# DRIVING in NEUTRAL: Gas



## Boile (Jul 5, 2005)

Ryan M said:


> It will be difficult to prove on paper or real world, simply because there are too many variables during a daily drive. Even if you go the same route for the same distance in the same direction and speed, results will still be skewed. So it won't be so simple as to just make 3 runs while using the "neutral" technique, and 3 runs in the "in gear" technique. If you figure out a way let me know, but I can't think of a way.
> 
> I just don't see how putting it in neutral can save gas over *decelerating in the highest gear*. I know the car will coast further in neutral, but it is still using enough gas to keep the motor running. Not to mention, if you are going freeway speed, say 70mph and your motor is turning 2500rpm, when you go to put it back into gear you will have to hit the throttle to match the revs before you can re-engage the gear.
> 
> I will be able to test this tomorrow. The car that I have had the last few days has an instant mpg readout that varies as you hit the gas. I know that upon deceleration in goes to 99mpg which is the highest readout it will give. I'm curious to see what it says in neutral. My guess is 0mpg, the same as at idle.


Why highest gear?
That shows me that you already suspect that descelerating in lower gears would be a waste of gas. 
If that's the case, the theoretical proof is very simple: induction.
Descelerating in 2nd gear is better than in 1st. 
Descelerating in 3rd gear is better than 2nd.
...
If you had infinite gears... your highest gear would be equivalent to neutral. 
QED. :thumbup::rofl:


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## cjwheeling (Jan 26, 2006)

Boile said:


> Why highest gear?
> That shows me that you already suspect that descelerating in lower gears would be a waste of gas.
> If that's the case, the theoretical proof is very simple: induction.
> Descelerating in 2nd gear is better than in 1st.
> ...


What if we turn the car off while driving down a hill, and maybe set up some type of regenerative braking setup and some batteries to save that wasted heat energy.


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## djfitter (Sep 12, 2007)

: popcorn:

dj


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## Ryan M (Dec 20, 2006)

Boile said:


> Why highest gear?
> That shows me that you already suspect that descelerating in lower gears would be a waste of gas.
> If that's the case, the theoretical proof is very simple: induction.
> Descelerating in 2nd gear is better than in 1st.
> ...


Okay. Let me try to clarify. I would select the highest gear because you will obviously coast longer in 6th than in 1st. 6th is a taller gear. But whether you are decelerating in 1st gear or 57th gear, you are still not using gas. So no, your highest gear is not equivalent to neutral. I don't know where you came up with that. Are we on the same page now?


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## cjwheeling (Jan 26, 2006)

djfitter said:


> : popcorn:
> 
> dj


Yeah, it is turning into a somewhat confrontational postfest. My bad, it's just so hard to resist sometimes.


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## Boile (Jul 5, 2005)

Ryan M said:


> Okay. Let me try to clarify. I would select the highest gear because you will obviously coast longer in 6th than in 1st. 6th is a taller gear. But whether you are decelerating in 1st gear or 57th gear, you are still not using gas. So no, your highest gear is not equivalent to neutral. I don't know where you came up with that. Are we on the same page now?


You're the one who mentioned descelerating in tallest gear.
Why don't you descelerate in 1st?
Obviously, coasting longer is the desired effect, if you want to save gas.
And neutral provides the longest coast.
And yes, if you want to save even more gas, turn the engine off.

Oh, and if you did have a 57th gear, coasting in it would use gas.
The computer sends gas to the injectors every time the rpm drops below 1000, which I think a 57th gear would do.
So it is exactly equivalent to neutral.


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## Ryan M (Dec 20, 2006)

Boile said:


> You're the one who mentioned descelerating in tallest gear.
> Why don't you descelerate in 1st?


Because 1st is shorter than 6th. You do realize that a taller gear has a lower numerical number, right?



Oh, and only because I know you'd do the same for me, there is no "s" in decelerate.


