While taking it easy on the engine during the break-in period, we ended up with the exact same mileage numbers we had with the 4.0L. Once we uncorked the power at the end of the break-in period, that decreased. To date, we’ve run 373.94 gallons of gas through the truck since we swapped the engine. Our average mileage has been 13.6 mpg over 5,091.6 miles. Compare that to our ’01 Wrangler with a manual transmission, 4.56 gears, a Dana 44 rear, and 33-inch tires over 5,271 miles for 14.2 mpg over the same kind of terrain. Bear in mind that those numbers include wheeling in Moab and other locations, sitting in traffic, dyno runs, as well as highway mileage for both vehicles.