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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 November 29th, 2008, 22:11   #1
erinee88
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Default Really, really bad gas mileage

Hi all,
I've had my 2002 Golf TDI since Oct 2007. All along its gotten perfectly normal mileage... maybe 35-40 mpg. Its an automatic and i run 99% biodiesel. I try to minimize stop n go as much as possible and am pretty congizant of how to drive to maximize mileage.
Well, all of a sudden, the last 2 or so tanks, i've been getting about 22 mpg. Same gas, same driving style. I took it to Fine Tuning here in Seattle (very reputable, very trustworthy, and extremely smart about VWs) and they said they couldn't find anything wrong with it. Can anyone give me any advice? Thanks!
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Old November 30th, 2008, 15:26   #2
Smokerr
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Fuel Economy: 43.5/32/28
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I am sorry about your problem. Can't help, other than the usual fuel filter check, replacement, engine air filter and pull the EGR and take a look at the intake.

And, not to flame you, but you should refer to it as fuel mileage, not gas mileage. Diesel owners are very picky about the terms.
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Old November 30th, 2008, 18:47   #3
mynhare
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I had the same problem with my Jetta and it turned out to be pump timing. Took all of about 30 minutes to fix. Mileage went dramatically up. Hope this helps.
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Old November 30th, 2008, 19:02   #4
whitedog
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They may know VWs, but do they know TDIs as well as Matt at Zahntech in Redmond? If you are only getting 22 MPG, someting is wrong and Matt will find it.
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Old December 1st, 2008, 07:35   #5
MCathcart
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I know I can't help it. Gas? Did you say GAS? I normally get

1. 44 MPG (Gas) 1990 Festiva
2. 100 MPG (Gas) 2004 Honda Met
3. 50 MPG (Gas) 1998 HD, FLTRI

But I don't run gas in our diesels. (My wife tried it once.)
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Old December 1st, 2008, 07:39   #6
CentralFloridaTDIguy
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Quote:
Originally Posted by MCathcart
I know I can't help it. Gas? Did you say GAS? I normally get

1. 44 MPG (Gas) 1990 Festiva
2. 100 MPG (Gas) 2004 Honda Met {scooter}
3. 50 MPG (Gas) 1998 HD, FLTRI

But I don't run gas in our diesels. (My wife tried it once.)
I had to google and find out what it was.... added {scooter} for clarity
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Old December 1st, 2008, 07:48   #7
09tdiman
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Quote:
Originally Posted by Smokerr
I am sorry about your problem. Can't help, other than the usual fuel filter check, replacement, engine air filter and pull the EGR and take a look at the intake.

And, not to flame you, but you should refer to it as fuel mileage, not gas mileage. Diesel owners are very picky about the terms.
same with gas pedal
its the go pedal in diesel terms! i call it the diesel pedal
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Old December 1st, 2008, 15:13   #8
erinee88
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Thank you all! And oh wow - gas. Please forgive my newbie-ness. Much appreciated advice on both fronts!!
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Old December 1st, 2008, 16:34   #9
n1das
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Fuel Economy: Who cares? It's a DIESEL! Great fuel economy comes as a bonus!
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Quote:
Originally Posted by erinee88
Well, all of a sudden, the last 2 or so tanks, i've been getting about 22 mpg. Same gas, same driving style. I took it to Fine Tuning here in Seattle (very reputable, very trustworthy, and extremely smart about VWs) and they said they couldn't find anything wrong with it. Can anyone give me any advice? Thanks!
Maybe try DIESEL instead of GAS? My GAS mileage in my TDIs are always INIFINITE at all times since they use zero gasoline.

Maybe it's due to the switch to winterized fuel in your area. Winterized diesel has a few % less BTUs per gallon than summer fuel has and you'll notice it as a drop of a few MPGs. When you happen to notice the change it's always like a switch got flipped somewhere while nothing else has changed. IIRC, the amount of winterization and the date(s) the change is required to be made varies by region.

I live in NH and I've always noticed a 2-3 MPG drop around the middle to end of November and then a return to normal usually sometime around the end of April. My TDIs have 5-speed manuals. The MPG drop is just enough that I notice it but not enough to worry about.

Also what filling/topping off technique do you use when FUELing the car up? (Notice I said "fueling up" instead of "gassing up".) It's important to use the same topping off technique with every tank to get accurate and consistent MPG numbers. Either stop when the pump shuts off by itself and don't try to squeeze any more in or fully top it off all the way to liquid at the top of the filler neck. Whichever method you like to use, it's important that the same method be used EVERY time. With a diesel it's perfectly safe to fully top it off all the way to liquid at the top. You'll get your most accurate MPG numbers if you always fully top it off at every fillup.

Like others said, I suggest getting it to a TDIclub guru in your area who can check it out. I suspect the sudden drop is due to winterized fuel in your area.

Good luck and Welcome to TDIclub!
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Last edited by n1das; December 1st, 2008 at 16:38.
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Old December 3rd, 2008, 00:05   #10
sqhschief
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Quote:
Originally Posted by mynhare
I had the same problem with my Jetta and it turned out to be pump timing. Took all of about 30 minutes to fix. Mileage went dramatically up. Hope this helps.
How would one go about checking the timing?
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Old December 3rd, 2008, 06:16   #11
mrGutWrench
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Quote:
Originally Posted by erinee88
Thank you all! And oh wow - gas. Please forgive my newbie-ness.
__. Erin, we don't mean to be smarta$$es about this but if you tell people, "I don't think my gas mileage is good" and "I have to put gas in my car", the first time your brother-in-law borrows your car, he'll call about a block from the station saying "I filled it with gas for you but then the car stopped". It's just good practice to reinforce for yourself and everybody around you to say "diesel fuel" and think "diesel fuel" anytime you're talking about your car. Say "diesel fuel" to everyone, think "diesel fuel" to yourself and you'll go a long way toward improving your relationship with your car. It seems silly but it really helps.
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Old December 3rd, 2008, 06:23   #12
mrGutWrench
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__. Oh, yeah, one other thing. Diesel fuel is mixed with "other petroleum" to make it work properly in colder weather. Typically, people will lose 3-5 MPG with "winter fuel" but your MPG drop is obviously even more than this so I agree with everyone else -- get a very knowledgeable TDI diesel person* on this one for you. There's something wrong with your car but it can usually be fixed OK.

(*The guy down at the corner who calls himself "VW Motor Werks" has probably been in business for 22 years and is really good on VW car engines that run on gasoline. Your neighbors will tell you he costs a lot less than the dealer and does good work. That's probably true, but unless you know different, he's probably worked on three *diesels* in that 22 years. The TDI is different -- a mechanic who really knows them can make them purr, somebody who doesn't often blunders by treating them like gas-powered cars. Find the "VW Diesel mechanic" near you.)
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Old December 5th, 2008, 18:30   #13
2004STARWARSTDI
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Default Diesel vs Bio

You will get more MPG with diesel than BIO!
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Old December 8th, 2008, 11:45   #14
TornadoRed
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Quote:
Originally Posted by 2004STARWARSTDI
You will get more MPG with diesel than BIO!
Maybe even winterized diesel.

About Fine Tuning in Seattle. A quick search shows that they seem to have a good reputation with the TDI owners there. Zahntech is another recommended shop... it seems to have an even better reputation.
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Old December 14th, 2008, 01:45   #15
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Quote:
Originally Posted by sqhschief
How would one go about checking the timing?
Sorry for my noobieness I posted before searching, nevermind .
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