drop in mileage. Why?

[Andrewh]

2006 jetta. I have 9k miles on it now. Bought it last july. I started out with the crappy 30mpg then it slowly started to climb to 36 almost 37 mpg.
About a month or two ago, I took it into the dealer to have them fix a dash rattle and the speedo off set. When I got it back, I thought they had fixed the speedo, which I recall causes a problem with the odometer. So I started seeing 32 mpg. Same driving, but maybe a switch to summer blend?
Anyway, I finally got to take a road trip, and found that the speedo was still off, and the odometer was still dead on.
So what gives?
Why would mileage drop over 10 percent. Best mileage I got on the whole road trip was 35mpg.

 

[TDIPirate]

Uhmm, Is your jetta a gasser, because a tdi (diesel) should be getting mpg averages in the low 40's. If its a gasser, your in the wrong forum, but I'm sure someone will be glad to help, and if you have a TDI then you have something very wrong.

 

[bmwM5power]

Uhmm, Is your jetta a gasser, because a tdi (diesel) should be getting mpg averages in the low 40's. If its a gasser, your in the wrong forum, but I'm sure someone will be glad to help, and if you have a TDI then you have something very wrong.

of course it is a diesel. No gasser starts form 30mpg and then climb to 37-38mpg. Andrewh, how do you check your MPGs, by what computer tells you or by old fashioned way? I suggest filling the car up, record how many gallons you put in, and then wait till you out of the fuel and divide the mialege by the gallons, If there is something wrong with your cauges cluster the MPG reading off the computer maybe wrong.

 

[Andrewh]

The old fashioned way. I use the trip odometer and reset it everytime I fill up.
And yes it is a tdi.
I checked and the odometer and trip ometer are both tracking correctly.
I go about 440 miles between fill ups. That is about 14 gallons. But this only happened after they said they ripped out the dash to fix the buzz. Doesn't seem like it could be related, but wanted to get all the facts out.
I might have changed where I get my disel at the same time, but would have to look back at my reciepts to be sure. Krogers near me started to carry it, and it was cheaper there by 10 cents or so. Only one tank not by them recently and that was a flying j on my trip to galvaston.

Btw, that is all city driving.

 

[mmalluck]

30 Mpg does seem a little low. What does your daily commute look like?

I ask because this makes a big difference in fuel efficency as well as your driving style. I know with my driving I can see as low as 32mpg. That's with a daily commute of 20 miles round trip, 50% freeway @ 75mph and %50 city. I always take it up to 3000 rpms between shifts. Most of my cruising is around 2200 rpms.

With typical freeway trip-travel (set the cruise at 75 and go) I see around 42 mpg. If I keep it to 65mpg I'll squeeze out 48mpg.

My lifetime average is sitting around 38mpg after 30k miles.

Tire inflation can also make a difference. Higher pressure usually means higher mpgs (less rolling resistance as less rubber contacts the road). I keep my tires around 40psi.

Temperature also plays a roll. Higher temp makes for a less efficent engine and may also mean your running the air conditioning costing you preceious MPGs. I live in the friggen swamp (Savannah, Ga) so my AC is always on. It's been in the ninties since april. Humidity is around 90% all year.

 

[mtbr297]

fuel economy

2006 jetta. I have 9k miles on it now. Bought it last july. I started out with the crappy 30mpg then it slowly started to climb to 36 almost 37 mpg.
About a month or two ago, I took it into the dealer to have them fix a dash rattle and the speedo off set. When I got it back, I thought they had fixed the speedo, which I recall causes a problem with the odometer. So I started seeing 32 mpg. Same driving, but maybe a switch to summer blend?
Anyway, I finally got to take a road trip, and found that the speedo was still off, and the odometer was still dead on.
So what gives?
Why would mileage drop over 10 percent. Best mileage I got on the whole road trip was 35mpg.

I know of someone with a similar problem. He took it to dealer and he fuel economy went down. He had the same complaint. I use the vagcom to check his odometer and speedometer. The odometer was accurate but the speedo was off. At 70mph vagcom showed about 107kph. It should have should 112kph. 107kph is about 66.5mph. Still not sure what the problem is.
Steve

 

[Andrewh]

Well, my commute hasn't changed. All at around 40-50 mph, about 9 miles each way. Takes about 30 min to drive. I floor it when I can, and putter when I can't.
The speedo is about 5 mph off. Shows 70 when doing 65mph according to the unmanned radar traps, and about 3 mph slower by gps.
I haven't done anything different so I was wondering what else it could be.
No power loss as far as I can tell, but I thought it might be a bad fuel filter, but I haven't even hit 10k yet.
Thought it might be a bad batch of disel, or summer blend? but the batch from the flying j didn't improve mileage much.
Also I am in Texas, so I run A/C all year round pretty much except January maybe.

 

[Lightflyer1]

I would start by checking the value with Vag-Com to make sure the TSB wasn't done. I know you said you checked it, but with Vag-Com you can actually see if it was changed to something else for a value. The odometer being off could be the cause of your problems. Especially if nothing else has changed as you said.

