OK first off, I am not claiming that additives, both fuel and oil, are mechanics in a bottle or fix-alls.
I have been having a problem with my fuel gauge being not accurate at all, as in I'd be at 200 miles and my fuel light would be on. Another thing, when i got the car, the gauge would be at the 3/4 mark at 75 miles and a year later it'd be at half full at 75 miles. I get 20-22 mpgs so its not that I'm getting poor mpgs. Anyways, I added two bottles of Chevron Concentrate to my fuel tank and I think it fixed my gauge. showing back to about 80-85 miles at 3/4 a tank. Went through one tank of gas and on my second. Hopefully it fixed it.