bad mileage again.. any one else?

Andrewh

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Aug 1, 2006
Location
Allen, TX
2006 jetta
was getting around 36 37 in town.
About a year or so ago it did this and I changed the fuel filter. Not sure if it did anything, but it eventually came back up in mileage from 30mpg back up to the 36mpg.
I have another 7k miles on it since then, and the last calc I did showed I had dropped again to 30mpg.
Anyone else have this problem. Only 17k miles on the car right now.
Could it be the filter again?
 

Joe_Meehan

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Sep 3, 2005
Location
Ohio USA
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NB TDI, 2002.5, Silver
I am going to guess it has nothing to do with the filter, either time. It would be rare that a fuel filter in 17,000 miles (or really any miles) would reduce mileage like that.

Could you tell us exactly how you are measuring the mileage? City or highway? Summer or winter?
 

Andrewh

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Aug 1, 2006
Location
Allen, TX
I just do the usual. I reset the trip odometer everytime I fill up. When I fill up again, I try to fill it till I see diesel, not just foam at the top of the filler tube.
Then calculate how much I got in mileage.
I do a bit of mixed driving, but mostly city, stop and go type stuff I only fill up every 2 to 3 weeks, so it is pretty easy to track.
I have been adding diesel kleen and 2 stroke oil for about a year now. So I don' t think that has done anything.
Summer and winter driving. Bought it new in june of 06. Watched the mileage start at 30 and then work its way up to 36. Never gotten any better than that.
Last year or so it dropped to 30, so I changed the filter. It eventually went back up to 36 and has been that way for the last 7k miles.
Temp has been up a bit, but I ran a/c all last year too.
Fill up at the same place each time. Pretty busy Krogers. Always see pickups filling at the diesel pump, and it always looks clear when I see it coming up the filler neck.
 

8606

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Dearborn MI
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06 Jetta-sold
My last fill up I got 42.05 mpg. I expected 43-44mpg. The heat and using the ac at max setting has not helped. I would guess its at least as hot (probably hotter) where you are at. I don't get stuck in a lot of stop and go traffic, if I did I would not think 37 or even 30mpg would be out of line.
 

SBAtdijetta

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Houston, TX
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'10 Jetta Cup 6spd, '02 Jetta Auto
Kind of OT but I would not be putting 2 stroke oil in your PD, Diesel kleen will be just fine to add lubricity and Cetane.

What is your tire pressure at? My MPG can drop hard in the city if I drive aggressively and don’t have my tires aired up close to 40psi.
 

Joe_Meehan

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NB TDI, 2002.5, Silver
Andrewh said:
I just do the usual. I reset the trip odometer everytime I fill up. When I fill up again, I try ...
That sounds fine, you should be getting accurate numbers.
 

Andrewh

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Aug 1, 2006
Location
Allen, TX
Hmm, hadn't thought about that. Just got new tires on the car. Have to check that.

2 stroke ashless is listed as one of the additives people use on PD motors, so I don't think it is a problem.
 

SootHappens

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Scappoose, OR
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2006 Jetta TDI
another vote for 'no 2-stroke oil' here... I had some Marvel Mystery Oil laying around and dumped it in... Terrible mileage that tank and for several afterwards... I even threw a couple 'overboost' codes when that stuff was in there, and Marvel is thinner than 2-stroke. !!
 

SuperJ

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Waterloo, ON
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2006 Jetta TDI
the jets in a 2 stroke carb or fuel injectors are magnitudes larger than the tiny holes in our high pressure diesel injectors. You're asking for trouble putting 2-stroke oil in your fuel. Stay to proven diesel additives.
 

2004STARWARSTDI

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2004 Platinum Gray GLS Jetta / 2006 Silver Jetta with DSG
2 stroke oil

Another vote for NO on 2 stroke oil. PD TDI are different from preevious TDIs and you are asking for trouble. Check the price of a PD injector $$$ compared to a regular TDI injector $$. :eek: Then you will think twice about your 2 stroke oil decision!:mad:
 

Mach1

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The injectors are only $600 new from the dealer, I use the ashless 2 stroke oil in my PD. I would rather use the 2 stroke oil then the Biodiesel.
 

