Don't do this
10-08-2013, 07:21 PM
#11
AudiWorld Super User
10-08-2013, 08:59 PM
#12
Still, I would not do this for the reasons others have posted.
10-08-2013, 11:16 PM
#13
AudiWorld Senior Member
Join Date: Apr 2009
Location: Washington State
Posts: 720
Likes: 0
Received 0 Likes
on
0 Posts
This simply isn't true. Coasting while you are in gear will allow the engine to actually shut off the flow of fuel since the drive train will keep the engine turning over. If you coast while in neutral (or out of gear), fuel will still have to flow to keep the engine turning over.
10-09-2013, 03:18 AM
#14
AudiWorld Super User
Speculating a bit here, but based on the original post, I think the reason is to avoid the drag of engine braking. In that sense, there is a fuel savings benefit because the car will "coast" further in Neutral than in will in Drive. If you time it perfectly, you can release the accelerator pedal earlier, which theoretically should save some finite amount of fuel.
Still, I would not do this for the reasons others have posted.
Still, I would not do this for the reasons others have posted.
10-09-2013, 06:11 AM
#15
Actually, I did check out those resources, and what I am saying is not inconsistent with them. Those resources confirm that the rate of fuel consumption is no different at idle, regardless of whether the vehicle is in Drive or Neutral. I agree with that.
However, I think the original poster was making a different point that those resources do not address. Just for the sake of discussion, I will clarify my point.
[Disclaimer: In practice, particularly with an automatic transmission, I suspect the actual fuel savings would be so small as to be negligible, and in any event, shifting into neutral is a bad idea for the reasons others have posted.]
With the transmission in Drive, more of the drivetrain is engaged, which causes a (slightly) higher drag on the wheels, which slows the vehicle. All other things being equal, this increased drag will bring the vehicle to a stop a little bit sooner in Drive than in Neutral. As a result, the vehicle theoretically will coast a little but further in Neutral than in Drive. As the linked resources demonstrate, during the coasting period, the engine's idle speed fuel consumption would be the same in either Drive or Neutral, so there is no fuel savings there. However, the fact that the driver can release the accelerator pedal a little bit earlier before coasting in Neutral than in Drive to coast to a stop at the same spot (i.e., a stop sign) means that the vehicle uses a little bit less fuel before coasting in Neutral.
In other words, assume the vehicle will coast 500 feet in Neutral. In Drive, it would coast slightly less than 500 feet. If the driver plans to coast in Neutral, he can release the accelerator pedal 500 feet before the stop sign. But if he plans to coast in Drive, he cannot release the accelerator pedal until the vehicle is at a distance somewhat less than 500 feet from the stop sign. To make up for the difference, the driver must continue applying the accelerator pedal a little bit longer before coasting in Drive, during which time the engine is consuming slightly more fuel than it would at idle.
In theory, this makes sense and would result in a small fuel savings. I wrote "finite"' in my last post because I think the actual amount would be very, very small. Particularly with an automatic transmission, where the torque converter eliminates almost all engine drag at idle speed, the additional drag of Drive compared to Neutral (and therefore the resulting fuel savings in Neutral) would be extremely small -- certainly not enough to justify the safety issues caused by coasting in Neutral.
However, I think the original poster was making a different point that those resources do not address. Just for the sake of discussion, I will clarify my point.
[Disclaimer: In practice, particularly with an automatic transmission, I suspect the actual fuel savings would be so small as to be negligible, and in any event, shifting into neutral is a bad idea for the reasons others have posted.]
With the transmission in Drive, more of the drivetrain is engaged, which causes a (slightly) higher drag on the wheels, which slows the vehicle. All other things being equal, this increased drag will bring the vehicle to a stop a little bit sooner in Drive than in Neutral. As a result, the vehicle theoretically will coast a little but further in Neutral than in Drive. As the linked resources demonstrate, during the coasting period, the engine's idle speed fuel consumption would be the same in either Drive or Neutral, so there is no fuel savings there. However, the fact that the driver can release the accelerator pedal a little bit earlier before coasting in Neutral than in Drive to coast to a stop at the same spot (i.e., a stop sign) means that the vehicle uses a little bit less fuel before coasting in Neutral.
