I am new to this so I don't know if this is how I post a question.
I have an '89 Lariat that I bought from a private sale. I have since discovered that the rear tank doesn't hold gas. I fill it up and within 3 or 4 days it's mostly gone. Initially I thought someone was siphoning gas so I got locking gas caps; but it still happens. So I have been using the front tank and had been getting about 19 mpg. But lately I've been getting less than 9 mpg. That's about 150 mile on a tank of gas. What's going on?