06SpiceRedTDI

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ehhh, uhhhh 2-stroke oil???:confused: I don't usually put anything extra in mine, I tried Redline, PS Silver, BG, and Standyne, nothing seemed to make any noticable increases in mileage. I did run 1 tank of B99 a couple of tanks back just for its cleaning properties. My last tank was my best tank yet 739.3 miles I averaged 51.27 MPG with absolutely NO additives. All the additives do is increase the cost per mile. $66.31/739.3=$0.089 per mile if I add a 4 dollar bottle of injector cleaner we get $70.31/739.3=$0.095 per mile. Now if you take the increased cost and divide by the original cost per mile without additives ($70.31/$0.089=790) you need to get 790 miles on that same tank to break even, that is 3.51 MPG more average which I haven't seen with any additive yet 790/14.419=54.78
 

SBAtdijetta

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True I would agree you may not see a cent per mile gain with some or all additives, even good ones. But, you are also better maintaining the fuel system IMHO, so I use Stanadyne, and sometimes run a small Bio %. But only when I happen to be near the Bio retailer already. (I top off and fill a 5 gallon diesel container for mixing a bit per tank later)

Mach,
Are the PD injectors $600/unit, not total right? 2 stroke is your call of course as its your car and I know you know way more than I do, but I would rather do Power Service, Stanadyne, or B2 - B5.

Steve
 

Andrewh

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Aug 1, 2006
Location
Allen, TX
Hmm, I was adding it because there is a post about adding lubrcity(sp) to the low sulfer diesel.
Showed that it helped. Ah well. Regardless, I am a little concerned about my lack of mileage compared to everyone else.
Haven't had a chance to check tire pressure yet. Just switched from the oem contentals to good year triple tread.
Not sure if that affects mileage at all. Can't imagine a 20 percent decrease by changing tires. Same size and everything.
 

Harvieux

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There was a post awhile back where some R&D company tested many popular diesel fuel additives and 2-stroke oil was included. The best overall performing substance for lubricity was a 2% or B2 bio-diesel mix. Later!
 

06SpiceRedTDI

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Andrewh said:
Hmm, I was adding it because there is a post about adding lubrcity(sp) to the low sulfer diesel.
Showed that it helped. Ah well. Regardless, I am a little concerned about my lack of mileage compared to everyone else.
Haven't had a chance to check tire pressure yet. Just switched from the oem contentals to good year triple tread.
Not sure if that affects mileage at all. Can't imagine a 20 percent decrease by changing tires. Same size and everything.
While I would see the need for the extra lubricity in an ALH with an injection pump that is lubricated by the fuel, I am pretty sure that the PD is designed to run on ULSD and is just fine with the stock set of lubricants that have been added to ULSD by oil companies so that it can be run in older diesels without ill effects. If you are that worried about the Lubricity B5 Biodiesel has more than the old Low sulfer D2, Has really good cleaning properties, and will not void your warranty (not that PS or any other additive will either).
 
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1998993C2S

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2006.5 Jetta Pkg2 DSG Navi
As far as MPG goes.... our MPG results are not unlike the OT. City driving yields about 36 MPG consistently measured the old fashion way; tires at 42+psi, light accelerator pedal, drive the torque curve practices, sometimes A/C sometimes not. For whatever reason and what seems out of the blue, the MPG will drop to 33/32 MPG/city in our TDI as well. Go figure. Still respectable City MPG for such a substantial car is my take.
As an aside: We recently completed a ATL- DEN (1500mi) road trip and the MPG's were in the high 30’s / low 40's range all the while traveling at speeds over 75MPH - sometimes 85. Colorado has a 75mph limit on its interstate hwy's, so pushing the issue to 85+mph is often the traffic’s practice. 41/42 at 75+ on average is respectable. When traveling slower at 65mph or less, man does this speed impact the MPG performance.

OT: I'd look to the variance in speed as the culprit for your diminishing MPG performance. Hey "Speed Kills" (says the guy who will do 85+)
 
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SBAtdijetta

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'10 Jetta Cup 6spd, '02 Jetta Auto
Yea but the OP is mostly city so 85+ speeds are not his issue lol I hope not anyway.. So I still think it is a combo, new tires, tire PSI, and maybe one of the following (a bit harder driving/crappy fuel/fuel filter).

Tire PSI would be first on my list to check.
 

1998993C2S

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Does the "cetane" value in our fuel source (in my case it’s a Shell station and whoever their refiner is) vary a great deal? And, by adding xzy ounces of Power Service, etc. fuel conditioner(s) does this impact the cetane value so much? Is the cetane value all over the map? Is this the accepted expectation?

