply that there is no wear on the transmission to rev up to 7000 RPMs in N while sitting at a dead stop and then slam it down into D to peel out. Do you think "there is no transmisison wear because it is a fluid coupling that absorbs the shock" in a case like that? While the converter might be okay, I cannot imagine that the clutches themselves escape without significant wear. I do not think that just because it is a fluid coupling makes any amount of differential in component speeds okay, but I confess that I am not as educated as some of the other folks.
  12. kmactavi

    kmactavi Well-Known Member

    AirGibson, bump starting with a manual transmission brings the RPMs from 0 RPM to idle 9500 RPM, just as big an RPM jump in my car as idle to cruising at 55 mph at 1900 RPM. Manuals to not have a torque converter for a more gradual spin-up, so it would be even harder on them. Bump starting is a commonly accepted practice, and people here have 100s of thousands of miles on their original clutches (mine is at 250,000 km). This would lead me to believe that with the cushion of the torque converter and a modern ECU which selects the appropriate gear, it is not a problem.

    I asked MaxxMPG to look at the thread since he knows a lot about auto transmissions.

  13. Damionk

    Damionk DWL Lover

    I have learned a few things from your post AirGibson. Thank you. One thing I do is keep my hand on the gearshift when I am in a NICE-on coast with my foot over the brake. That way if for some reason I do need to accelerate hard it will take as much time as it takes for me to put my foot on the accelerator since my right hand is ready to go back to drive in the same moment. It does make it easier since my gearshift is on the floorboard. My foot is over the brake during the coast so as to depress it enough to light up my brake lights to alert anyone behind me that I'm slowing.
    Last edited: Jul 18, 2008
  14. MaxxMPG

    MaxxMPG Hasta Lavista AAA-Vee Von't Be Bach

    There is a big difference between N to D while coasting and while the engine is runnning at 7000rpm. What most people miss in these discussions is that transmissions have overrunning clutches - either sprag or roller type - to allow the output shaft to freewheel. These clutches serve two major purposes.

    First, they allow smooth shifting of gears by absorbing the sudden change on output shaft speed as the shift from a 2.5:1 gear to a 1.5:1 gear occurs. There would be an awful 'bang' if this happened without an overrunning clutch that allowed the clutch drum to freewheel. When you shift to Low and you feel the engine braking, what you are feeling is a band or clutch applying to prevent that freewheeling.

    Second, they allow the output shaft to spin faster than it would spin if powered by the engine while in Drive. Unless Low range is selected, and a band/clutch applied to prevent the overrunning, the car will freewheel.

    Anyone who has ever ridden a multi-speed bicycle has had first hand experience with with a sprag clutch. There's one in the hub of the wheel or pedal crank to allow you to stop pedaling while the bicycle keeps moving. While bicycles don't have "Neutral", you can stop pedaling at any time, and that is analagous to N in that power is not being transmitted. If you start pedaling again, power will be transferred to the wheel as soon as you pedal fast enough to "catch up" to the road speed for the given "gear". Transmissions have a fluid coupling which makes this action even smoother.

    So on the highway, shifting from N to D, the transmission will apply the forward clutch and the direct clutch. Transmission designs vary widely, but most will apply two clutches to provide direct drive. At a lower road speed, 2nd or even 1st may be selected. Either way, if the wheels and output shaft are spinning faster than they need to, the sprag clutch will allow this difference in speed.

    So you don't need to worry about shifting N to D to N and so on. It's not the same as a 7 grand "neutral drop". If there were any chance of abnormal wear (or worse), the manual would clearly state that this shifting action would damage the transmission. Or, the transmission controller would be programmed to refuse to select a gear when moving back to D.
  15. Skwyre7

    Skwyre7 Well-Known Member

    Keep in mind that in N the RPM's are in the 700-900 range, and when you shift back to D at, say, 50 mph, the RPM's will be in the 1000-1200 range, because you'll be coasting in D at that point. So the speed differential isn't that great. (With your foot on the accelerator, maintaining 50 mph, the RPM's will be higher, obviously. But again, that's not the case directly after shifting from N --> D.)
  16. MaxxMPG