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## cjwheeling (Jan 26, 2006)

Ryan M said:


> Oh, and only because I know you'd do the same for me, there is no "s" in decelerate.


I'm joining djfitter: popcorn:


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## Boile (Jul 5, 2005)

Ryan M said:


> Because 1st is shorter than 6th. You do realize that a taller gear has a lower numerical number, right?
> 
> 
> 
> Oh, and only because I know you'd do the same for me, there is no "s" in decelerate.


I have an rule of thumb... when one of the parties start picking on typos, that's a clear sign that the argument is lost, so there's no longer a point in continuing. :rofl::thumbup:


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## cjwheeling (Jan 26, 2006)

Boile said:


> I have an rule of thumb... when one of the parties start picking on typos, that's a clear sign that the argument is lost, so there's no longer a point in continuing. :rofl::thumbup:


You spelled typo wrong.


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## Ryan M (Dec 20, 2006)

Boile said:


> I have an rule of thumb... when one of the parties start picking on typos, that's a clear sign that the argument is lost, so there's no longer a point in continuing. :rofl::thumbup:


Right, because you've never corrected someone on their spelling/grammar.


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## cwsqbm (Aug 4, 2004)

STL_John said:


> In any event, your car would be using so little fuel in either case that I can't imagine it would make much of a difference. I wonder how many gallons (fraction of a gallon) per hour an idling car consumes anyway.


Don't have the exact number, but if you watch the OBC, it makes a big difference in overall mileage to sit still at a light. Its a reason that idling trucks (bigger engine, but still they use a gallon/hour) are banned in many states now, and auxliary power units are becoming popular to run the A/C when the big engine is off.


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## Boile (Jul 5, 2005)

Ryan M said:


> Right, because you've never corrected someone on their spelling/grammar.


Yes, but only when I consider my point lost and I just want to post because I want to have the last word. :rofl:


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## 1985mb (Apr 2, 2008)

cjwheeling said:


> I don't believe that we specified a manual tranny? (or was that established and I missed it?)
> 
> I was thinking about an auto.


From what I understand, you should never do this in an auto, or any "manumatic" that has a torque convertor


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## Starab (Feb 17, 2007)

Boile said:


> In a manual transmission?
> Manual means you engage/disengage it.


I have auto trans. and I tried driving on NEUTRAL on exits from Interstates or steepdown road or coming to a stop and noticed my ACC disengages itself, rev drops to 1500- 2000, and this may save gas ??
I hope this does not damage my Mechanicals or Transmission(Steptronic)


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## Dammmittt (Jun 25, 2007)

If you read up on hypermiling...you don't just put the car in Neutral going down hill...you're supposed to turn it off. How serious are you about this?


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## klu123 (Nov 4, 2005)

Starab said:


> I read on this site that some people drive / switch their cars in NEUTRAL Gear:
> 1) on downhill
> 2) before approaching a stoplight
> 3) before coming to a complete stop.
> ...


Don't ever try it. it is dangerous! In the Drive mode, you use both the braking pads and the engine to brake, while in the Neutral mode, you depends only on the pads. The results are quite different in terms of braking distance. You could give it a try on a open roads.

It may save you a little bit of gas, but the risk is too high - accident and cost of reparing your car, not to mention the danger to you and others in your car.


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## Synaps3 (Mar 3, 2008)

Thread summed up:



Boile said:


> Post #1 was pretty clear to me.
> But in case you missed it, re-read post #12.
> And my post, which you quoted, was in response to post #18. Only manuals have a clutch, no?


Both auto/manual have a clutch. Auto just does the clutch work for the driver. It's still there.



Starab said:


> I read on this site that some people drive / switch their cars in NEUTRAL Gear:
> 1) on downhill
> 2) before approaching a stoplight
> 3) before coming to a complete stop.
> ...


0) Hypermiling tends to refer to manual transmission cars, traditionally, as many of the techniques were originally used during WWII as a result of fuel rationing. (Wikipedia) However the "neutral" in an auto transmission should be analgous to its cousin in manual.