Having owned a 95' E300 diesel (new) the MB dealership service once indicated that the engine difficulty I was having was attributed to a low cetane tank of diesel fuel. When asked how he/this was determined, the "low cetane" conversation ended. When asked again for the service writer to back this up (politely speaking) he could not. Nuff said. Anyway, the engine issue was the E300's dual stage resonance intake.

Back to the cetane values - is there a road side test in simple terms? I would think diminished cetane values would greatly affect the city MPG performance.
 
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Mach1

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05.5 Jetta 5 spd, 06 Jetta DE DSG, 04 F250 6L, 2000 F250 7.3L
Yes, the Cetane varies greatly, We barely can find 40 cetane her in Texas, We use a heavy dose of cetane improvers..

The PD's were designed to run on 50 cetane(good luck finding anything close to that)euro spec fuel.

When you do a combination of cetane boosters or quality fuel, your TDI is going to love you, They run entirely different with the correct fuel. Very strong and smooth, and no more rattling..
 

Mach1

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Yes, thats a brand new unit injector from the dealer for the low cost of $600 ea.

The refineries use N2 to scrub the sulfer out of the diesel, several passes are needed. During the process, some of the lubricity is removed/lost.

In the unit injector, any extra lube is welcome, but then I am going to keep mine for 300000.

I use all the good additives, including PS and Diesel treat 2000. I used to usse bio and a small percent is good, I dont like what bio does to a fuel system though, and it doesn't get along with Variable vane turbo's from waht I have seen.
 

Andrewh

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Aug 1, 2006
Location
Allen, TX
I do get to 85 sometimes, but my daily commute sees nothing over 45mph.
I will check air pressure this weekend, but I generally don't run more than 35psi in my tires anyway.

I guess it might be normal to get 36mpg, I just didn't see that in anyones mileage postings. I just learned to live with it.
But dropping to 30 again, seemed a bit much.
 

Mach1

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You are losing some FE by only having 35psi in the tires, some on here run 48psi, thats a bit for me, however I run 42psi in mine..But I drive a good portion of highway.
 

F250_JR

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I can't give any city numbers for my 2005.5 Jetta, because I have not had it long enough, but my dad got 40 mpg @ 80 mph (w/ a couple of 100-120 mph bursts) on a recent road trip, and on the way back, I got 42.5 @ 75 mph with diesel kleen added. I'm pretty satisfied with those numbers for those types of high speeds. That said, with the type of stop and go driving that I do in city, I am sort of expecting somewhere between 28-36 mpg for tanks with only in city driving.

Back to the question, could changes in driving conditions like long stretches of construction achieve sudden drops in fuel economy like AndrewH is experiencing? Say he does "rural" in city driving on a regular basis, then his daily commute route gets a long stretch of construction with 3x the stops. Or, maybe another family member with more aggressive driving habits drove for half or more of this last tank. Add a situation like one of those on top of the new tires that might have a higher rolling resistance, and also might be underinflated, and I could realistically see a 6-7 mpg drop.

Don't know if this helps or not, just my first thoughts on the topic.
 

8606

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Dearborn MI
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Filled up today-41.26 mpg (and that's with Power Service grey). I just ordered a scan gauge, hopefully this will help me to make adjustments to my driving and increase mpg.
 

MalcolmBurke

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Garrison
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SBAtdijetta said:
True I would agree you may not see a cent per mile gain with some or all additives, even good ones. But, you are also better maintaining the fuel system IMHO, so I use Stanadyne, and sometimes run a small Bio %. But only when I happen to be near the Bio retailer already. (I top off and fill a 5 gallon diesel container for mixing a bit per tank later)

Mach,
Are the PD injectors $600/unit, not total right? 2 stroke is your call of course as its your car and I know you know way more than I do, but I would rather do Power Service, Stanadyne, or B2 - B5.

Steve
Gee I get to 400 and the tank light goes on. maybe I have a special model? I do use AC full time as I live in the hot zone. Without AC the light goes on at 450 miles
 

Mach1

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05.5 Jetta 5 spd, 06 Jetta DE DSG, 04 F250 6L, 2000 F250 7.3L
MB, Do you fill yours up all the way? I get to 1/2 tank and have 440 miles on mine. I get right at 700 MPT. Local/AC use its 100 here in Texas.
 

Andrewh

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Aug 1, 2006
Location
Allen, TX
Well, filled up again this week, and it went up to 32 mpg. Don't know.
Checked the tires and they were at 32 psi. Aired them up to 42. Says max of 44 on the tires.
Guess I will see next fill up. At 160 miles on this tank and already past the 3/4 mark on the gauge.
 
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