Rusty-J Got Some upgrades and now has poor gas mileage

Hey guys! Ive got a 91 4 door Cherokee that I picked up in Canada a cpl years back on a snowboarding trip. (Beats renting a car) None the less fast fwd to a trip this past June from SoCal (Joshua Tree) > Moab, Utah. While driving through NV it was nearly 120 degrees outside... And the tiered stock radiator, water pump and mechanical fan were not up to the task. I enjoyed the entire week and nothing broke as long as babied it pulling off to let her "cool down". I finally saved up the money and bought a a new thermostat, water pump, aluminum radiator, 3 electric fans, and the aftermarket probe style sensor.

I ditched the mechanical fan (for the reasons above) and went with the aftermarket NAPA temp switch because I could dial it in to match the thermostat I purchased. I looked and looked and could not find any factory style switch because my jeep is a non a/c Canadian version (I was told) Here is where things get confusing to me...

Jeep run's beautiful, fans kick on when it hits gets to temp. For Christmas we decided to drive the jeep up to our Cabin in B.C. Canada from Joshua Tree and it went from getting fantastic gas mileage (pre-new cooling system) to the worst out of any vehicle I've ever owned. I mean went from nearly 400 miles per tank of gas to less than 225 miles per tank of gas. I was so paranoid I maxed out my valaro card on the way up north because I didn't want us to be stranded on Christmas with my AAA card maxed out on tows and emergency gas. Ive got no check engine lights on, and the jeep still is running great no fluctuating on the idle and no check engine lights. Threw a new k&n in, fresh oil change, new plugs & wires and still no improvements on mileage. Got over 1k in cooling system & tune up and still ****ty mileage all in the name of not over heating on this years Dirt N Drive trip to Easter Jeep Weekend. Any advice before I throw more money at what used to be my cheep jeep XJ project. Ive been told there are two coolant sensors that could be changed or the O2 sensor... But really cant afford to throw anymore money without some sound advice.

Stats: Its an Automatic, 4.0 6cyl. No A/C, NP231, 6.5 inch lift, 33inch BFG AT's, HI Pin Dana 30 in the front, Chrysler 8.25 in the rear. Has a Flex a lite radiator, 3 electric fans and the quadratec water pump

Lunghd.com has some info on how to test sensors and such.
But pending how many miles on the jeep, and if/when O2 has been changed it might be time for that.
Aside from that, I recommend running some BG44K in your tank and some Seafoam or Berryman's B-12 in your intake, and clean your TB.
But, it also sounds like you are running 33's on stock gears which doesn't help MPG at all.

I'd also suspect a clogged cat

Thanks Johnny & Trippled,

I've ran a few things though the tank (lucas injector cleaner and the Royal Blue Mileage treatment) But I guess i'll give your chemicals a try and pick up a new O2 sensor on payday. I have a magnaflow catback system on it but its still got the factory CAT so I guess its time for me to save up for that to be swapped too. But as far as gearing goes, this is the second XJ Ive ran with 33's and got good mileage with... The concerning part or coincidence to me is once I installed all the new cooling system parts right before Christmas it literally was like turning a button for fuel economy off LOL :repair:

Have you rechecked your work on the install of all that new stuff? You could have knocked some wires loose, especially the O2 sensor.
You can do a vacuum test to check the cat. No need to buy one 'just in case.'
You should also do a code scan and real time diagnostics using the OBD-I interface near your ECU. I know O'Reillys has the bosch scanner you can use that will attach to a 91.

You talk about this new thermostat and controller to match it.

That thermostat is 195* yes?

if its not, it will kill your fuel mileage. The computer wants to be at 195 and will keep the engine running rich to warm it up to 195 until it gets there.

That's what I was thinking, temp has everything to do with mileage!

400 miles per tank on 33's and stock gears? I want that jeep.