# Coasting



## operator (Jan 2, 2015)

Has anyone else noticed that while coasting into a stop light or stop sign the engine really really slows down the car. I mean sometimes its so bad that ill have to give it gas to get to the stoplight or i wont make it. If i put in neutral this think will seriously coast for miles, reminds me of a well oiled pine wood derby car. Its astonishing because i would have thought GM would have engaged the "clutch" (excuse my lack of knowledge on the automatic transmissions(**** things are complex)) while coasting to help improve gas mileage.


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## au201 (May 18, 2013)

operator said:


> Has anyone else noticed that while coasting into a stop light or stop sign the engine really really slows down the car. I mean sometimes its so bad that ill have to give it gas to get to the stoplight or i wont make it. If i put in neutral this think will seriously coast for miles, reminds me of a well oiled pine wood derby car. Its astonishing because i would have thought GM would have engaged the "clutch" (excuse my lack of knowledge on the automatic transmissions(**** things are complex)) while coasting to help improve gas mileage.


The reason it does that is actually a gas mileage feature. It's called deceleration fuel cut-off (or DCFO). When DCFO activates the torque converter (auto) locks to keep the revs up and the car cuts off all fuel to the injectors. Coasting in neutral actually uses more gas because the car has to use gas to keep the engine running where as in gear it can use the wheels momentum to keep the engine spinning without fuel. So you are better off leaving it in drive fuel economy wise. 

That probably makes no sense though seeing as it's late and I've been up for a long time ?

Sent from AutoGuide.com Free App


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## BU54 (Nov 24, 2014)

That makes sense. I like getting 99+ MPG when coasting to a stop or driving downhill.


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## cdb09007 (Aug 7, 2013)

DFCO ALL DAY ERY DAY!

.....except when accelerating....


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## Barefeet (Jan 1, 2014)

I Disagree. I don't like driving to a stop sign. When I come home I can coast 1/2 to one mile (depending on the wind) in neutral to the end of the expressway ramp. The DIC reads 99mpg. I drop it back into gear the last tenth of a mile to slow down. If I drive that last mile in gear the DIC will be at 50 to 60 mpg until I decelerate I understand their thinking, but there is a lot of friction to keep that engine spinning even without fuel it slows the momentum of the car so you have to drive further before decelerating.


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## obermd (Mar 3, 2012)

Barefeet said:


> I Disagree. I don't like driving to a stop sign. When I come home I can coast 1/2 to one mile (depending on the wind) in neutral to the end of the expressway ramp. The DIC reads 99mpg. I drop it back into gear the last tenth of a mile to slow down. If I drive that last mile in gear the DIC will be at 50 to 60 mpg until I decelerate I understand their thinking, but there is a lot of friction to keep that engine spinning even without fuel it slows the momentum of the car so you have to drive further before decelerating.


What are your RPMs? What you're describing is what I see in my ECO MT if I coast in gear but let the RPMs drop below 1250.


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## Barefeet (Jan 1, 2014)

obermd said:


> What are your RPMs? What you're describing is what I see in my ECO MT if I coast in gear but let the RPMs drop below 1250.


Coasting with the automatic transmission in neutral, the rpms are 800.
Coasting with the transmission in drive the rpms will be 1200 to 1400 as it downshifts.
The fuel injection may shut down, but the drag from engine friction plus pumping air thru the valves greatly reduces the coasting distance.
I enjoy shifting to neutral. I doubt GM would tell people to do it.


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## obermd (Mar 3, 2012)

Barefeet said:


> Coasting with the automatic transmission in neutral, the rpms are 800.
> Coasting with the transmission in drive the rpms will be 1200 to 1400 as it downshifts.
> The fuel injection may shut down, but the drag from engine friction plus pumping air thru the valves greatly reduces the coasting distance.
> I enjoy shifting to neutral. I doubt GM would tell people to do it.


At 800 RPM you're burning gas. If your coast started above 1500 RPM your car will not burn gas the entire time it's decelerating, including through those downshifts. The AT downshifts just before the ECU has to turn the injectors back on.

What are your tire pressures? The Cruze has very little aero drag at low speeds so we need to look elsewhere for the drag. Under inflated tires are a good place to start. Even the door placard pressure is under inflated for fuel economy purposes.


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## spacedout (Dec 7, 2010)

There is some places using neutral can gain you a bit more distance from coasting, but you should utilize DFCO as much as possible by coasting in gear. 

Neutral burns as much fuel as idling, coasting in gear using DFCO uses none.


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## Merc6 (Jun 8, 2013)

Yep, tire pressure can be the issue as I coast in gear most of the time in clear roads. In snow I try to stay in gear so I can let out the clutch and engage stabilitrac if I need to panic stop.


