Been waiting for someone to bring up this one. Mothballs has long been a diy additive for mileage. Found this website searching additives and thought I'd post it here:
My person experience goes back 25 years when I was but a youngster. One of first mileage tricks I tried. Used off and on for years. Have found it usually improves mileage and economy. However I also believe it caused the filter to plug and took out the pump on one vehicle I tried it on.
Anyone else played with this?