Improving Stock Gas Mileage

[ihscoutlover]

I own a '94 XJ 4.0 HO, AW4, with 235/75/15's, what can I do to improve some performace, and pick up some on my gas mileage?? Thanks


Jeff

[Mikel]

Get a little 4-cyl car?

There is only so much that you can get from a boxy vehicle with a 4L engine... My 95 gets 21 now and that's as good as it's ever been.

[scorpio_vette]

how in the world do you get 21mpg??? my best ever was barely 19, and that was on a 3 hour highway ride with cruise control. around town i was lucky if i got 14, and now i'm down to 12.

[Mikel]

Bone stock 95 4L/5sp, 206K miles. Most of my driving is highway, usually around 70MPH. I replaced the O2 sensor and gained an extra 30 miles per tank.

how in the world do you get 21mpg??? my best ever was barely 19, and that was on a 3 hour highway ride with cruise control. around town i was lucky if i got 14, and now i'm down to 12.

[Kejtar]

Got a roof rack? dump it. Got roof rack rails? dump them (just cover the holes up though). