I, too, never understand the numbers I hear sometimes. I am running a 5.5" RE lift now -- closer to 6.5" -- a winch bumper, Smittybilt winch, a Hi-Lift hanging on the front, and fairly aggressive 31X10.50s -- going to 35s soon -- and I NEVER see under 24mpg on the highway! I have Neon injectors, a Banks header and a cold air intake, too, btw. I also have an AX-15 trans, and the gearing was changed from 3.07s to 3.55s, which actually improved the MPGs. Before I did the lift and was running street tires, I seen a best of 30.16mpg -- GPS confirmed. I also run a Scan Gauge II, which has helped me to modify my driving habits even more.

 

This feels like the twilight zone. A mostly civil discussion (online) about Jeep mileage. So weird.

This is the first mpg thread I've ever seen where less than half the responses are NOT "get a prius" .

That said, I just lifted another 2" to 6.5" long arm. We'll see if this has any effect on my average 22mpg.

I always suspect that gearing has a lot to do with mileage, but of my 6 XJ's ranging from bone stock with 3.55 gears and stock tire size, to my many 4.5" with 31x10.5 and roof rack and no air dam, everything seems to get around 22mpg. My ex's XJ (that I gave her) is a bone stock 98 as well, and she came to complain to me recently that her mileage has "dropped" down to "ONLY" 550km per tank (fuel light comes on).

As for cracked header. Eyup. That'll make a holy**** difference in your FE. I cracked mine on my 90 and went from 24mpg to abut 12 in one shot. Mileage that poor I always start with O2.

Also, I always have my OBD data streaming to my phone with one of these:
http://dx.com/p/elm327-bluetooth-obd...r-dongle-16921

Steaming data to Torque (on my Android handset):
https://play.google.com/store/apps/d...l.torque&hl=en


Completely changes how I drive (for the better/moreboring). Can't go wrong for $30 shipped.

 

For my 1990, it's on the engine block. I don't know about newer models without opening my manuals. My coolant temperature sending unit (silly autozone calls it a temp switch...) is on the back of the cylinder head near the firewall. So happy that others on this forum corrected me and clarified the difference between the 'sensor' and the 'sending' unit, as I didn't even know there were two, in addition to the fan switch on the radiator (for my 1990). In any case, what I've been able to glean from the forums and google, the temp sensor is extremely important for the computer to know when the engine is at operating temperature, else it thinks it's running cold.
Hope this helps.
(I got a 'wave' on the street yesterday from another cherokee! Awesome!)

 

Up until the 1997 model year, the ECU/PCM used a separate sensor from the dash as you describe. Basic dash models had a simple switch instead of thermistor. Starting for the 1997 model year Chrysler only used a single sensor and based the dash gauge off of that. Way more obvious when there's a problem.

Nice. I've concluded that XJ owners here are armless

 

Yeppers. Bought me a new "temp switch" and tried to change it out today. That one that's on there now, the plastic broke off. It's only held in place by a piece of metal used as the conductor. Anyway, key word TRY. I just can't get in there without taking off the valve cover. Part of the cover covers part of the sensor! Unless I'm seeing it wrong. Did you take off or loosen your cover to make the switch?

If I'm not mistaken, the ECU thinking the engine is cold makes it run rich, right?

 

Correct