I've recently noticed that my Legacy's gas gauge may be lying to me. I normally get roughly 350 to 400 miles per tank, but lately I'm barely getting to 300 miles before the gauge indicates I'm low on fuel. I almost always calculate miles/gallon when I refuel, and since I noticed the problem I'm still getting 30mpg. After I noticed that, I started keeping track of how much fuel I've been putting into it and it always seems like less than a full tank; I think it's a 14 gallon and lately its only been taking 9 or 10 gallons, so either my tank shrunk or the gauge is wrong!
Does anyone here know if this is a common problem, or how to test/fix it?