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## operator (Jan 2, 2015)

does the diesel have this DFCO?


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## iedgar10 (Sep 25, 2014)

This is odd... I actually have the opposite problem... I find myself using the break a lot even if I haven't touched the gas pedal... It takes about half a mile to drop from 45 to 10-15mph on flat surface... I'm averaging 25mgp with 20mph average for the last 7000 miles according to DIC

And isn't shifting from neutral to drive in an automatic discouraged while the car is moving?


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## spacedout (Dec 7, 2010)

iedgar10 said:


> This is odd... I actually have the opposite problem... I find myself using the break a lot even if I haven't touched the gas pedal...


My car is the same way, however there are a few points(28MPH) downshift from 5th to 4th that the ratio change causes a significant change in how fast your loosing speed. My previous cars were not like that so it takes some getting use to. There are still times I let off a bit to soon and end up giving the car some gas for a few seconds to make sure I make it to the stop sign/light. 



iedgar10 said:


> And isn't shifting from neutral to drive in an automatic discouraged while the car is moving?


No problems at all, just don't rev the engine up and drop it back into gear. Just like with all other cars when shifting back to D just watch the tach for it to jump back up to the proper point for the given gear/speed or wait a second or two before getting back into the gas.


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## Robby (Mar 1, 2013)

iedgar10 said:


> This is odd... I actually have the opposite problem... I find myself using the break a lot even if I haven't touched the gas pedal... It takes about half a mile to drop from 45 to 10-15mph on flat surface... I'm averaging 25mgp with 20mph average for the last 7000 miles according to DIC
> 
> And isn't shifting from neutral to drive in an automatic discouraged while the car is moving?


For starters, you are comparing your gasoline 1.4 to the OP's Diesel......this is the Diesel section.

The diesel, like any diesel, has far more compression braking than a gasser and because the automatic doesn't disengage on coast, like they did years ago, the diesel almost feels like you applied the brakes somewhat when the accelerator is released.

Our little 1.4 gassers.....not so much.....auto or manual they coast far longer....weight of the car easily drags the engine along regardless of throttle position.

Just about every design automatic produced since around 2005 and onwards, regardless of gas or diesel fueled, stays engaged during coastdown.
A combination of potental fuel mileage enhancement with the benefit of being in the right gear when the throttle is reapplied.

One of those things that define the operation of late model designs, you learn to use it to your advantage.....mostly timing stoplights and the like.

Rob


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## obermd (Mar 3, 2012)

operator said:


> does the diesel have this DFCO?


The North American Diesel does. I was able to test this during a test drive. I don't know about the other Diesels around the world.


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## Barefeet (Jan 1, 2014)

obermd said:


> What are your tire pressures? The Cruze has very little aero drag at low speeds so we need to look elsewhere for the drag. Under inflated tires are a good place to start. Even the door placard pressure is under inflated for fuel economy purposes.


This car coasts great (Tire pressure 41 cold goes up to 44 when warmed up). I'm not an engineer, but it seems to me that if I can coast a half mile or more in neutral burning a little diesel (99 mpg) and then drop it into gear the last tenth to decelerate naturally burning no diesel I am probably using less fuel than I would if kept my foot on the accelerator until the last tenth mile.
I may be wrong, but I like free wheeling "like a skate board".


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## spacedout (Dec 7, 2010)

Barefeet, I think in your example you are using less fuel to cover the same distance with the method you use. 

With the compression of the diesel you can't coast as far, so you would need to remain in gear and on the gas longer to cover the part your in neutral. I would assume a 99mpg idle burn in neutral is a higher reading than what you can get in gear on the gas. As long as you use DFCO when you can, your doing great.


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## jalaner (Dec 28, 2013)

You could possibly save a small amount of fuel by shifting to neutral but at the cost of increased brake wear. The engine braking is also a safety feature, decreasing the risk of brake overheating and failure on long downhills like mountain driving. I used engine braking a lot when learning to drive in a manual tranny car so I like it on my CTD. My 08 Vibe with AT also has engine braking.


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## PanJet (Jun 18, 2013)

I'm not sure if this is what you're talking about, but my diesel seems to have a lot more engine braking than the gas model does, and it feels intentional. It will lock the torque converter and shift down shoving up the RPMs and significantly slowing the car. It also seems to do it more when you're going downhill. 

