Another reason not to top off or overfill the tank is these little vents on top of the tank. What they look like exactly will differ depending on the year and model of your Jeep, and many newer Jeeps have them formed directly into the top of the tank. Whether it is formed into the top of the tank or fit with a seal as seen here, the point is the same. They are designed for vapor, not liquid, and feeding liquid through them can kill both the vent and the rubber surrounding it. They should function like a one-way valve letting air out, but not in.