1) On a downhill, coasting in your highest gear is superior to coasting with the engine disconnected (in neutral/with clutch in). In gear while going downhill, the engine turns because the wheels are turning, and no fuel is needed to flow to it. When disconnected from the wheels (neutral) the engine needs a trickle of fuel to burn in the cylinders to prevent the engine from stopping.

2) When approching a stoplight, from a fuel perspective, it depends on the distance from the light. From a fuel perspective, the best option is to "time the light" so that when you arrive it has become green again, and you don't need to stop. Ideally this would mean coasting in the highest gear possible, but not so high that you dont lose enough speed and the light hasnt changed when you get to it. Again, letting the wheels turn the engine with no gas is better than neutral (equivalent to idle) which needs gas. Also remember that frequent shifting coming up to a light results in higher clutch wear, and a clutch replacement will cost more than your savings in gas most likely. Best option? let off on the gas in your current gear and try to time the light so youre still moving, and its green when you get there.

3) Switching to neutral will cause more fuel consumption than coasting to a stop in your current gear. Downshifting to stop causes clutch wear instead of brake wear(....replace your brakepads not your clutch..dumb idea...)

4) Idling on an average sedan costs you 17% of your fuel in city driving, and 4% in average highway driving. I'm sure hypermiling behavours, especially pulse/glide and coasting on the highway, would make that number go up. So fuel loss to idling is significant.

5) From a fuel economy standpoint, about 10 seconds of gas(in neutral) is what it costs you to start your engine. So the hypermilers rule of thumb is it's more efficient to turn off the engine if you won't be pressing the gas again in more than 10 seconds. This is dangerous, possibly harmful to your car, and in some cases ILLEGAL, depending on location and car design. In some cars the transmission lubricant circulation is managed by a pump powered by the engine, so your trans could lock up...that would be fun. Turning off the engine also means you lose anti-lock brakes, and power steering. Make your own call on that but the consensus seems to be that at some point, fuel vs safety comes seriously into play. IE drafting behind a semi-trailer at 3 feet with engine off, no ABS pressure, no power steering....at some point its worth using the gas to have those features. In short there's a reason its called an "advanced technique"

Other answers can be found in the wikipedia article on hypermiling
http://en.wikipedia.org/wiki/Hypermiler


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## Boile (Jul 5, 2005)

Synaps3 said:


> Both auto/manual have a clutch. Auto just does the clutch work for the driver. It's still there.


Wrong.


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## Ryan M (Dec 20, 2006)

Synaps3 said:


> Both auto/manual have a clutch. Auto just does the clutch work for the driver. It's still there.


Please post a pic of this so called clutch in an auto.


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## Synaps3 (Mar 3, 2008)

Huh...k...how does the car manage partial power to the wheels then? When starting from a stop, the wheels wouldnt be turning fast enough to keep the engine from stalling. Something's gotta slip so that the engine doesnt stall if the wheels arent turning fast enough. That something is a clutch.

EDIT: Hmm Torque Converter eh? Good catch guys. Seems I was wrong. The beginning of the wikipedia article on clutch said that "A clutch is a mechanism for transmitting rotation, which can be engaged and disengaged." in which case an auto transmission would have to have a "clutch". I guess a torque converter is not considered one, and the "clutch" definition is more exact than the wiki gives.

http://en.wikipedia.org/wiki/Torque_converter

DOUBLE EDIT: HAHAHAHAHA I win. "As described above, pumping losses within the torque converter reduce efficiency and generate waste heat. In modern automotive applications, this problem is commonly avoided by use of a lock-up clutch that physically links the pump and turbine, effectively changing the converter into a purely mechanical coupling. The result is no slippage, and therefore virtually no power loss."

