Fuel Tank -16 gallons.....why can I only put in 10 gallons?

So did you find out where "E" really is? You could also try siphoning out the gas when your guage reads "E" (or really close to it) and see how much you get out.

Two good ideas. Run tank out or siphon fuel out when on empty. Either one should help get to the bottom of the problem.
My fuel gage. E is full F is empty?