Strange fuel mileage lately after phase 2

epssax

Veteran Member
Joined
Mar 26, 2001
Location
Louisville, KY
TDI
2014 JSW, SEL, 74K
I bought a new 2015 Jetta last August.. Had only phase 1 and got 41-42 in suburban driving with gobs of torque. Got my phase 2 done with mileage drop to 38 under same conditions. I was disappointed and wrote VWofA. They sent me back for a re-tune and the dealer said there are no codes so we can't do anything more.


I went 100 miles out of town and needed a fill so bought local diesel there. I noticed I was getting better mpg according to my dash read out. Not believing it much I was surprised by the next fuel purchase, 41 mpg. The next was 42. I have gotten 44 the last two fill ups. I fill up between 300-400 miles. Went on the road this weekend and the readout on the dash reads 53.1!


I started adding a little Lucas fuel conditioner about that time.

The torque and shift points on my DSG haven't changed but my mileage sure has. I'll keep following this PLEASANT change in mpg! I am sure something has caused my tdi to use less fuel.


I am using fuelly to compute my mpg, BTW.
 

Mythdoc

Veteran Member
Joined
Jan 28, 2017
Location
Tennessee
TDI
2011 Touareg, 2015 Q5, 2015 Golf
I bought a new 2015 Jetta last August.. Had only phase 1 and got 41-42 in suburban driving with gobs of torque. Got my phase 2 done with mileage drop to 38 under same conditions. I was disappointed and wrote VWofA. They sent me back for a re-tune and the dealer said there are no codes so we can't do anything more.


I went 100 miles out of town and needed a fill so bought local diesel there. I noticed I was getting better mpg according to my dash read out. Not believing it much I was surprised by the next fuel purchase, 41 mpg. The next was 42. I have gotten 44 the last two fill ups. I fill up between 300-400 miles. Went on the road this weekend and the readout on the dash reads 53.1!


I started adding a little Lucas fuel conditioner about that time.

The torque and shift points on my DSG haven't changed but my mileage sure has. I'll keep following this PLEASANT change in mpg! I am sure something has caused my tdi to use less fuel.


I am using fuelly to compute my mpg, BTW.

It is well known that diesel varies a lot from pump to pump and from chain to chain. The Flash Foods chain in S. Georgia always falls 10-15% below my overall avg. for instance.
 

Graham Line

Veteran Member
Joined
Apr 18, 2012
Location
Pacific Northwest
TDI
'12 Golf TDI 6M
There's also some internal learning going on. My '12 felt like a slug the first 50-100 miles after "the fix." After some, uh, brisk driving it's performing quite well.
 

epssax

Veteran Member
Joined
Mar 26, 2001
Location
Louisville, KY
TDI
2014 JSW, SEL, 74K
More

There's also some internal learning going on. My '12 felt like a slug the first 50-100 miles after "the fix." After some, uh, brisk driving it's performing quite well.
My phase 2’was in June. Even did some 100 mile trips since. The surprise here is that all of a sudden some good fuel numbers.
We will see.......
 

CTD_Chevrolet

Veteran Member
Joined
May 31, 2011
Location
Montucky
TDI
'15 Jetta S DSG, '02 Jetta ALH 5spd
Fuel quality can definitely make a difference. Start logging it on every fill (I use fuelly) and note where you got the fuel. You'll find trends and before you know it you'll lose your **** when the pumps are out of order at your preferred station :D
 

Borsig

Vendor , w/Business number
Joined
Oct 22, 2009
Location
va
TDI
2015 Golf TDI SE, 2015 GSW SEL (buyback), 2011 JSW (sold)
Use fuelly.

I've recorded every fillup on my last two TDIs. I only have pahse 1 on the golf. the wagon was bought back.
 

dodgeit

Member
Joined
Dec 4, 2016
Location
South Carolina
TDI
Jetta
My Hand calculated mileage went up after the first fill up (48), after having phase 2 done. It has went back down to Phase 1 fix levels (44-45), and has stayed there since phase 2 being done in July. No codes, performance is good. Dealer told me that intakes were clogging with egr soot on some of the phase 1 cars. Checked tire pressure they are on the money. will start looking at better places to fuel up. Pre change I was always hand calculated (48 and change). Still filling up at the same place.
 

740GLE

Top Post Dawg
Joined
Aug 19, 2009
Location
NH
TDI
2015 Passat SEL, 2017 Alltrack SE; BB 2010 Sedan Man; 2012 Passat,
To the OP, I'll mark it up to the driving conditions, if you had a routine commute of 100 miles a day, 5 days a week it'd be pretty easy to point to the tune and "the fix". Remember mix a regen or two over a tank, it'll take a good bite out of economy.

One thing I noticed in our '15 (phase 1, so take that for what it's worth) is that a regen takes a looonnng time to finish, noticed one last week on a 150 mile trip for work, lasted about 15-20 min on the highway at 70mph, EGT prob 3 stayed pegged around 1100-1300F, that's a long time of eating extra fuel. So if you're driving around town say 5-10 mile trips, you're prob not finishing regens until you get out on the highway.

But comparing driving 300 miles around town in a couple weeks vs a a long straight shot highway run of 300 miles are two different driving environments.
 
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