 

[Andrewh]

Where do you check? Or a link would be fine, as I have the Vag-com stuff.
I can't believe it is off though. I checked with mile markers on the highway. Multiple times. They were spot on.

 

[wldwsel]

I had the same complaint about this time last year (I had around 10000 Miles on the car). I've kept an Excell sheet on every tank that has gone into my TDI. Average mileage is 39.58 MPG over 23000 miles.

Having said that, my LAST tank(today) was 37.45 MPG. My mileage has steadily eroded since the weather became warmer, an opposite of last Fall when it went steadily up. I run the AC all year, but maybe it has to pull more horses when it's hot outside. My car did the same thing last year, although the milage this year is 2 MPG higher, I'm pretty sure to break in. It's pretty neat to see the Excell graph - it's a sine wave for sure - two cycles so far.

If I'm right, about the middle of September, it will go over 40MPG again, topping out around 43MPG in February. I expect the overall milage to stay about where it is (39-40), and I love this little car!

 

[wldwsel]

PS - I verify all of my miles and speeds with a Garmin Nuvi.

 

[Jettageek1962]

Mpg

Andrewh I have 39,500 miles on my 2006 TDI PK 1. I average 43 MPG. Highest tank ever was 47 MPG and lowest tank ever was 38 MPG.

I don't know what to tell you about your lower than expected mileage, but you brought up something that got my interest. You explained that they took your dashboard apart to fix something, perhaps a rattle.

What exactly did they do to fix it? My TDI has a strange rattle but my dealer did not want to get into the dashboard to fix it. I'd like some information to give my dealer about the possible source in the dashboard.

 

[mmalluck]

Something to remember about the air conditioner: Unlike many conventional cars, our air conditioner works on a "as-needed" bases. Once the cabin reaches the dialed-in temp, the compressor kicks off until it's needed again. In winter heat is applied until the correct temperature is met. This means you can set the temperature dial in the car and leave it there year round. The system is smart enough to give you heating or cooling.

Many cheap american cars just leave the compressor running at a duty cycle determined by the "temperature dial". There is no temperature input into the system, so if it's 120 degrees or 32 degrees, the compressor runs for the same duration, given the same dial setting. In these cars you always have to tweak the dial from summer to winter to get a comfortable cabin temperature.

For our cars, higher outside temperatures mean a higher duty cycle for our air conditioners, which in turn means lower fuel milage. On the upside summer to winter my airconditior/heater stays set at 72 degrees.

 

[Andrewh]

Jettageek1962- They said they added extra sound deadener. Had to take the whole dash out of the car to do it. So they claim. I don't know if they did that or just used that as an excuse for why they didn't give it back to me on time.

mmalluck- actually that is not true about other cars. All new cars use the new compressor type. They are all as needed. The clutch stays engaged, but does not mean the compressor is under load at all times. Even the retro kit I installed on my old dodge has that.

 

[TDIPirate]

Thats why I thought that maybe it was a gasser, Since I've had mine, I've done about 40% city driving and 60% hwy, I drive it like I stole it , and The lowest mpgs I've seen by long hand was 39 and a half. And that was when it had less then 5 k on it and winter fuel. I'm interested in this too because i have a very slight rattle too just behind the dash.

 

[Andrewh]

mine was pretty consistent. You could hold rpm at 1800 and hear it all day long.
I kept hearing it driving, then sat and ran through the rpm ranges till I got it to hit constintly.

I guess the dealer will blow it off as regular mileage variations then?
Almost up on my year.

 

[Vipervnm]

Jettageek1962- They said they added extra sound deadener. Had to take the whole dash out of the car to do it. So they claim. I don't know if they did that or just used that as an excuse for why they didn't give it back to me on time.

mmalluck- actually that is not true about other cars. All new cars use the new compressor type. They are all as needed. The clutch stays engaged, but does not mean the compressor is under load at all times. Even the retro kit I installed on my old dodge has that.

Yup, so did my Beretta despite the piece of junk that it was. And no, my Jetta does not know to turn the AC on by itself. If the button is off it stays off. Also, I'm fairly certain it doesn't have a clue when the cabin has reached the proper temperature. It just keeps getting colder and colder...

 

[no-blue-screen]

Something to check is your brakes....are they dragging? After you clean the car...do you notice that one wheel builds up more brake dust than the others? There have been numerous cases of dragging brakes on the A5 cars and I am sure that doesn't help fuel economy at all. Another thing you have to remember is that when you idle you are getting 0 MPG....so if your commute involves long periods of idling and not moving then you will see lower numbers when you do your calculations. It's just not a good idea to idle your car....the only time I do it is for like a min or so after I get off the freeway in hot weather....to let the turbo cool down. My worst average was 41 mpg over a tank. Also, summer blend should improve your fuel economy not reduce it. Winter diesel is blended (usually 20/80 with #1 diesel which only contains about 50% of the energy of #2 diesel) to reduce the gel temp so the winter time (in cold areas) is when you will see a reduction in fuel economy.

