MPG vs. gliding in neutral

jessica_rabbit

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Hi All,
I am used to let the car coast/glide in neutral before stoping at a red light. The question is, is this good for the car since TDI are not suppose to idle much or is it worth it for the fuel saved? :confused:
Thanks!
Jess
 

PDJetta

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There was a thread about this ad naseum a while back. Pages and pages! Just do a search on it.

--Nate
 

Lightflyer1

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Round Rock, Texas
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2015 Beetle tdi dsg
When coasting out of gear at idle the engine uses very little fuel. When coasting in gear the engine uses no fuel. You must decide if you want to be in gear or out of gear depending on the circumstances. I coast in gear until the car slows to near idle speed, then shift out of gear if I still need to stop.
 

jessica_rabbit

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PDJetta: Will do.

Lightflyer1, bjmarler: Really? I didn't know coasting in gear uses no fuel. Even in 2nd or 3rd? Thanks guys.
 

whitedog

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jessica_rabbit said:
PDJetta: Will do.

Lightflyer1, bjmarler: Really? I didn't know coasting in gear uses no fuel. Even in 2nd or 3rd? Thanks guys.
When there is no accellerator pedal input and engine speed is above a certain speed, the VAG-COM will report that zero fuel is being injected.

There has been much debate about if there is actually zero fuel injected or if the amount is so small that the computer cannot report it.

BUT the computer can report the amount of fuel injected at an idle, so if there is any amount being injected in the over-run condition, it is less than at idle.

Then we find the argument that you won't coast as far in gear Vs in Neutral.

Also there are laws beyond the laws of physics to consider. Apparently it is illegal to coast in neutral in some or all places. Although the question is asked, "How would Johhny Law know?

I think those are the biggest agruments found here.

Me? I do a little of everything and leave the OCD fuel mileage numbers for others.
 

jessica_rabbit

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whitedog said:
When there is no accellerator pedal input and engine speed is above a certain speed, the VAG-COM will report that zero fuel is being injected.
How fast should the engine be running?
 

whitedog

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J, I don't really remember. It's around 1000 RPM +/- 100 I think. I want to say 950, but I may be wrong. It's in that general neighborhood.

Sheesh, you can't pin me down on saying anything there! LOL.
 

jessica_rabbit

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whitedog said:
J, I don't really remember. It's around 1000 RPM +/- 100 I think. I want to say 950, but I may be wrong. It's in that general neighborhood.

Sheesh, you can't pin me down on saying anything there! LOL.
Well, I suppose I have an eye for detail. Besides, I want to learn what I can for the car. :eek: Can't blame a girl for trying!

Jess
 

whitedog

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The info is here somewhere. If I found it important for me, I would remember it but like I said, I'm not really that concerned about the ultimate mileage and all of that, so those little details don't hold my attention too long.
 

jessica_rabbit

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whitedog said:
The info is here somewhere. If I found it important for me, I would remember it but like I said, I'm not really that concerned about the ultimate mileage and all of that, so those little details don't hold my attention too long.
I wouldn't be so concerned either if I didn't get 25 mpg on the last half of tank. :( But, thanks for the info.
 

daedalus

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I'm not so certain. I've been playing with coasting down grades over the past week or so. If I monitor the average MPG display while coasting out of gear it increases rapidly. Not so when coasting in gear (with TipTronic).
 

jessica_rabbit

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On a side note:

daedalus
: Do you have the Linux Journal Issue 121, May 2004, Titled: System Administration? If you do, look at Pg. 8 for the photo of the month. :D
 

rshelton

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Just curious as to how it all works when no fuel is being used. Is the transmission just turning the engine with the fuel pump shut off to keep it going?

Sorry, I'm still learning all about how the diesels work!
 

whitedog

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rshelton said:
Just curious as to how it all works when no fuel is being used. Is the transmission just turning the engine with the fuel pump shut off to keep it going?

Sorry, I'm still learning all about how the diesels work!
You have learned well grasshopper
 

daedalus

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jessica_rabbit said:
On a side note:

daedalus: Do you have the Linux Journal Issue 121, May 2004, Titled: System Administration? If you do, look at Pg. 8 for the photo of the month. :D
Nope - sure don't. Could you scan it for me?
 

meganuke

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VA/CT
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Allow me to attempt to simplify this argument. This is assuming the car has a manual transmission.

If throttle position = 0 and current_engine_speed > idle (803 rpm) then don't inject any fuel.

It doesn't matter what gear you're in or how fast you're going. As long as the rpms are above idle, and you're not requesting any fuel with the accelerator, then no fuel is injected.
 

BrianCT

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USA
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TDI
jessica_rabbit said:
Hi All,
I am used to let the car coast/glide in neutral before stoping at a red light. The question is, is this good for the car since TDI are not suppose to idle much or is it worth it for the fuel saved? :confused:
Thanks!
Jess
  • If you're capable of coasting in neutral before a stop-light or stop-sign you're capable of understanding acceleration vs. deceleration
  • If you're capable of understanding how much force is needed to get you rolling vs how much effort to stop that force you're on the Good Path
  • If you're easy on the acceleration on take-off and easy on the deceleration on slow down you save brake wear
  • If you're easy on deceleration you're also easy on the clutch throw-out bearings, tires and brake wear, the fuel consumption from saving fuel from excessive inertia
  • If you're capable of coming to a stop gradually you're also capable of saving huge amounts of money in wear-tear components attributed to ripping down speed to stops under "human rush" situations
  • Neutral to stops is cool
  • Judging the acceleration from take off to next stop is an art
 

coal_burner

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regenerative air conditioning

I downshift through all of the kears keeping RPMs at 1500-2000 with the air conditioning and fan on high, that way my forward velocity is being converted into cold air for my pass3nger compartment. once i'm stopped i switch the fan back down to medium. There are spots on my daily commute to work that i can coast in gear for almost a minute (so long as no one is right behind me to complain).
 

PDJetta

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coal_burner said:
I downshift through all of the kears keeping RPMs at 1500-2000 with the air conditioning and fan on high, that way my forward velocity is being converted into cold air for my pass3nger compartment. once i'm stopped i switch the fan back down to medium. There are spots on my daily commute to work that i can coast in gear for almost a minute (so long as no one is right behind me to complain).
Wow, I thought I was the only one that did this. Thanks, I feel better now!:)

--Nate
 

DavidG

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Southern NH
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None now
rshelton said:
Just curious as to how it all works when no fuel is being used. Is the transmission just turning the engine with the fuel pump shut off to keep it going?

Sorry, I'm still learning all about how the diesels work!
Just a big air pump!
 
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