* Damage rubber fuel lines and seals: Ethanol is more corrosive than pure gasoline. Over time, this can lead to leaks and fuel system failures.
* Increase the rate of fuel system corrosion: Similar to the above point, the increased corrosiveness can accelerate rust and deterioration within the fuel tank and lines.
* Reduce fuel economy slightly: Ethanol has a lower energy density than gasoline, meaning you might see slightly reduced fuel mileage.
The extent of these issues depends on several factors including the condition of the fuel system, the climate, and how frequently the vehicle is used. Many 2000 Wranglers are still running on E10 with no major problems, but it's not advisable for long-term reliability.
In short: It will likely run, but using E85 (85% ethanol) is strongly discouraged, and sticking to pure gasoline (if available) or E0 (gasoline without ethanol) would be best for the longevity of your Jeep's fuel system.
