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My first TDI MPG update (400 mile trip)

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Old 04-29-2014, 06:58 AM
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Default My first TDI MPG update (400 mile trip)

Hi All,

During the winter, I was getting about an average of 26 MPG (city/highway) with a roof rack. On my snowboarding trips, I would only average about 28 MPG (highway) with the roofrack and snowboards/skis on there.

Now that the weather is warmer and after i removed my roof rack, I am happy to say I've broken my personal record during my roundtrip from NYC to Boston and gotten 32.6 MPG on the highway.



(its just a pic of my dashboard showing my 32.6 mpg average)
Old 04-29-2014, 10:29 AM
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Using the dash computer to tell your mileage is inaccurate. calculate it by using the miles driven over the amount of fuel used. calculate during the fillup. it will be far more accurate.
Old 04-29-2014, 05:25 PM
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Then why does Audi spend tens of thousands of dollars to develop the MPG system computers. I have always found mine to be accurate with a half a mile or so. Sometimes spot on.
Old 04-29-2014, 05:26 PM
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Took a recent trip from IN to FL with my '14 Q5 TDI. Cruise set at 75 all the way. Saw 37.9 mpg on my trip computer when I stopped in TN to fill-up. Was overjoyed to say the least until I calculated using simple math and the fuel receipt to find I actually got 34.3 mpg. Still, it exceeds the EPA rating by quite a bit and, at a decent speed so I guess I'm still happy. If there is a disappointment, it's in the 10% error on the digital gauge, which to me is extreme. My previous five cars were never off by more than a couple tenths of an mpg.
Old 04-29-2014, 05:38 PM
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my experience is that the computer is optimistic by 2-3mpg. The other thing I notice is that the gas gauge is VERY slow to come off of "F" and I can often get about 300 miles around town before it gets to 1/2 tank. Then it goes down much more quickly during the second 1/2 tank. Both of these "tricks" are designed to accentuate the MPG's you are getting by giving you the feeling that the car is getting better mileage than you really are. Don't get me wrong--the car still does great in terms of fuel economy. It's just not as good as the gauges make you think.
Old 04-29-2014, 06:11 PM
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Originally Posted by mhughett
my experience is that the computer is optimistic by 2-3mpg. The other thing I notice is that the gas gauge is VERY slow to come off of "F" and I can often get about 300 miles around town before it gets to 1/2 tank. Then it goes down much more quickly during the second 1/2 tank. Both of these "tricks" are designed to accentuate the MPG's you are getting by giving you the feeling that the car is getting better mileage than you really are. Don't get me wrong--the car still does great in terms of fuel economy. It's just not as good as the gauges make you think.
It bothers me that Audi would resort to these blatant 'tricks', and I'm sure that it's intentional. Spending 50k on an automobile, I'm buying into what I perceive to be advanced engineering, leading edge technology and superlative design. Then they hit you with a cheap stunt like the mileage meter. It disrespects their client base.
Old 04-29-2014, 07:33 PM
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My wife and I just returned from a New England road trip in our new TDI. We traveled from Boston to Maine, back down and around through New Hampshire into Vermont, and then home again. I would estimate that I averaged 70+ MPH. After filling up, I calculated MPG and was thrilled to learn that I averaged 31.28 MPG. That is excellent considering my old A4 Quattro 1.8 averaged around 25 MPG on long trips.
Old 04-30-2014, 07:08 AM
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Originally Posted by indyrich
Took a recent trip from IN to FL with my '14 Q5 TDI. Cruise set at 75 all the way. Saw 37.9 mpg on my trip computer when I stopped in TN to fill-up. Was overjoyed to say the least until I calculated using simple math and the fuel receipt to find I actually got 34.3 mpg. Still, it exceeds the EPA rating by quite a bit and, at a decent speed so I guess I'm still happy. If there is a disappointment, it's in the 10% error on the digital gauge, which to me is extreme. My previous five cars were never off by more than a couple tenths of an mpg.
7-8% seems a little more common. Still more than my 2002 Passat from what I recall (but it also got ~20mpg so a full 10% would be 2mpg off), but much better than my 2009 Odyssey which could be +-20% instead of the more-constant +8% consumption that I'm seeing on my TDI. You can easily get the computer to show a more-accurate (for you) value here, but in the case of my Odyssey even if it was possible to give the computer an offset the values were basically "random" so you never had a chance of guesstimating how you were doing.

Originally Posted by mhughett
my experience is that the computer is optimistic by 2-3mpg. The other thing I notice is that the gas gauge is VERY slow to come off of "F" and I can often get about 300 miles around town before it gets to 1/2 tank. Then it goes down much more quickly during the second 1/2 tank. Both of these "tricks" are designed to accentuate the MPG's you are getting by giving you the feeling that the car is getting better mileage than you really are. Don't get me wrong--the car still does great in terms of fuel economy. It's just not as good as the gauges make you think.
Most cars seem to stay with the needle on F for a while. Just as "E" doesn't mean the tank is completely dry, "F" doesn't mean that the tank is completely filled, but rather that the level is such that you could be considered to have a "full" or "empty" tank (you're good to go for a while, or you should really fill up soon). People exploit this in rentals all the time, where they only fill up the tank to where the needle just hits F rather than until the pump shuts off (tank is "full" full).

What I've noticed is that it takes me right around 100mi for each marked 1/4 (F -> 3/4, 3/4 -> 1/2, 1/2 -> 1/4), as well as 50mi for 1/4 -> 1/8, so the needle's "speed" is very constant (given constant fuel consumption, of course). It takes right around 100mi for the needle to move off F, which means that effectively "F" designates 80%+, which seems reasonable enough to me. I didn't bother checking in any of my other vehicles how long they'd stay on F, just here since there's a lot of people complaining, so I can't say if they were 80% as well or 90% or 75% or what.
Old 04-30-2014, 08:27 AM
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Originally Posted by indyrich
It bothers me that Audi would resort to these blatant 'tricks', and I'm sure that it's intentional. Spending 50k on an automobile, I'm buying into what I perceive to be advanced engineering, leading edge technology and superlative design. Then they hit you with a cheap stunt like the mileage meter. It disrespects their client base.
I doubt that it is intentional. It is just the way it is measured isn't most accurate way to measure it. I've never had a car where it was always right. It gives you an idea of what you are getting but if you want to know for sure, you should calculate it during fill ups and store it on fuelly. Probably the most accurate way is to weight the fuel before and after driving. But that is a little hard to do unless you modify the car.
Old 04-30-2014, 09:14 AM
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If you have a VAG/COM cable, you can adjust the calculation factor from the standard 100 to 108.

AFAIK the factor of 108 is the most accrue. It matches my hand calculation with a margin of error in less than 3%.

I'm getting a combined of 29-30. City 22-25, highway (around 70 mph) 32-35.


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