In other words, assume the vehicle will coast 500 feet in Neutral. In Drive, it would coast slightly less than 500 feet. If the driver plans to coast in Neutral, he can release the accelerator pedal 500 feet before the stop sign. But if he plans to coast in Drive, he cannot release the accelerator pedal until the vehicle is at a distance somewhat less than 500 feet from the stop sign. To make up for the difference, the driver must continue applying the accelerator pedal a little bit longer before coasting in Drive, during which time the engine is consuming slightly more fuel than it would at idle.
In theory, this makes sense and would result in a small fuel savings. I wrote "finite"' in my last post because I think the actual amount would be very, very small. Particularly with an automatic transmission, where the torque converter eliminates almost all engine drag at idle speed, the additional drag of Drive compared to Neutral (and therefore the resulting fuel savings in Neutral) would be extremely small -- certainly not enough to justify the safety issues caused by coasting in Neutral.
10-09-2013, 06:59 AM
#16
To the OP:
what you experienced in not normal. If I had to guess what occurred, I think the tranny must have either: (1) not entirely disengaged from the forward gear you were in, or (2) attempted to shift into another forward or reverse gear.
I would call my service rep and ask them to give it a check. At the very least they can look at the diagnostics and condition of the AT fluid.
In the end you likely did not do any serious damage, but having things checked may give you peace of mind.
what you experienced in not normal. If I had to guess what occurred, I think the tranny must have either: (1) not entirely disengaged from the forward gear you were in, or (2) attempted to shift into another forward or reverse gear.
I would call my service rep and ask them to give it a check. At the very least they can look at the diagnostics and condition of the AT fluid.
In the end you likely did not do any serious damage, but having things checked may give you peace of mind.
10-09-2013, 07:12 AM
#17
AudiWorld Super User
centurian, Perhaps you have a point however would "finite" fuel savings be more than a tenth of an ounce? Two tenths? If one could time it right coasting in neutral to a stop every time (a dubious assumption at best), I suspect the fuel savings over a year of stops wouldn't equal a gallon, especially since so much more time is spent idling while stopped anyway (unless the car is equipped with Stop/Start and engaged - a different topic entirely covered in several other forum threads). Coasting in neutral is not worthy of any consideration, especially due to the safety, additional brake wear and other considerations as you acknowledged.
The last( and only) time I ever coasted in neutral was years ago when I ran out of gas in my Jeep and was very fortunate to be able to coast down a hill into a gas station right up next to the pump. Needless to day, I have since avoided getting that close to empty.
The last( and only) time I ever coasted in neutral was years ago when I ran out of gas in my Jeep and was very fortunate to be able to coast down a hill into a gas station right up next to the pump. Needless to day, I have since avoided getting that close to empty.
10-09-2013, 09:16 AM
#18
centurian, Perhaps you have a point however would "finite" fuel savings be more than a tenth of an ounce? Two tenths? If one could time it right coasting in neutral to a stop every time (a dubious assumption at best), I suspect the fuel savings over a year of stops wouldn't equal a gallon, especially since so much more time is spent idling while stopped anyway (unless the car is equipped with Stop/Start and engaged - a different topic entirely covered in several other forum threads). Coasting in neutral is not worthy of any consideration, especially due to the safety, additional brake wear and other considerations as you acknowledged.
The last( and only) time I ever coasted in neutral was years ago when I ran out of gas in my Jeep and was very fortunate to be able to coast down a hill into a gas station right up next to the pump. Needless to day, I have since avoided getting that close to empty.
The last( and only) time I ever coasted in neutral was years ago when I ran out of gas in my Jeep and was very fortunate to be able to coast down a hill into a gas station right up next to the pump. Needless to day, I have since avoided getting that close to empty.
In the end, I think my message to the original poster is consistent with yours: In theory, I understand his or her motivation for coasting to a stop in neutral, but in practice the actual fuel savings, if any at all, would be so small they could not justify the increased safety risk.
Coincidentally, the only time I can recall coasting in neutral was similar to your experience. I was visiting a friend who lived on a farm. I ran out of gas just as I approached his driveway (a gravel lane that was close to 1/4 mile long). Fortunately, his driveway had a bit of a downward slope, and I coasted just far enough to reach the fuel tank my friend kept on the farm. Never again.
10-09-2013, 10:16 AM
#19
AudiWorld Member
Thread Starter
The point of coasting was not to save on fuel, but to avoid having to get on the gas (because I came up short) and then on the brake and so on. If done right, I believe you can save a little wear and tear. On my 2006 A3 with about 60k miles, I had plenty of life on the original rotors and brake pads.
10-09-2013, 10:49 AM
#20
AudiWorld Senior Member
