Is it ok to brake after coasting towards a stop?
 

Hello all,

I've been debating this in mind for quite some time now and thought I would ask. I have a few questions...

First off, I drive an automatic. So I know that EOC and P&G is unsafe for my vehicle. I just coast in gear to engage DFCO and DWL on rolling terrain.

I always coast in gear whether to slow myself down or to take advantage of my DFCO. Where I live, it's flat to rolling hill terrain so I never have an opportunity to coast with engine on in neutral.

Question #1:Is it sensible, fuel economy wise, to brake after coasting to a stop? For example: Driving 45-50 MPH then coast down to 25 MPH before coming to a stop sign/stop light then applying the brake to stop.

I know that DWB is the way to drive efficiently but wouldn't the time it takes the vehicle to slow down to a stop and be in a lower gear be wasting more time and thus more fuel versus coasting down to a few MPH then using your brake to stop smoothly???


Question #2: I drive an automatic. Is it more efficient to shift to Neutral at stop lights or just keep it engaged in Drive to reduce wear on the transmission?

Am I taking full advantage of coasting? Am I doing this wrong?

If this has been addressed multiple times, I sincerely apologize.

Do you have a scangauge? That would be the best way to test it. I think it would be more efficient to coast to a stop in neutral. Only pressing the gas when needed. If the road goes from 50-20 slow down by coasting in neutral and come to a stop at the line. I would think this is the best way. If you are sitting at a red light you should be in neutral with the engine off. Even with it on it is better to have it in neutral and idle. A obd2 computer like a scangauge ultragauge or torque. Would be able to show you.

DWB is an ideal term, not a practical one. The idea is to minimize braking, not to coast to every stop. You're doing great.

I leave the minivan in drive when I'm stopped. I could examine gph while in neutral vs. in drive, but I've never really wondered.

edit: fat charlie beat me :)

Driving without brakes (DWB) isn't completely doable. It should really be called driving using the brakes as little as possible since you can't eliminate using them entirely. Every stop you make you use brakes, you just need to. If you can coast down from 45 to 25 mph before a stop thats pretty good IMO. The slower you coast down the better obviously.

I coast a fair amount in automatic transmission cars. The real test is when you put it back in gear (at speed), does it lurch? If it does, you can try to rev-match to minimize the lurch (I do this). Or, you can coast in gear (least efficient).

Idling in drive always uses a bit more fuel than shifting to neutral. On my Sunfire its about 8% more .

If you can come to a complete stop just by dint of gravity then that's one thing, but actually driving without brakes isn't actually practicable in real life. It's an ideal to strive for, that's all. The point is to not unnecessarily throw away any kinetic energy if at all possible.

I have UltraGauge. I don't slow down fast enough with my engine on in neutral. My car seems to coast for quite a long ways. Shutting off at lights worries me about extra wear on the starter and ignition.

My car has DFCO so that's why I figured leaving it in drive would yield better results.

Ok, that's good to know! Because I've been pulling my hair out nearly at having to stop every time LOL. I don't like stops but I'd rather not get a ticket or endanger lives either.

If I can safely "coast" through a stop sign at 15-20 MPH with nobody around then I will notice that lurch when I give it a certain amount of throttle but that's when it's in DRIVE, my guess is it's trying to up shift quicker??

Say you go from point A to point B the most efficient way would be to only use as much gas as needed to come to a complete stop at point B. We don't want to break any laws either because all that saved gas, would be gone with 1 ticket. I drive the speed limit or near it. If I have a turn I will coast before the turn so I am going a safe speed and don't need to hit the brakes. Go as fast as you want not all of us have all goddamn day to get somewhere. I do tho #!


Every car I have ever driven uses less gas in neutral at a stop Vs drive.

My ex-girlfriend insisted that the car used less gas in neutral than park, but I told her that it was not worth wearing out the transmission to go from 0.27 GPH to 0.25 GPH for an average of a minute or less, when the car was rated 25 MPG. If you drive 55 MPH on the freeway (limit 65), you use 2.2 GPH.

That's a good thing! If you have the time, and won't be annoying following drivers (who can't pass you), then start the neutral coast sooner. That'll save more fuel.

If you are *trying* to slow down faster than coasting in N, then using deceleration fuel cut-off in gear is more efficient than using the brakes. But coasting in N is generally more efficient than DFCO because you get off the accelerator (accel. or maintaining speed, burning the most gas) even sooner.

Also, your car only cuts fuel above a certain RPM, and possibly not at all in the lowest gears (your gauge may show you this). I recently drove a brand new Nissan 4-speed automatic that never cut fuel in 1st or 2nd gear.

I only know of one person who has worn out a starter while trying to save fuel, but he was shutting off at every single opportunity, including pulse & glide (automatic). Driving a Honda.

