Noobie MPG question

I apologize for my asking such a simple question but my mechanical knowledge is limited but I am learning. Learn as you go right? I am wondering besides air intake and exhaust, what are other ways of improving gas mileage? I am getting around 13-14 mpg and would like to increase that. I read of people getting 17-19 mpg and as much as that doesn't sound like a lot, as much as my XJ gets driven, I am having to fill up every 2-3 days. Any advise would be great. Thanks

Chuck

keep your foot out of it, make sure all tune up, oil change and such are done and that's about it. It won't ever be great, not with cinder block aerodynamics.

new plugs (gaped proper .035 i think) oil change keep it well maintained. my jeep is a dealer baby for the most part and i get about 17 on a flat surface. if you dont wheel much pull your front drive shaft, and use little skinny pedal. MPGs in a butshell

Always post the year/engine, but from your name, assuming it is a 2000?

New plugs are critical. Gapped properly!

A bottle of a quality fuel system cleaner (BG44K, Techron, etc) is never a bad idea as it helps the fuel injectors optimize their spray pattern.

Replace your air filter if it is dirty. Often overlooked.

Fresh fluids all the way around. Oil, coolant, transfer case, differentials, transmission.

You should be able to get to approx. 16 city, 20-21 highway if the engine is working efficiently.

Be sure that you are "calculating" your mileage correctly. You must do the math. Miles driven divided by gallons consumed. Any other way may not be accurate. Keep a small notebook in your glove compartment and keep a rolling record of your mileage at every fill. Takes all of 1 minute and is a good snapshot of how things are going.

And if its a 2000,don't bother with any intake/exhaust mods,you'll be wasting your money.

Also, verify just HOW far off the odometer is. My 98 reads 3% on the low side verified by mile markers on I-25...

Not trying to discourage a new discussion but there are extensive threads on this question that will help. Look in Street and Performance Forum for a current thread that is up to six pages. Never hesitate to join in with your questions and comments.

As the others have said, but I would add use synthetic lubricants in everything, run your tires at the max psi you can without causing excessive wear to the tread in the center of the tire.

wow those are low MPG's! I get about the same in my 5.9L Grand Wagoneer

I get 18 driving like a granny, and ill get somewhere in the neighborhood of 13 if im on the gas a lot.I run all synthetics and do the usual tune up. BTW if you get new plugs Id just get the champion plugs, the 4.0L doesnt seem to like expensive plugs very much. Ive tried running some iradium plugs and the regular champion plugs do better than the iradiums.

birchlakeXJ said:

Be sure that you are "calculating" your mileage correctly. You must do the math. Miles driven divided by gallons consumed. Any other way may not be accurate. Keep a small notebook in your glove compartment and keep a rolling record of your mileage at every fill. Takes all of 1 minute and is a good snapshot of how things are going.

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That's the biggest part that most people screw up with their 'calculations'. Make it simple, or build it out if you need. I kept a small notebook for years that had the mileage at fillup, gallons added, and maintenance details. Calculating mpg is as simple as (new miles minus old miles) and dividing that by the number of gallons added. It's discouraging when you read some of these threads and you see how screwed up some people can make that.

Don't drive like an asshat.
Keep your foot out of the gas, and maintain a steady speed when you're driving.
Pull all the crap off the roof that isn't helping get you to your destination (rack, spare tire, shovel, Christmas tree, etc).
You're driving a box with the aerodynamics of a brick, so don't expect econobox mileage.
Maintain the vehicle, so rotating parts rotate with less friction.
Proper tire pressure is essential.
Read the other threads on better mileage here. Assuming you've got a 2000 (4.0L?), you already have a pretty good motor to start with for mileage. Improvements are going to give you incremental improvements, that a stiff headwind will erase. If you want Honda Civic mileage, get a Honda Civic.

Jim www.yuccaman.com/jeep

Funny. As you can see from my sig, I have three 4.0 powered jeeps. The 97 XJ with an auto, 160k miles, gets the worst mileage of the 3. Even assuming the odometer is 10% low because of the 31" tires doesn't get it much above 12 MPG. The engine uses very little oil. Most of the fuel injection electronics are new. It has a CAI.

