[FJtest]

"Miles per tank' is a useless unit of measure, you need to calculate actual miles per gallon, based on exact distance driven and gallons of fuel required to completely refill the tank.

I've also got a 2014, and have meticulously tracked fuel consumption since new, including through a careful a 5K mile break-in.

Dead stock, no roof rack or any other modifications, driver only, and after break-in, I was occasionally able to get 23 MPG on the freeway (flat) at a fixed 65 MPH with conservative driving.

Now I've got a hard-shell roof-top tent, full aluminum armor, sliders, fridge, on-board air compressor, aluminum front bumper, etc. and can consistently get 19-20 MPG on the freeway, again with very conservative driving. Around town, even with conservative driving (2K RPM shiftpoint, lots of closed-throttle coasting while approaching stop signs and stop lights, etc.) fuel consumption degrades to 16-18 MPG. 'Slightly' aggressive driving can easily drive that down to 14 MPG.

Any kind of headwind triggers a big increase in fuel consumption. Traveling cross-country or through mountainous areas, when approaching any kind of grade I disengage cruise control to avoid a high-RPM one or two gear downshift.

If you monitor instantaneous fuel consumption with Torque Pro or some other app, or install hardware like a Scan Gage, you will be able to see, real time, how every different combination of throttle, RPM, transmission gear, engine load, etc. affect fuel consumption. You'll be shocked to see how little throttle opening, or how little an increase in RPM, is required to drive MPG down into the single-digits.

 

[FJtest]

Are you correcting for the huge (>15%) speedometer and odometer errors resulting from the 37" tires ??

If not, your indicated 82 MPH is actually closer to 95 MPH ... takes a LOT of HP to make a brick fly at 95 MPH.

 

[FJtest]

Pretty much the same here. Off-road, on-road, back roads, in town, on the highway. The only time I typically get lower gas mileage is on the highway at higher speeds. My 35s on stock gears like running 90mph in 6th gear. Seems happiest there, despite the protest from the falling gas needle.

What engine RPM are you seeing with 35's at 90?

 

[FJtest]

Had to run to a job site today. 2725-2750 rpm at 90mph.

Probably gonna lose some face here, but I've got to admit that I've never seen 90 on my speedo.

 

[FJtest]

I have kept track of miles per gallon (MPG) my last 14 tanks of gas - similar to you I put 15ish gallons in each fill up. I always run 87 from Sam's Club unless otherwise noted below. My FJ is basically 100% stock, 2012 with Convenience package and Off-road package, 110k miles.

19.86
17.78
19.44
19.15
18.18
19.79
16.57 (camping trip - more off-roading)
19.49
19.76
20.38
16.79 (Costco gas)
17.67
18.97
19.26

Roof rack, or naked top?