My '97 TJ, 4.0, 5 speed, 290,000miles, uncorrected speedometer has averaged 14.24 mpg over the last 6 tanks. Low of 12.55, high of 16.91.....I found it is happiest at about 1250 to 1500 rpms in 5th gear. that works out to 55 to 60 mph. I believe my speedometer is off by about 10% over the whole range...Most of my driving is just putting around. Highest mileage was the week I drove 30 miles round trip every day on state roads 55-60 mph. Lowest was the week I went 4 wheeling once or twice .....
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