Top Ten List - Maximum MPG

What are the most effective maintenance tasks or modifications for our XJs to maximize fuel efficiency? A checklist would be great.

Leave it STOCK, and give it a tune up Keep the skinny stock tires. Inflate tires to what is posted on the door jam. Follow the OEM maintainance schedule. Put in no greater than 30w oil. Most stock XJs were capable of 20-24 MPG hwy depending on whether they were Auto or Manual.

Virtually everything else negatively affects the MPGs with the exception of lowering it or dropping in a diesel.

Once you make the appearant size of the brick bigger, and/or put on larger tires, you start down the slippery slope to Gallons per mile

-Ron

Buy a Honda

Hey i get 20MPG with mine.That to me is great for a toy

I am running 31x10.5r15's and get 20ish (as high as 22) on the interstate with 3.07 gearing. The majority of the mileage gains came from a tuneup, 703 injectors, and making sure I had a forward rake in suspension height.

There was a guy on eco modder who did a bit of aeromodding on his xj, basically a thin steel belly pan. He claimed 30mpg iirc, mostly stock

WB9YZU said:

Virtually everything else negatively affects the MPGs with the exception of lowering it or dropping in a diesel.
-Ron

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I went the diesel rout on my ZJ.
http://www.canev.com/cherokeeConversion.php
Amazing improvement on fuel economy.
Why diesel are shunned in North America is beyond me.

I bought a civic and my mpg went from 11 to 35

I'll average 18 on the highway.. not bad for 3"/31 tires on stock gears.

How many actually adjust their claimed mpg when running larger tires and stock gears? If your speedometer is off, then so is your odometer.

If your speedometer reads faster, then your odometer will turn faster. First determine what % your speedpmeter is off and then adjust your total mileage by the same percent. Now you can figure your true mpg.

^^ Not many.

I switched my speedo gear and actually it still reads a bit slow against my GPS. I'm about 1-2mph off at 30mph. It gets worse the faster I get. So whatever mpg I calculate, I know its better due to that.

I top off, drive X miles, top off again and divide to get MPG. Speedo hasn't worked in years. then run sensitivity analysis on the actual miles traveled, and throw in some other variables like frequent stops, etc. get a way better idea that way.

I've tried for 6 years to have a balance of capability and mpg... I can't go back from 4.56's, nor can I take my long arms off because I hacked the stock mounts off. Nor do I want to ditch my heavy armor which saves me on the trail.

I daily drive an 04 grand cherokee, with 32's, a 3 inch lift... And a 260 hp/330 ft/lb high output 4.7... It gets 5mpg better than my cherokee.
The 4.0 just sucks fuel.

evguy1 said:

Why diesel are shunned in North America is beyond me.

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Oldsmobile 350 diesel.

I'd love to buy an older XJ (so it would pass emissions) and swap in a small NA mechanical IDI diesel. Wouldn't be fast, but reliable and run on practically any fuel and get good mileage.

I'd be interested to see if someone that runs ethanol free gas gets better mpg. IMO that has a lot to do with the 1-2mpg I randomly lost 4 years ago.

I've used Lucas fuel injector cleaner/upper cylinder lubricant for a while now, I usually buy a bottle a couple times a year. Doesn't ever seem to help unless it's really needed. I'm trying MMO right now, the 3oz per 10 gallons rule that is well known on the internet. I don't have any data to report, but I record my mileage in a log book often so I will be able to see if that actually makes any difference.

Wow, I'm really surprised by the rational, realistic responses folks are giving. Good for you guys being honest.

I've seen serious discussions before that had one individual (who will remain nameless) actually claim that his XJ with 35's, enough lift to fit those 35's, and 5.13 gears was the mileage champ at 25 mpg!

Let's face it, XJ's with mods suck fuel. But they still do better than TJ's!

The best thing I did was buy an Integra GSR. Made my commute 100x more fun and got 30mpg no matter how I drove it. DD'ing a Jeep sucks. I didn't learn my lesson and now I'm doing the same thing with a lifted WJ.

If you have no choice, leave it stock and keep up with maintenance.

I love DDing my Jeep... but its still pretty tame.. I had a civic hatch... by the time I paid insurance and crap, the fuel savings was not worth it. My commute is 3 miles.

I'm building my Jeep to be a compromise of both worlds.. offroad and DD.

DerMeister said:

I'd be interested to see if someone that runs ethanol free gas gets better mpg. IMO that has a lot to do with the 1-2mpg I randomly lost 4 years ago.

I've used Lucas fuel injector cleaner/upper cylinder lubricant for a while now, I usually buy a bottle a couple times a year. Doesn't ever seem to help unless it's really needed. I'm trying MMO right now, the 3oz per 10 gallons rule that is well known on the internet. I don't have any data to report, but I record my mileage in a log book often so I will be able to see if that actually makes any difference.

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It depends. As much as I hate that as an answer.

I can get ethanol free 91 here. I tried running it and mileage went down. The low compression 4.0 and the computer on it just isn't able to handle the 91 octane and gas went down.

The jeep did idle and run smoother on the 91 ethanol free.

Still trying to find 87 ethanol free around here. I can get it at an Indian reservation about 30 miles away ... but not exactly convenient to drive 60 miles round trip for gas.

I suspect the 87 ethanol free will give much better gas mileage.

Two weeks ago, I went from 11-18.5 by doing the following:
-Ditched ZJ fan clutch for "normal" fan clutch
-Switched from Rotella T6 to a 5w-30 oil
- Aligned it dead straight with no Toe-In at all. It wasn't toed in that much at all, but every little bit helps.

Ethanol, my old man claims, is good for a 1% drop in fuel economy per % of Ethanol in the gas. I don't think this carries in to flex fuel vehicles but yeah, I notice a 10% drop between ethanol and eth-free gas.
I average 16 in mixed driving, have seen as high as 21 mpg on highway. Thats stock gears & 235 series tires. I tried mods like cold air intake, exhaust, injectors, electric fans - none of it made a damn bit of difference that I can tell. Then again, around the time I was trying to squeeze mileage out of the Jeep, I was driving under 3 miles to work and going through about a million stop signs and signals on the way.
As with any vehicle, best MPG mods you can do are basic maintenance. Plugs, wires, cap, rotor, air filter, keep the injection system clean.
I dunno... I may have picked up as much as 2 mpg with the above mentioned mods, but I tend to discount that since around the time I put some mods in I changed my driving habits (season changed, I was on my bike, car got driven further per trip & no defroster).
Anyway.
There's no magic bullet(s). The XJ slurps gas. Gear it right for the tires you've got, open up the airflow for the extra power (don't hope for MPG and you won't be disappointed) and enjoy the fact that gas-hog or not, it's paid off.