Gas Milage, Engine Rebuild or Swap

[JeepGhost]

I don't know if this is the right place for this or not, so move it if need be.
Jeep:
1995 Jeep cherokee XJ
4.0 inline six
Manual AX15 transmission with the NP 231 transfer case both from Novak conversions in 2015 or 2016
Has approximately a 4 to 4-1/2" lift with a rear swing gate bumper/spare tire mount
Manual hubs
sits on 31's

First off, thank you to all, I've used this forum for years for info and it has helped.

Now, my question.
My engine has well over 300,000 miles on it and it is tired. Can't afford a new car as a daily, so, I am looking at two options.
I would like to start to get my gas milage up from the 16 to 17 mpg range up closer to 20 or over. My pipe dream would be the upper 20's, but, probably not possible.

I am looking at two options.
A) rebuild the engine.
B) do an engine swap into something like a GM V8 ls. Probably the 5.3l

Does anyone have real world experience with this and if so, what were your results? I won't really be starting anything on this until July, I am doing research and decided to reach out to see what I feel would be my best option based on input from those whome have done this already.

Thank you.

 

[Unclewolverine]

A stock four cylinder 5 speed is doing good to break mid 20s. If you are getting 16-17 with all that you are doing better than most. I average 15 in a bone stock rig with half the miles.

 

[Anak]

A stock four cylinder 5 speed is doing good to break mid 20s. If you are getting 16-17 with all that you are doing better than most. I average 15 in a bone stock rig with half the miles.

+1

Rebuilding your 4.0L is not going to get you into the 20mpg range.

An LS swap may get you there. That is probably the direction to research. I don't see your location, so make sure you don't have legal hoops to jump through, or at least know what they are and be prepared for them.

 

[Goose_XJ88]

I can shoot a message to Clydefrog who did a 5.3 in his 87 almost 10 years ago now. Biggest thing is where are you located and how much time do you have for down time? Location because its stupid on how difficult it is to be smog legal in CA (if not impossible now-a-days)

You mentioned no alternative daily so curious what your plans are for the rebuild or swap. I think the swap was around $10k and I know most Strokers are in the same ball park so it might be more feasible/cheaper to find a $5k beater to daily.

 

[clydefrog]

When I originally did my swap I was on 31" tires and 3.73 gears and averaged around 20-21mpg. Keep in mind you WILL have a heavy foot, the LS in the XJ is super fun. I currently have 33" tires and 4.56 gears. I have a Yakima roof rack and on a bad day I will get 18mpg but I'm mostly in the 20mpg range. I did my swap at 297k and I now have 335k on it. I have driven all the way to Canada and to Moab Utah with it so its way more reliable. Easier to find parts for a truck 5.3 too. I was around $10k but that was in 2014 and mine is CA smog legal which adds substantial $$$ to the swap.

 

[75SV1]

My '88 MJ 4.0L 2WD got about 23 mpg on the highway. I've heard one or two report more. I've heard the same on some XJs. I'd have to drive them to believe it though. I did have an '98 with about what you are running. I'd get around 17 to maybe 18 highway. I think 14 to15 local driving. I had a '98 stock. Usually, 18 to maybe 20 mpg highway.
I do have a 2000 XJ. Metric 31's so basically 31 - 9.5, 2 inch lift and 3.73 gears. I was getting about 17.5 mpg, maybe 18. I did some upgrades along the way. Mainly, and electric fan. No MPG increase. Then I did three things: window deflectors, rear quarter cut and fold, and changed the front diff oil to synthetics. I went to 19.5 to even 20.5. The motor had around 280K on it, and a piston making noise. The skirt cracked on #6. I haven't run it much on my mini stroker yet.
There was or is a thread on Jeep.com on fuel milage. Charlie33, he claimed 23.5 mpg. Did a lot of work on a very clean '99 XJ. Lifted 3" and 31's. Also, another thread that did aero mods. claimed 27 mpg. I haven't tried them yet. Bumper and front grill.
I am doing an LS swap. Its been a long process as usual for me. Yeah, some $$$. Also, I don't think there are many of the low buck donors around. I've only heard of two other milage reports than the one above. One was on an MJ with manual trans, 17 mpg. Another was 26 mpg. Again, I'd have to drive that to believe it.

 

[JeepGhost]

Thank you for your replies. I am in Washington state.
I'm not starting anything serious until after July. For alternative transportation, I may be able to borrow a work truck, so yes, it is on my mind. Thank you

@75SV1. I will concur your mileage on an 88 xj. I had a 4wd 88 with the rennix system and got about the same. The only difference is I had larger tires. 235/75/r15's I think. It has been a long time since I had that jeep.

 

[75SV1]

Mine had the larger stock tires or the 225's. It was actually reporting 25 mpg. Mine was a manual B-10/5 trans. Also, I think someone put in a 3.55 rear end. I still have the MJ. Another build out in limbo though. If you plan to rebuild your 4.0L, I'd look into a stroker. Some say the Long rod strokers give +2 MPG. I'm looking at Cleggs Stage 2.

 

[Goose_XJ88]

On one of my latest acquisitions (91 XJ 143k miles) I had 33s, 6" lift, 3.55, XO Fab Cage and clocked 20-21mpg on the freeway going 65/70 on all flat land. This was on the only trip that I have taken it on though.