HERES YOUR IMAGE: #2 is your "Torque converter lock-up clutch with damping elements "








Source: http://www.daimler.com/dccom/0-5-1059924-1-1063782-1-0-0-0-0-0-14972-0-0-0-0-0-0-0-0.html "The 7G-TRONIC automatic transmission"

I win.


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## captainaudio (Jul 17, 2007)

Ryan M said:


> Please post a pic of this so called clutch in an auto.


The Steptonic is a true automatic and has a torque converter (no clutch) although it is locked up most of the time.
The SMG has a (computer controlled) clutch.

Mecedes has just introduced an automatic that has a clutch instead of a torque convertor.


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## captainaudio (Jul 17, 2007)

Synaps3 said:


> Huh...k...how does the car manage partial power to the wheels then? When starting from a stop, the wheels wouldnt be turning fast enough to keep the engine from stalling. Something's gotta slip so that the engine doesnt stall if the wheels arent turning fast enough. That something is a clutch.


Actually it is a fluid coupling called a torque convertor.


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## Ryan M (Dec 20, 2006)

captainaudio said:


> The Steptonic is a true automatic and has a torque converter (no clutch) although it is locked up most of the time.
> The SMG has a (computer controlled) clutch.
> 
> Mecedes has just introduced an automatic that has a clutch instead of a torque convertor.


Yes, I realize that.


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## Ryan M (Dec 20, 2006)

Synaps3 said:


> Huh...k...how does the car manage partial power to the wheels then? When starting from a stop, the wheels wouldnt be turning fast enough to keep the engine from stalling. Something's gotta slip so that the engine doesnt stall if the wheels arent turning fast enough. That something is a clutch.
> 
> EDIT: Hmm Torque Converter eh? Good catch guys. Seems I was wrong.
> 
> http://en.wikipedia.org/wiki/Torque_converter


If you are referring to clutch plates, which an auto has, they're not the same as a clutch disk in a manual.

Edit: nevermind, I see you corrected yourself.


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## Synaps3 (Mar 3, 2008)

I think I win. I found a clutch in an auto transmission AND posted a cutaway image of it. It's even from a german manufacturer.

Pure win, baby.


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## TMQ (Jun 3, 2004)

1. Going downhill in neutral is dangerous. You can't drive if something dangerous occurs.

2. Coming to a red light, it's fine to shift to neutral - say you are in 3rd gear and see the light, brake the car and the rpm drops to about 1k rpm, there's no need to change to second gear - shift to neutral and let the car brake to a stop. If the light changes to green before you stop, you can shift to 2nd gear and keep moving. 

3. Stopping at the light, leave the car in neutral is good - less wear on the clutch.


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## AndrewZ (Feb 1, 2006)

I gave this Gas-Saving method a try for the past week. I tried this on my 95 Accord EX Automatic. Turning the car off at long stop lights, coasting in neutral, not using the A/C, going the speed limit on streets and freeways ( sorry to the people I pissed off going the speed limit :fingers all rounded up to 27-30 mpg's from the average 20-23 mpg's I normally get on it. 

Hardly worth the effort and I can't help but to think about the wear and tear on the starter and transmission.


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## Pinecone (Apr 3, 2002)

1) Modern automatic have a clutch, that locks and bypasses the torque converter when you are cruising. This heps gas mileage by eliminating the slip of an automatic tranny.

2) Neutral at stopslight should burn slightly more gas than clutch in. The reason being, in neutral with clutch pedal out, you are turning all the gears in the tranny and you are churning the oil, which takes power. Clutch in, you are only dealing with the drag of the throwout bearing.

3) The shutting down at stop ligfhts, IMO, doesn't seem to take into account the electrical engery required to recharge the battery from the start. But I may, I have not gone into it that deeply.


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## bmwboss (Apr 21, 2008)

my friend told me about this mith before and ive tried it a few times shifting into nuetral at every downhill or other opertunity and if it helped it helped very little i still do it out of habbit occasionally but the best way to save gas is avoid accelerating like its a race when you are simply driving to work


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