Stopping the engine when the car is stopped is worth roughly 5-10% better fuel economy in city driving, which is why auto stop/start is now becoming common on new cars (including non-hybrids).

Whether you should do it or not is entirely up to you.

I believe that I read on here that starting the engine uses the equivalent of eight seconds of idling.

My car uses just about 60% of the fuel when idling in N, foot on the brake, compared to idling in D, foot on the brake; even though it revs a bit higher, freed of the load.
That also makes it recharge the hybrid battery faster. So it does not only save me fuel then, it will also save me fuel later on.

Still I prefer AutoStop, not burning fuel at all now, even though it may need to compensate a bit later for the slight loss of charge.
I use less than 0.2 GPH idling in N. But then, I use about 0.4 GPH (1.5 l/h) at 38 mph. Sadly I need to go faster most of the time.

My advice is to coast it up to the light in neutral as quick as possible, and shut it down until you absolutely have to start it back up.

In the Black Widow, the very first hypermiling technique I ever employed was to simply shut it off at lights. I got an instant return of about 6 mpg on the tank! Then I was hooked!

Once your car is warmed up, it re-starts pretty easily, and unless your starter is an old p.o.s. you won't wear it out. Before I learned to bump start the Festiva, I would key start every time after EOC and P&G. I restarted that car literally thousands of times without killing anything

As far as coasting through stop signs, I never recommend anything like that. Hypermiling is a personal choice, but it shouldn't affect the other drivers you share the road with, unless you wanna give us all a bad name. 100% of my hypermiling is done without breaking any traffic laws (other than the Black Widow being off half the time) and without being a PITA to anybody around me.

I'm so glad to hear this. Finally, I don't feel insane or fretting anymore :)

One more thing...Is it advisable to remove the spare tire and jack in my vehicle? It's a full size spare and equipment. Will I see any gains by removing it?

Some of the traffic lights on my routes are no more than 8-10 seconds. Is that even enough time to shut down to see a change in FE?

I'd just coast down to those lights. 30 seconds or more is worth it, depending on the car. 10 seconds is rather marginal. Pulse-and-glide between lights properly and you shouldn't even spend any time stopped.

The weight of the spare has an effect, but it's not much. I'd take it out if you were going to the racetrack. On the street, it's probably not going to make a noticeable difference.

By coast, do you mean in Drive or in Neutral?

I have an automatic, so I don't think pulse and glide is safe nor efficient for my vehicle.

Two comments: Sailing through a stop sign at 15-20 MPH may get you a summons someday. You might save 5 cents worth of fuel, but on the day there is a waiting cop who is stealthier than you that you didn't notice, it may not be worth the fine incurred.

No automatic transmission will be damaged by coasting in neutral to a stop or a "near stop". That means you can safely re-engage into drive in first gear, at under 10 MPH. Rev matching at higher speeds may or may not be detrimental. There is usually no way to tell with absolute certainty. You may not realize it until your transmission needs to be rebuilt. The amount of $ you saved on fuel in coasting will seem a pittance compared to the cost of an A/T rebuild.

Pulse and glide with an A/T basically means getting it up to speed so as to get it into a higher gear, then taking your foot off the gas pedal completely, until you need to accelerate again. It amounts to "coasting" while still in "Drive".

I rarely coast through stop signs anymore, it's just not worth the risk.

I will try coasting in neutral and report my findings on my next fill up.

Ah ok! I already do this, so I have been P&Ging all along and never knew it. Awesome!

Coasting in Drive or Neutral... I personally don't see much difference in wear, as long as you don't get much slippage or stress on the clutch packs when getting back in gear... like XYZ says, from a stop, it's probably no big deal.

I drove a new MINI last month... in "Green" mode, it automatically goes into neutral when you let off the gas any time you're above 30 km/h. Kind of thumbs its nose at people who declare you will die a horrible death if you coast in neutral at highway speeds!

Yes, but in most places in the United States, it is illegal if you do this manually. Also, it sounds like engaging DFCO is quite an achievement.

In Sport Mode, it stays in gear. In Normal, it depends... it's less eager to go into neutral... but it seems like it still does.

I also seem to recall manual shifting or small prods of the accelerator or brake make it re-engage the clutch.

Who the hell cares. Seriously. Every time I press the clutch for more than a second I must be breaking the law.

How would they even know anyway? Yeah they wouldn't, no one would. My friends riding with me didn't even know I did it until I told them and they were in the car.
"Why do you keep going 60 to 45 over and over again?!"
"Its called Pulse and glide It saves fuel"
"Isn't it better to just go 50??"
"And have my engine on burning fuel the entire time I'm driving?? Hell NO"

I certainly do not encourage anyone to break the law, but this one makes as much sense to me as anything from You Can Get Arrested for That!?.