I am purely theorizing here, but I've often wondered if the car is engineered to engine brake like this. I know GM's Allison tranny with it's Dmax engines was engineered to force some engine braking if the brakes were pressed while going downhill while in Tow/Haul mode. Perhaps since the CTD is a heavier car, they intentionally programmed the car to assist with downhill braking using the engine to save on the brakes a little. I have not seemed to notice it as much while coasting or braking on a flat surface.


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## Rivergoer (Mar 30, 2017)

Apologies for raising an older thread, I’ve been looking for information on the Gen 1 Diesel Aisin transmission and whether coasting in Neutral for extended periods (long downhills) is harmful in any way.

I was always told to NEVER coast an automatic transmission (90’s and older vehicles) because trans fluid was not circulating while in Neutral. Not sure if the Aisin has some sort of ‘pump’ that keeps fluid circulating to prevent damage.

I frequently drive stretches of westbound I-10 in California where it’s possible to safely coast at the speed limit in Neutral for several miles. Coasting while idling would seem to be more efficient than using combination of accelerator/DFCO to cover the same distances. 

The Diesel engine backpressure while in gear prevents the car from covering these distances without some gas pedal input. Thoughts?


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## sparkola (Jun 9, 2014)

Set the cruise control for your current speed and let the auto tranny handle it


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## sailurman (Sep 29, 2016)

Well, I had no idear!!!


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## sailurman (Sep 29, 2016)

DCFO it is then


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## anthonysmith93 (Jul 15, 2015)

I know this is the diesel section, but one thing I hate about coming to stops is how not linear/smooth the braking is. My 2005 malibu I could depress the brake pedal at one moderate level and the car would smoothly slow to a stop. The cruze (even with brand new pads and rotors) seems modulated and jerky, with even pedal pressure, and slows and then "catches" and slows more and "catches" and slows more then stops; this coupled with odd and inconsistent downshifts makes for an unsatisfying experience, and this isn't specifically Cruze related, I've noticed this in other newer cars as well, and it's irritating to say the least. 

So all in all, I WISH I could use the brakes less.


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## justin13703 (May 2, 2016)

Under normal driving conditions, just using the dfco feature as intended and not thinking about it is the best way to go.

When you start talking about drifting in neutral for so much of a distance, and then using dfco for so much of a distance, it starts becoming unrealistic as far as driving style. Yes that may save you a dollar of fuel a year, but me and a lot of other people don’t really want to be following someone around who starts decelerating like 3 miles ahead of time because they’re trying to drag another thousandth of a mile per gallon out of their car. It’s like saying you get better mileage by driving 30mph on the highway vs 70. That may be true, but it’s not something you should be doing.

While I’m here, I will say that I don’t feel like there is much engine braking with the diesel at all. But then again I like to get where I’m trying to go in a timely fashion, so I’m generally pretty close to where I need to stop, before I start slowing down.


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## jblackburn (Apr 14, 2012)

anthonysmith93 said:


> I know this is the diesel section, but one thing I hate about coming to stops is how not linear/smooth the braking is. My 2005 malibu I could depress the brake pedal at one moderate level and the car would smoothly slow to a stop. The cruze (even with brand new pads and rotors) seems modulated and jerky, with even pedal pressure, and slows and then "catches" and slows more and "catches" and slows more then stops; this coupled with odd and inconsistent downshifts makes for an unsatisfying experience, and this isn't specifically Cruze related, I've noticed this in other newer cars as well, and it's irritating to say the least.
> 
> So all in all, I WISH I could use the brakes less.


Torque converters stay locked on down to 2nd-3rd gear in most modern cars. It makes for jerky downshifts. Sometimes they'll cut on the injectors for a brief second while the shift is performed, and you feel a little bit of acceleration when it does.


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## 316106 (Jul 22, 2017)

I have long been with the impression a neutral coast in an automatic is okay because the engine idling circulates fluid in the trans. Flat towing with the car off is supposed to be the no-no. I disagree with the dismissive response inferring coasting as inconsiderate driving. Some of us just aren't around a rat race environment. And yes, the diesels have more compression braking. 

My Gen 1 from a fast neutral coast will go into 5th before shifting to 6th. It has dissuaded me from using the strategy. I also have rented newer Chevy vehicles with the L1-6 gear and going from D at speed, it'll dump you in 4th. I wish neither did that. I actually liked the L1-6 trans better because my cars manual mode isn't close enough to a real stick anyway.

I very much tend to agree with disliking how newer cars seem programmed to game against how you are trying to drive. Enough so to be looking to change cars. Although, I can see a programmer's dilemma when on a slight downgrade in a traffic jam, I can take off gently from manual mode in 2nd or 3rd; and then, drive through a steep downhill in town and feel that lock up jerk in 2nd (very useful for my commute).


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