2008 XC70 Apparent misleading reading on fuel gage

[stefmit]

Disclaimer: no recent major work or changes on my car.

Problem: as of a few days ago the fuel gage seems to not climb above 3/4 of its scale, after filling the gas tank. A couple of items for clarification:
- by "filling the tank with gas" I imply utilization of the gas stations pump with auto shut-off. One time I attempted to override that mechanism, to determine if the gage was indeed accurate, and maybe something else kept triggering the pumps shutdown, and sure enough the gas spilled out of the tank => the gage looks like faulty
- after last round of gas tank filling, this morning, not only did the gage show 3/4 filling level, as lately, but after having driven for no more that 5miles, the gage dropped another 3/8s

Any idea what I could do, short of paying a visit to my $$$$ friendly Volvo dealer? Could I safely use the mileage to approximate the gas needs, based on the average of intra and inter cities driving I am doing?

One note: for some odd reasons (maybe indicative of a larger circuitry problem, albeit with no logical explanation on why malfunctioning of gage, vs complete shut off) approximately during the same time that the gage started malfunctioning I started blowing the fuse for the cigarette lighter. Like many others, I use that extensively to power my gadgets, and after having replaced USB cables and various power adapters, I still have a 3-4 days cadence of fuse blow ups (I am now at my 4th in the last two weeks). Correlation? Causation? Neither?

TIA,
Stefan

[kcodyjr]

Does sound like you've got an intermittent short somewhere, but it is a guess.

A subtler corrleation is that maybe you're getting fuse blow-ups when the tank is down to a certain point? If the fuel level sender is using a voltage signal, this would tend to confirm a short to the cig lighter circuit. As the level in the tank drops, so would the voltage on the sender, raising the differential between that wire and the 12V in the presumably nearby cig power wire, until enough current flows to blow the fuse.

Does anyone know where the fuel level sender and cig power circuits cross near or run together?

If you're prepared to pull away interior panels to chase wires, you could try following the fuel gauge sender forward from the tank. I'm not real familiar with the 08's, so I can't help you with the details.