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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 August 1st, 2019, 21:20   #1
Join Date: Jul 2019
Location: TX
TDI(s): '11 JSW
Default JSW TDI horrible mpg

Long-time lurker, first-time poster here.

A short backstory, I picked up 2011 buyback JSW TDI DSG about 3 months ago. It only had 57K miles on it, in great shape with lots of maintenance done by the dealer pre-sale, including new timing belt. I bought it in OH and drove it back to TX averaging 42 mpg on the highway. Once I got it home, I started tracking the MPG via fuelly app. This is where things got interesting. My commute is identical, traffic is pretty much the same, my driving habits haven't changed and I get my diesel at the same exact station, down to the same exact pump every week. I went from 37.5MPG my very first fillup, down to 25.2 mpg on today's fillup. What the hell could be causing my MPG to progressively go down with each fillup? It came down 12.3 mpg spread over 9 fillups, dropping about 1.3 mpg avg with every fill?

I ruled air filter (looks brand new), replaced fuel filter 2 fillups ago, switched from Stanadyne to Schaeffer's fuel additive, to no avail.. mpg continues to steadily drop. I'm all out of ideas other than something is going on with the EGT/DPF and whatever else they replaced during the buyback deal that's getting clogged up at a crazy rate.

Some other factors to consider/rule out - temps in Houston have been about the same on my commute back from work, but in the mornings its been significantly cooler in the last 2 weeks (or 2 fill-ups), so much so that I've driven a few mornings without AC on which should have theoretically returned better mpg.

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Old August 7th, 2019, 07:55   #2
Théoricien -TDIClub Contributor
dieseleux's Avatar
Join Date: Nov 2006
Location: Pas assez loin pour vider ma tank!
TDI(s): Jetta TDI 02
Fuel Economy: 4.2L/100km

Brake drag, check rear break temperature at highway exit.
If all good, center wheel hub are same temp on 4 corner.
Check tire pressure also...

Si votre seul outil est un marteau, toute les solution ressemble à des clou.
If your only tool is a hammer, all the solution looks like nail.

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Old August 7th, 2019, 09:50   #3
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Join Date: Dec 2001
Location: St Louis
Fuel Economy: fantastic

Sigh... :

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