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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 February 12th, 2019, 17:13   #1
Join Date: Dec 2018
Location: Puerto Rico
TDI(s): Passat 2012
Default Low mile per gallon TDI Passat 201

My 2012 TDI Passat reports an estimate of 39 miles per gallon but when calculating the miles per gallons after a refill it comes out to ~25 miles/gallon.
I did a EGR valve cleaning, EGR differential pressure sensor and upstream oxygen sensor replacement. That took care of the engine light. But the mile/gallon still remain low. In addition, the diesel particle filter is reported as been done more frequently than expected. Which I think is related to the high diesel consumption and poor combustion. I haven't change the downstream oxygen sensor, but not flagged as defective.
What else can I check?
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Old February 13th, 2019, 10:06   #2
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ToBiN's Avatar
Join Date: Feb 2017
Location: Colorado
Fuel Economy: 36 - 37 mpg Malone Stage2

That's a tough one. I read on CruzeTalk that those diesel owners are cleaning their oxy and pressure sensors and gaining a couple mpg. Looks like you are missing about 10 - 15 mpg.

Does the car "feel" normal? Is the turbo spooling? Also, does it pull to the left or right while driving? are you tires wearing correctly? Possible alignment issue? Also, feel your exhaust. Is it free flowing or can block off your exhaust pipe with your hand or will the exhaust blow your hand away? If you remove your oil cap while its running, how much blowby is there? Can you flip your oil cap over and it will still "sit" over the hole or does the pressure coming out of the crankcase blow the cap off? How many miles are on your TDI?

Clean paper air filter. Quality diesel fuel. OEM recommended oil. Proper interval changes. fuel filter. All things to be considered. Also speed, I made 40-42mpg on my TDI running 80mph but heard of others making 50s. The 50mpg guys said to slow down and then I would realize better mpgs. I did, I made 50s on a trip, but it was on some back roads with lower speeds. Don't have a heavy foot. Stay away from stop and go traffic and idling.
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Old February 14th, 2019, 06:30   #3
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Join Date: Mar 2005
Location: Old Hickory, TN. Settling here...

DPF regeneration frequency fault indicates ECM knows there is too much soot and needs to regen, but it's happening too much. I find that air leaks are biggest cause.

We have found pinched or damaged o-rings in charge air hose connections, cracked charge air pipes, split charge air hoses, and damaged charge air coolers are biggest causes.

I would guess the short trips and slower speeds in PR would not help either. Cleaning the EGR valve and replacing the sensors is probably fixing a combination of driving habit and some damage somewhere.

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Old February 21st, 2019, 17:33   #4
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Join Date: Feb 2012
Location: Cowford, FL

So my buddy had this same problem on a 201X Jetta (Don't know the year but it was a Mk6 Jetta). He got the fix done and was getting <30 mpg after the fix. He left the battery disconnected overnight and he was back to 42-48 mpg.

I don't know the how or why, but it happened.
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Old February 25th, 2019, 18:37   #5
Join Date: Dec 2018
Location: Puerto Rico
TDI(s): Passat 2012

Thanks for the tip. I will try it.
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