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TDI Fuel Economy Discussions about increasing the fuel economy of your TDI engine. Non TDI related postings will be moved or removed.

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Old May 12th, 2004, 08:59   #1
amorfeusz
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Join Date: Nov 2003
Location: Chicago,IL
Default Fuel Consumption - City Driving AUTO vs MANUAL

Just hooked up my Jetta 03 Wagon Automatic to a VAG-Com and noticed the following :

Fuel Consumption when idling in Drive - ~1.2 l/h
Fuel Consumption when idling in Neutral/Park - ~.7 l/h (sometimes .6l/h)

that's ~40% less fuel being used when sitting at stoplights/heavy traffic when in Neutral...

Now from what I know about manual, when you're not driving you're basically in Neutral right? So ppl with a manual transmission use 40% less fuel when sitting there in traffic as compared to Automatics who sit around in 'Drive'?

Can anyone with a manual and VAG-Com confirm this?

I know a lot of other factors play into a manual being more efficient than an automatic , but at least for city driving this would seem to be a big one. I'm going to start standing around in Neutral from now on to compare. Once I get my VAG-Scope MOD calibrated I'll do some test runs to see how this change affects economy.

P.S. also just saw how A/C affects fuel consumption - OUCH!
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Old May 12th, 2004, 09:19   #2
alex wetmore
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Join Date: Apr 2002
Location: seattle, wa
Fuel Economy: 35-40mpg average city driving
Default Fuel Consumption - City Driving AUTO vs MANUAL

[ QUOTE ]
Just hooked up my Jetta 03 Wagon Automatic to a VAG-Com and noticed the following :

Fuel Consumption when idling in Drive - ~1.2 l/h
Fuel Consumption when idling in Neutral/Park - ~.7 l/h (sometimes .6l/h)

that's ~40% less fuel being used when sitting at stoplights/heavy traffic when in Neutral...

Now from what I know about manual, when you're not driving you're basically in Neutral right? So ppl with a manual transmission use 40% less fuel when sitting there in traffic as compared to Automatics who sit around in 'Drive'?

Can anyone with a manual and VAG-Com confirm this?


[/ QUOTE ]

Yes, this is true.


[ QUOTE ]

I know a lot of other factors play into a manual being more efficient than an automatic , but at least for city driving this would seem to be a big one. I'm going to start standing around in Neutral from now on to compare. Once I get my VAG-Scope MOD calibrated I'll do some test runs to see how this change affects economy.


[/ QUOTE ]

In most cases I don't think that this will make a big difference. Using twice of a small amount of fuel for what is a short time on most drives isn't going to make a big impact on fuel economy. I'm guessing 1-2mpg at most.

This of it this way. In a typical hour of city driving you might be idling for 10 minutes at stop lights (I don't consider shifting to neutral to be useful at stop signs, because you are there for so little time). That is .2 L of fuel in Drive, or .11 L of fuel in Neutral. Converted to gallons that is .052 gallons vs .029 gallons. At 35mpg (typical for the automatic) that would get you 35 * (.052 - .029) an increase of .8mpg. That isn't nothing, but it isn't a huge increase.

The best reason to shift into neutral is that it makes the car much quieter. Automatic TDIs feel much louder than manual ones to me largely because they are so much louder at idle. I think that they are louder while driving too, presumably due to the higher pressure pump.

I don't necessarily expect useful answers from them, but my wife and I keep meaning to call Car Talk because we enjoy listening to it and this will come up as a husband/wife issue. I want to ask them about wear on the automatic transmission from two activities:
* shifting to neutral to idle
* parking the car and turning it off before putting the transmission into park. I always forget to do this because I'm used to parking my manual TDI where the transmission is already in 1st or Reverse by the time I'm done parallel parking and I don't need to do anything else with it.

alex
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Old May 12th, 2004, 18:17   #3
TDA
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Join Date: Oct 2002
Location: Hamilton, Ontario
Default Fuel Consumption - City Driving AUTO vs MANUAL

I always throw it into neutral at a traffic light. With 50/50 driving, I can't say I've noticed an increase in my economy. I don't track it that closely. The decrease in cabin noise and vibration is most welcome. We waste the most energy slipping the torque converter on acceleration. Kerma is working on a new torque converter that should address this, even if it's main objective is putting more power to the ground.
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