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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 December 28th, 2010, 09:38   #1
lostinatl
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Default 2nd tank 99.5 mk4 tdi

Well, my second fill-up ended up w/my mileage dropping to 37 mpg. After reviewing most of the post here, I realize that the fill-up definitely effects fuel economy. I am doing the vent removal today, but during fill up this time I kept pushing the vent and let the foam die down and I got in quite a bit more diesel. This most likely effected my mpg. I adjusted the tire inflation and now will start to hope for some type of realistic average, but will definitely start to focus on how much goes into the tank.
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Old December 28th, 2010, 16:25   #2
09R/T
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makes a huge difference.....even with the vent guts removed, i can still squeeze in another 1.5 gallons after the pump shuts itself off.....patience is key, mostly due to foaming.

I always fill to the brim, then i know i am never off by more than a few thousanths of a gallon.
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Old December 28th, 2010, 16:41   #3
85_305
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How much fuel you put in your tank will NOT affect mileage. They are unrelated. Just make sure you consistently fill it ALL the way up
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Old December 28th, 2010, 19:35   #4
09R/T
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Quote:
Originally Posted by 85_305 View Post
How much fuel you put in your tank will NOT affect mileage. They are unrelated. Just make sure you consistently fill it ALL the way up
It affects the perceived mileage of the vehicle, if you dont fill it the same everytime, then your perception may be that your mileage is much higher, or much lower than what the car is actually getting.
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Old December 28th, 2010, 19:45   #5
85_305
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Exactly. Perception isn't necessarily fact. He was saying that "After reviewing most of the post here, I realize that the fill-up definitely effects fuel economy" and "I am doing the vent removal today, but during fill up this time I kept pushing the vent and let the foam die down and I got in quite a bit more diesel. This most likely effected my mpg". The amount of fuel he puts in wont affect economy; but he DOES need to fill it up to the same point every time to keep accurate measurements of economy.
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Old December 29th, 2010, 04:03   #6
pnubble
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I've only had my TDI Jetta for three weeks and I went from 44MPG to 48MPG by just increasing the PSI in the tires. I'm looking forward to the first tank w/ 50MPG. By the way deisel in southern Maine is $3.489/gallon.
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Old December 29th, 2010, 07:21   #7
lostinatl
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Not sure how you can say that my fill up will not effect my mileage? If you use the basis: 400 miles / 15 gallons = 26.667 mpg
400 miles / 16 gallons = 25 mpg and 400 / 14 = 28.571

Unless you are checking your mileage a different way how much you put in will definitely effect your mileage. Or am I just missing something completely? I did do the vent, it took 5 minutes. Anyone who hasn't done it in the Atl area or is nervous, I can meet you and give you a hand. Just send a PM.
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Old December 29th, 2010, 08:30   #8
85_305
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Quote:
Originally Posted by lostinatl View Post
Not sure how you can say that my fill up will not effect my mileage? If you use the basis: 400 miles / 15 gallons = 26.667 mpg
400 miles / 16 gallons = 25 mpg and 400 / 14 = 28.571

Unless you are checking your mileage a different way how much you put in will definitely effect your mileage. Or am I just missing something completely? I did do the vent, it took 5 minutes. Anyone who hasn't done it in the Atl area or is nervous, I can meet you and give you a hand. Just send a PM.
Dude. It doesn't affect your damn mileage. If anything, more fuel will allow you to go FURTHER. But it wont 'affect your mileage'.

Why the f*ck would you keep going the same amount of miles while putting more fuel in? Thats asinine. How old are you? Because if your a kid I'll stop being an a$$hole but comeon seriously.. you wont be going the same amount of miles if you put more fuel in.

Your ideology of how fuel/distance work is all tangled up. The amount of distance you go is dependent upon how much fuel is available. The way your thinking is more will still equate to the same amount of miles traveled.
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Old December 29th, 2010, 11:39   #9
smck
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Take it easy on the new guy. I assume he is smart enough to know that his calculation was affected because he filled the tank more completely this time. Keep on it lost one you should easily be able to get 50's as should anyone with an alh manual.
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Old December 29th, 2010, 11:50   #10
IanMH
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I think I should be checking the air in my tires!
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Old December 30th, 2010, 07:04   #11
lostinatl
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Yea, your a genius 85 305. Do you understand how formulas work. It was an example. Genius.
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Old December 30th, 2010, 07:17   #12
85_305
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An example? Telling me that your economy is going to go down putting more fuel in, and that you will STILL only get 400 miles per tank even with more fuel, is ignorance. Not a formula.
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Old December 31st, 2010, 10:20   #13
raikky
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when i fill up i use the same station, the same pump every time usualy once per month. i just fill till it clicks. calculating my mpg 100 percent accuracy prob not. care? not really. you can get too obsessed with fuel economy. this venting thing sounds alright if i was filling up and the nearest pump from the one im filling up with is about 800 miles in which case id need the extra diesel. but thats about it
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Old December 31st, 2010, 13:57   #14
85_305
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It's nice being able to go an additional 120+ miles by venting my tank. Some people just like to refuel sooner :shrug:
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Old January 1st, 2011, 11:16   #15
flatlanded
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To be completely honest and neutral... you do get better fuel economy with an emptier tank due to the loss of weight. The results are negligible but still results none the less.

It is best to do economy calculations by filling up several times and using the average. One or two litres +/- on a fill up will make a difference from tank to tank basis.

37 is a little low unless you've been doing some stop and go city driving where accelerator is an on/off switch .
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