    MaxxMPG Hasta Lavista AAA-Vee Von't Be Bach

    In N, the engine speed will be the 700-900 you specified. And 50mph would correspond with 1000-1200 in overdrive with the converter locked. In direct drive with the converter unlocked, the actual "where the tach should be" is closer to 30-35% over that rpm, or 1300-1600. So shifting back to "D", the input shaft is spinning at about 700. The output shaft (now spun back up to speed because of the shift to D) is at 1400, or twice the speed. Reading my previous post above about overrunning clutches, you an see how the "input sprag" is designed to allow exactly this kind of freewheeling. The sprag is doing its job whenever the output shaft is spinning faster than it should relative to input shaft speed times reduction of current gear. And it does its job very well whether the transmission is in N or D.

    If you ride a 10 speed bicycle, pedaling at a constant speed, and suddenly shift it to a lower "gear" the sprocket will freewheel with the typical ticking/chattering. If you shift back to a higher "gear" you will start transmitting power again because the gear reduction is now in a range where your constant pedal speed is where it needs to be to equal what's needed to maintain the given road speed. The same idea applies to the sprags and rollers in the auto-trans.
  17. USMCStang

    USMCStang Member

    After reading these posts, I've come up with a few questions.

    1. My 05 Freestyle has a CVT, and is rated for flat towing at 44 MPH in neutral, with the engine off. I would assume that this means I should not FAS any any speed over 44MPH?
    2. At any speeds, when coasting, if I shift to N with the engine still on, the RPMs actually rise, rather than fall to idle. I would assume the PCM is doing this in order to do somewhat of an "automatic rev match" for when I shift back to drive. Ultimately, this would actually HURT fuel economy in a coast if the engine is truly decoupled from the transmission, correct?
    3. Fianlly, when I am simply coasting, it seems that the CVT manipulates itself to be as close to a neutral condition as possible. I do not experience the engine braking that I would expect in any other autmatic car. Unfortunately, I don't know if this is coupled with DFCO or not. Is there a way to tell, short of hooking up a scangauge?

    Given the above questions, my hypothesis is that, at least in the case of my Freestyle, that a simple "right foot removal" will give me the best fuel economy when coasting, provided DFCO truly kicks in.
  18. Damionk

    Damionk DWL Lover

    When I was recently taking my sister's HCH out for a drive and to show my BIL about hypermiling I learned that her car has a CVT and that the MPG goes higher if you leave the car in drive. Maybe just because that is how that car operates or maybe the CVT. I also think someone posted earlier in this topic about never putting a CVT in neutral.
  19. MaxxMPG

    MaxxMPG Hasta Lavista AAA-Vee Von't Be Bach

    While you're CVT (known as the CFT30 or ZF-CVT) is rated for flat towing, the manufacturer is just stating that the transmission will not be damaged by forward motion up to 44mph in N with the engine off. So FAS is ok. But "flat towing" assumes the car is being towed. And this implies that the vehicle will be stopped and unhooked from the towing vehicle before it is started and shifted out of neutral.

    The apparent reason for the "no-neutral" limitation that so many CVTs have is that they are computer controlled and will revert to a "lowest possible ratio" reduction when the fluid pressure is released in N. The higher revs in Neutral are likely just the result of the computer trying to compensate for the radical difference between the input and output of the transmission.

    There is no easy way to tell if the engine is in DFCO without a scan gage.

    Check the owners manual to see if Ford states you should not shift to N while the vehicle is rolling. Another member with a Saturn ION with CVT quoted his manual that stated that the car should never coast in N. But this is highly dependent of the design of the CVT, and there may be some models that can coast in N without a problem. If your manual doesn't say anything either way, you can check with the dealer or with a reputable transmission shop. They should be able to read the service manuals to see how the transmission handles neutral while at speed.
  20. DocOc

    DocOc Well-Known Member

    just to add my 2 cents. i shift from D to N to D alot on downhills or when the road is empty enough to coast. i drive an auto tranny that is not flat towable. there is absolutely no 'bump' going from N to D at speed (80km/h and under), however there is a significant bump going from idle N to idle D (when starting the car at a red light for instance).
    if anyone can enlighten me as to why this happens, i would greatly appreciate it

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