I can still get 16 MPG on my 90 with 33's, and all kinds of weight adding stuff. The WJ if the plugs are changed every year gets 16-18 mpg in town, and 20 on the highway. I don't expect the 97 to get real mileage, I do have a Honda for that. But I don't see why it should get 11 mpg in town.

It's puzzling to me. Only two things I've thought of is to change the MAP, and fiddle with the tranny linkage. It does seem to downshift more than I would expect.

Manual and gearing. My 92 with 3" lift, 4.0l, 5sp, on 235/75s gets 18mpg consistent with city/hw mix, 20mpg if it averages above 80F. With an auto, I've personally never known someone to get over 15mpg hw.

My RENIX will get as much as 24 on the highway but the newer XJ's that I have can't touch that. The 2000 is the worst, its in perfect condition mechanically and only gets 18 on the highway.

Just for a comparison, my 2009 Hemi Commander gets better mileage than my XJ's, I get around 20 on the highway with 380hp to have fun with.

I still like the XJ's better though!

My 88 with 30's and 345,000 + miles on it gets around 14-15 on the highway, and 12-13 around town.

My 96 with a 3" kift (stock tire size tho, got it that way) and 160,000 on it, gets over 20 on the highway, and haven't used a full tank yet city driving.

Normal maintenance and sensible driving will get the best mpg.

Swamprat said:

new plugs (gaped proper .035 i think)

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.035 is correct for a 2000.

Something I'll add to this: distributorless (meaning: 2000 and 2001 XJs with the 4.0) seem to be more sensitive to plug gap and type than earlier models. That's not to say that it isn't an issue on earlier ones, but in my experience being out by as much as 0.003 can give a noticeable difference.

Right now I've just swapped out some 10,000-mile Bosch Supers for NGK V-Powers. The Bosch plugs were good and clean, but comparing their gap with the NGKs (both of which were measured out-of-the-box but not adjusted) showed that the NGKs were just ever so slightly closer than the Bosch units. Granted, plug gaps can go out of adjustment over time, but the difference was consistent across all six plugs which leads me to believe that there are likely some manufacturing tolerances at play here. Time will tell if there's any improvement, but based on past experience I'm anticipating that the NGKs will be a better match.

I've played around with different types of plugs at various times, and have come to the conclusion that on a distributorless model with a stock or mostly-stock engine (meaning: 87-octane pump gas, no internal changes, maybe an FIPK or upgraded injectors), just use the standard OEM-recommended plugs. Even if 'better' plugs aren't causing any subsidiary issues such as poor fuel economy or running, there's no sense in spending even a few extra dollars on them if there's no noticeable gain.

All that aside, the recommendations made above are pretty much spot-on. One thing I'll add to them is fuel injectors. I recently swapped out my decade-old OEM units for 0280155917 injectors, and have seen about a 1mpg improvement across the board; YMMV. There are other maintenance considerations I need to take care of (tranny flush being one of them; it's overdue) that could possibly result in further improvements, but given that probably 90% of my driving these days is around town, getting 14.5mpg vs. 13.5mpg is a definite improvement.

fattmann said:

Manual and gearing. My 92 with 3" lift, 4.0l, 5sp, on 235/75s gets 18mpg consistent with city/hw mix, 20mpg if it averages above 80F. With an auto, I've personally never known someone to get over 15mpg hw.

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I typically pull 21 with highway only, and 18-19+ in combined commute mileage. 1991 4.0, auto, rolling on 30's.

The 97 XJ 4.0 and the 99 WJ 4.0 both have autos. Both are well maintained. Weight difference, meh. Yet the WJ averages 4 MPG more. I do think the WJ's 4.0 runs better, the factory does rate it at 5 HP more than a comparable XJ engine.

My experience with the distributorless ignitions is exactly the opposite of casm. When I first changed the plugs on the WJ after buying it at 50k, the gap was .080. New plugs made no difference in drivability, and maybe .5 MPG. I was shocked when I measured the gap on those plugs.

I'm fairly good at tuning cars. I got 21MPG with my 67 Buick LaSabre with a 340 two barrel and two speed hydromatic. This during the first oil crisis when I thought driving from AZ to San Diego to San Fransico to Seattle to Chicago was fun.