 

[Andrewh]

Brakes seem to be fine. No build up on any of the wheels.
I did notice today the black soot is a bit more noticible on the rear of my car. Hadn't seen a build up before.
I don't idle the car much at all. Regular driving is has me sitting at lights for a little while. No more than 5 min at any one light. But as I said, my commute has not changed.
If it isn't the fuel, then something else must have gone wrong.

 

[LF06VWJTDI]

Today a friend at work pops in and tells me he got 735 freaking miles on one tank. 48.6MPG!!!!!!!!!!!!!!!!!!!!!!!!
I almost told him to f... off!

I've been averaging about 34 lately. My damn A/C cuts about 8MPG's

 

[Vipervnm]

Today a friend at work pops in and tells me he got 735 freaking miles on one tank. 48.6MPG!!!!!!!!!!!!!!!!!!!!!!!!
I almost told him to f... off!

I've been averaging about 34 lately. My damn A/C cuts about 8MPG's

I know how you feel. I've been gunning for the 700 club for a while now and can't quite get there. It may be due in part to the fact that I can't resist a good flogging of the engine every now and then. Why else would I have gotten chipped?

 

[LF06VWJTDI]

I know how you feel. I've been gunning for the 700 club for a while now and can't quite get there. It may be due in part to the fact that I can't resist a good flogging of the engine every now and then. Why else would I have gotten chipped?

I have no chances at all. My highest mileage on a full tank was 633 miles.
At least you've been gunning the 700 club..., while flogging your engine.
Me, with the mileage I get I can flog my bishop (fortunately I don't belong to the L.A. archdioceses ) while gunning my cojones...

 

[Lightflyer1]

You just need a 400 mile trip and some time. You too can be in the exalted high 700/800 mile club. Only benefit is the story you can tell about how you sat in the car for 17 hours or so. My wife hates that part. Trips are now about bladder control and not when to stop for fuel!

 

[chummer]

hahaha, i hear you on that Lightflyer1.

 

[Guttboy]

Lightflyer....hit the elusive 800mpg club on my last trip!!!!!!!!!!!!!!!!!!!!!!

Sorry Off topic

 

[Joshua]

Our best average was 45 mpg, and that was going from NC to FL. Average at home is 33.5. 40-ish on the way to work, 20ish on the way home (different routes).

 

[inveSTigator]

Wow, I'm a little surprised by the diff. in mileage by members. I have a new 06.5 DSG and currently have 4300 miles on it. I am following DBW's recomm. break in procedure. I am not running any additives of any kind. I have used Sam's Club ULSD exclusively since new. My commute is 55 miles round trip with 75% hwy/ 25% City with small hills. I typically drive 82mph hwy and approx. 6mph over posted everywhere else when it is safe to do so. I'm usually (easily) the first car off the light.
My MFD is spot on, verified by hand calculation, though I think my speedo may be off a bit. The lowest I've seen on short trips is 38mpg and my highest was 51mpg.
I have checked the oil reguarly and have not used any thus far.
I have been averaging between 40mpg and 43.5mpg per fill up and my best so far is 627 miles on 14.4 gallons. I noticed a very sudden 3mpg jump at 3700 miles. I can't wait till she's broken in!!!!

 

[LF06VWJTDI]

I got the flaming suit already on but I must say this:

DBW's instructions for breaking in DO NOT apply to DSG-equipped vehicles.
The transmission's own internal software already shifts at appropriate RPM points and applying the "drive-it-like-you-stole-it" instructions by DBW will only put extra wear on the transmission, which, itself needs to be broken in.

Trust me and if you want to drive aggressively while you break in the engine just drive in S mode. You don't want to end up with your new vehicle parked for a couple of two three months at the dealership's while your dual-mass flywheel is being shipped from Germany.

 

[inveSTigator]

I don't feel like the autobox does shift at optimal points with normal driving. If I leave it in regular auto it bogs on hills and shifts at too low rpm making me concerned about the turbo vanes. If I drive aggressively in reg auto mode it shifts just fine, but not when light on the pedal.

 

[2004STARWARSTDI]

ULSD economy

How will ULSD fuel affect the power and fuel economy of existing diesel cars, trucks and non-road engines and equipment?A. Under typical operating conditions, there should be no noticeable impact on overall power using ULSD fuel.* Fuel economy may be reduced slightly because the process that removes sulfur also can reduce the energy content of the fuel.*
Q. Will ULSD fuel affect the performance of my vehicle?
A. Engine and vehicle manufacturers expect ULSD fuel to be fully compatible with the existing fleet, including 2006 and earlier model year vehicles. In some instances, the introduction of ULSD fuel to older vehicles may affect fuel system components or loosen deposits in fuel tanks. As part of a good maintenance program, owners and operators of existing cars, trucks and buses are encouraged to monitor their diesel-powered vehicles closely for potential fuel system leaks or premature fuel filter plugging during the change-over to ULSD fuel.