Vw passat fuel gage issues

I have a 07 passat and the fuel gage has just started acting a little odd, last week when I turned the car on it read that it was empty (it was at least quarter full) and rectified itself the next time I used it, this afternoon it reads as 3/4 full when It was only half tank this morning.
Any idea on the issue and if it's costly to repair?
thanks

Typical euro. They're so economical it adds gas to your tank when you aren't watching. Gotta love that.

Weird, if it was a loose connection then it would normally read either correct or low/high. I suspect more than just a loose connection. Are you sure it has only half a tank, not 3/4?

Perhaps try filling it up, and record the KM so you can make an estimate on your fuel quantity.

A likely possibility could be the fuel gauge sender unit, which is part of the in tank fuel pump assembly on one of those I would expect. Shouldn't be too hard to remove and test it, if I had to take a guess I would say an hour or two's labour.

Cost for the part if that is what proves faulty, could be a few hundred dollars if the whole pump/sender unit is replaced.

Best to call a third party VW specialist for some ideas on pricing though. Otherwise a good auto sparky might be a good one for diagnosis/testing.

I would tend to keep the tank well full and monitor it a little more before taking it for diagnosis. Just to see if it's an intermittent problem (harder to diagnose) and also to give better feedback as to what the problem is to the technician. Just take care you don't run it low or out of gas, that is a very bad thing with a late model car, especially one of those Passat's so err on the side of caution.

You haven't by chance been running an ethanol fuel blend have you? (Gull or Mobil 98).

98 gull was put in over the weekend (normally It's 95)

Interesting, which motor is it running?

It may well just be complete co-incidence but I am wondering whether the solvent effect of the ethanol has upset it (maybe washed some muck from around the tank, damaged a non compatible part etc) or whether it's picked up some water from the tank given it's hygroscopic.

I think we should start with checking whether your car is actually E10 compatible (some VW's of the era are not) but I have to rush off now.

Post the details of which engine you have and I will respond this evening. I am also wondering whether there is any value in having the tank drained and refilled with BP Ultimate 98 (what it should be running). It's a bit of a hassle/cost to go to on what is a bit of a long shot and the damage may already be done if I am right anyways.

Also, if it was my car I would be changing the fuel filter, it should be done every couple of years or so anyway. Perhaps leave it until after another full tank of 98.

I would suggest you don't run any sort of ethanol blend in your car, and most definitely don't if it's one of the models VW say not to run it in.

Disclaimer, the above is my opinion only.

C&P. From a VW Passatworld Forum.

Passat W8 Fuel Gauge problems

Hi all,

Since a few weeks its starting to get cold here in WI. My fuel gauge is starting to act strange, sometimes in the cold it wont show anything while the tank is full. The gauge keeps showing that the tank is empty but the MFD doesn't show anything and there is no please refuel sign. When i turn the key on and off repeatedly, the gauge comes up but than falls back to empty. When it it is warmer or the car stood all night in the garage i don't have any problems and the gauge works well. Last winter i didn't have any problems with the gauge while the car was standing outside. Is there anyone who is familiar with this problem or knows what could cause the problem?
Regards, Jordy
Answer's.
Sounds like you have very common problem for VW on your fuel sending unit where there is too much deposit on the variable resistor which causes bad connections. Try some good fuel injector cleaner such as Chevron Techron for several tanks of refill and see if it resolves your problem. There are recalls on certain models on sending unit but you have to check with your dealer and see if yours is covered. Or you may have to replace the sending unit and make sure to use tier 1 gasoline from now on.

IIRC, the gauge sending unit on W8's can cause other electrical things to act up when they go bad.

For the remainder of the forum answers here's the link.
http://www.passatworld.com/forums/b5-garage/321415-passat-w8-fuel-gauge-problems.html

While this is a completely different and newer series of Passat that the OP has, I am thinking along similar lines. The erratic behaviour of the needle as opposed to just dieing or either working or not suggests an unintended change in resistance. Some filth being washed in to the variable resistor or possibly some corrosion of the resistor are what's on my mind.
That's why I am thinking give it a fresh full tank of BP Ultimate 98 before rushing to have it repaired. The disturbance of muck is why I recommend a filter change, extra important being a direct injected vehicle.

Just had a little look for you, your car is just new enough that it should be E10 compatible, but especially if it's a Japanese import I can't be 100% sure.

Even as a supposedly compatible vehicle though, that wouldn't help at all with my suspected scenario of the E10 disturbing some muck in the tank or possibly causing some corrosion (it would be awful quick for corrosion though in fairness).

So, my advice as always which is purely based on my OPINION is to not ever run E10 blended fuel. Stick strictly to BP Ultimate 98 for your car, use a bit of 95 to get you home in a pinch, never ever use 91.

The reason for running 98 as opposed to 95 in your particular vehicle is to avoid carbon build up in the intake and on the intake valves. This is expensive to fix, your engine is also designed to give superior economy on the extra high octane fuel. So you will get any difference in price back, and some.

Best of luck with it.

Hehhehehe. I actually loathe the Euro/East Asian/U.S.A debate, because there is shiteboxes in all categories.

But that is actually quite funny LOL.