I was happy to read http://ecomodder.com/forum/showthrea...-mn-29077.html, although that law specifies that it is illegal to coast in neutral down a hill.

In some cases, but not always. For example, Honda automatics will hold it in gear and engine-brake if you leave it in D. That's not coasting. When I drive the Odyssey, I'm constantly shifting D-N-D-N to get any real coasting.

Some vehicles' transmissions are programmed to go into a nearly neutral state automatically, like what you're describing. GM trucks come to mind from my experience.

Absolutely true. It depends on the design of the transmission, how rudimentary or advanced it is, and how the electronic programs (on more recent years) are monitoring and controlling what it does. Unfortunately, there is no practical way to discover all the subtleties of an automatic transmission until after you have purchased a vehicle and experiment with driving it.

I also agree that it is confusing to call coasting while in Drive "coasting" at all. But compared to driving with your foot constantly on the gas pedal, it probably is somewhat more beneficial. ;)

;) indeed.

In the case of my Odyssey, it's a programming issue. They even call it a feature. :rolleyes: In certain uphill and downhill conditions, it even holds it in 4th gear instead of 5th. Drives me crazy!

You know you're an ecomodder if... ;)

Precisely what I do. I had a Riviera that would coast the same in gear as neutral. My guess would be they unlock the converter while staying in top gear, which also allows you to reengage the gears smoothly with maybe a slight throttle blip when reengaging at high speeds.

Coasting in neutral can net you periods of 100+MPG, never avoid them. The Sentra will shift to neutral and back to drive without having to even touch a button.

regards
Mech

Hey everyone,

So I tried coasting in Neutral yesterday on all of the areas where I leave it in Drive when I release the gas pedal. A few things I monitored...

-I coast just as far in neutral as I do in drive. It's no further. It slows me down at the same rate. I don't have any steep declines in my area. Just flat to rolling hill terrain.

-My UltraGauge shows 999.9 MPG while in Drive from 50 MPH down to 20 MPH. In Neutral, it shows 70-100 MPG at 50 MPH then declines from there as my speed drops. My Instantaneous Gallons Per Hour is .35 GPH while in Drive. It is .6 GPH while in Neutral. This is with no A/C on, nothing.

-When I shift from Drive to Neutral at 40-50 MPH, I feel a slight jerk and lurch. The sane happens when I reengage the transmission.



Based on this observation, it would seem that coasting in drive is more beneficial for my particular car than neutral. Is this strange? My UltraGauge is not calibrated.


One more note: On my last tank trip, I achieved my 37 MPG average using coasting in Drive. However, I also used DWL and no A/C as well.

If that's the case, I'd just leave 'er in D.

My car must be the black sheep. Unless my UG is off...

Are you using the 6 or 8 gauge display on the Ultraguage? The 8 gauge display doesn't always show DFCO, so I use 6 gauge.

Also, did you dial in the correct injector cutoff value in the menu? It's based on engine size & the intructions are in the manual, but don't have it available right now.

You describe having DFCO while in neutral, which does not sound possible. I am not doubting you regarding the 0.6 GPH in idle, but my Forester only uses 0.25.

It really depends on what you are doing. If you are a light-timing genius, you should never need to coast in-gear or use your brakes, while DCFO uses no gas and neutral uses a little, how much do you use accelerating back up to speed?

If you have a stop sign, would you prefer to drive at your city mileage and then DFCO, or coast in neutral for a much longer distance? That is, unless you have people behind you. I always do, all hours of day and night.

If you have a very gradual hill and you can roughly maintain your speed in neutral, that makes more sense than keeping it in drive and getting 40-45 MPG, because you could get 91.67 at 55 MPH.

If you have a steeper hill, you need to stay in-gear for engine braking, and sometimes you need to downshift.

My ex-girlfriend complained that the transmission was rough shifting between neutral and drive and then she replaced her transmission mounts. She is my ex-girlfriend, I try to avoid her and definitely not to help her think through her problems anymore, but I did try to explain that some repairs are not worth the money, and how terrible an idea it is to pay for things when it puts your account in overdraft.

I am using the 6 Gauge display. I have Instantaneous MPG and Instantaneous Gallons Per Hour displayed. I have the UltraGauge EM.


Yes I have set the DFCO according to my engine size.

No, I never said I had DFCO while in Neutral. It's only in Drive.
My apologies, I meant to type .25 GPH, not .35 GPH...(I'm using a mobile phone to type so my fingers keep missing the correct buttons.)

Whether I use Neutral or Drive to slow down to stop, I will still have to get back up to speed, so I am at a slight loss either way.


I guess I will need to try one tank on neutral coasting alone and another on DFCO. I just really don't want to risk having to replace my transmission for $3,000+...