Gas being lost

Hi All
I have a 2000 4wd. 260+ miles.. I only drive about 2000 miles a year now. The fuel level keeps dropping without driving it. It does sit outside and its in the 80's+ (over 100 recently) I figure I'm getting maybe 9 MPG based on refueling.. No leaks that I can find. No smells.. Evaporation maybe? Gas cap is original, no error codes. Any thoughts?

 

fuel loses its combustibility/octane over time.

basically the engine needs to use to more to get the same results. Which may explain your poor MPG.

can't chime in on the fuel loss though. That's a new one

 

I based the 9 MPG on the fuel disappering from the tank. Driving I still get about 18 MPG, after 20 years a don't check it anymore. If I left it parked I think the tank would go dry...

 

Where do you live? The 2000 should have a locking fuel door, but obviously before wracking our brains for every possible source of fuel loss, ruling out theft seems important.

And ruling out kids sneaking the keys and running errands.

 

Probably worth it to change the gas cap too.