Fuel calculation broken after 30K service

[ultranaut]

Last night I put 14.492 gallons of diesel into my 2010 Golf TDI. I've had my car for a year now and know what to expect from it, but this is the second time I've nearly run out of fuel since I brought it in for it's 30K service one month ago. Until recently the "miles remaining" behaved in a relatively predictable manner. I've never relied on it to be precise, but I've found it accurate enough to rely on when deciding if I should fuel up at the beginning or the end of my 75 mile commute.

Twice now it has said I have 100 miles remaining only to hit 0 remaining after between 60 and 70 miles of driving. The obvious cause would be a decline in fuel efficiency, except there isn't one. In fact, last night I drove to maximize fuel efficiency for the 65 miles between starting the car and refueling, I was at 49 mpg average (per the cars calculation) . Normally on my commute I'm hitting around 41 mpg average, so if anything the 100 miles remaining estimate should of been conservative relative to typical fuel consumption rates.

After refueling the miles remaining went up to 550. This is within the normal range for a full tank.

Does anyone have any idea what may be causing this problem?

 

[ihatespeed]

my miles to empty is pretty flaky too, especially under 30 miles to empty, not bad compared to my old altima though, that had a very sketchy fuel consumption meter.. My JSW says refuel with about 40-50 miles remaining and if I do right then it takes ~13 gal.. I ran it 10 miles past 0 once, left home w/o my wallet and it took 14 flat, I was super paranoid and trying nearly every hyper milling technique I could think of to make it to the station. . I have begun reseting my trip meter and my trip 2 consumption meter at each fill up, I watch the trip meter, and the fuel gauge and make a gut decision based loosely in math and fuzzy logic. I also put a 20 in the glove box should I need to fuel sans wallet ever again. I basically just fuel at about 550 miles whether it needs it or not.

As for cause of the change in behavior:
Part of your 30k service may have included a software "upgrade" changing some minor calculation somewhere..
otherwise I might suspect low ambient temperature throwing off your fuel gauge. Have you been doing real mileage calculations? (fill and divide into trip meter?) If it was me I'd use the trip meter, if over 500 I'd fuel before if under I'd fuel at destination. should keep you out of the weeds.. assuming you get at least 40 mpg 575 miles should leave you with at least a 1/2 gal in the tank.

 

[MayorDJQ]

Seriously? When the light comes on you have ~1.9 gallons remaining. Plan accordingly.

I doubt there's anything wrong with your MFD or fuel gauge. The miles-to-empty calculation can change quickly. It's based on the average MPG-1 times fuel remaining. Once the fuel level gets low, the predicted distance can drop rapidly if the MPG-1 goes down.

 

[silversx80]

I reset the #2 trip odo, and the MFD lower-right odo every full tank. When those hit 500 miles, I fill up at the next available station (or the next time I pass my typical station on my commute).

 

[ToeBall]

Maybe it's because I used to live in the large desert that is west Texas and learned to drive out there, but as a general rule of thumb, I don't try to stretch my tanks by that much. I'm quite ok with tanking up at 1/4 tank remaining. That leaves me a 100-200 mile reserve if needed for an emergency. Already been through one evacuation and two floods since I moved to Houston so it's not just paranoia on my part. The other thing to remember is that the emptier your tank gets, the more air is in it; the more air, the more moisture, and condensation, and water in fuel.

 

[DWalk]

and the MFD lower-right odo

I am an idiot and can't figure out how to reset. How did you do it?

 

[RebelTDI]

I am an idiot and can't figure out how to reset. How did you do it?

In the lower right corner below the speedometer is a rectangular button. Push it on hold for a couple seconds and the trip odo will go to 0.

I agree with Toeball about keeping the tank topped off more than letting it go to empty. More opportunity for condensation and moisture in the fuel. Others have mentioned a metal rod in the tank as a source of rust that can accumulate at the fuel filter. I know people like to try to see how many miles they can squeeze out of a tank in a TDI, but there may be some unwanted side effects of letting your tank run low for prolonged periods.

 

[chilehead19]

It does seem foolproof to me. If you pay attention the low fuel light will warn you. start looking for fuel in the next 50 miles or less and you will be safe