strange situation with fuel gauge (insurance, idle, engine, gas)

[kms4]

Before I take my care in after this holiday weekend, I thought I'd see if you'd be willing to share your opinions about what might be going on. This morning, I walked to my car and noticed that the gas tank cover was open. Very strange, as I had not left it this way. When I got in my car and turned on the engine, the fuel gauge read full to the very top. Again, very strange as I filled up the tank 2 days ago and drove it quite a bit. It should not be full! I drove it around a bit and the gauge did not move. There has been vandalism in my parking lot recently, so I am wondering what the heck could be going on here. Is there any way it could be possible to tamper with the sending unit or fuel gauge with no obvious entry into the car except through the gas cap!? Any thoughts? Thanks!

[Omaha Rocks]

This may sound stupid, but is it possible that somebody dumped something in your gas tank - like several gallons of water?

[Steve Bagu]

Process of elimination.

Water in the tank will mix with the gas a little and cause the engine to sputter and miss and run very rough if it runs at all.

Not sure if you have a carb or late model Fuel Injection.

A knowledged person or mechanic would be able to disconnect a fuel line to see what kind of fluid comes out from the tank before entering the engine...water will show in gasoline...they separate when allowed to sit.

You can start the car and allow it to idle for 10-15 mins and see how it runs before attempting to drive down the road and stall in the street somewhere...then needing a tow.

As a former shop owner had a similiar problem with a customer who had "sugar" put into her gas tank which I had to remove and flush...replaced the fuel pump...cleaned inside of her Carb and suggested a locking Gas Cap. She lived in a Apt complex where parking was in the open.

If it sputters...shut off quickly as there is water or some other fluid in the tank and the system will have to be cleaned...drained...blown out with air.

As a former mechanic...that is what I would do considering your situation.

Steve

[caution]

a general tip when finding the filler door open is to look for a residue / particles of any kind left behind around the end of the fuel filler tube and on the ground beside the car

even with a funnel it's hard to dump sugar, salt, dirt, oil, or other nefarious particles in the tank

if you spot something, call the cops and your insurance company without bothering to start the car

based on what you posted though, i have no clue (i'm guessing you don't take ambien or drink or both, lol)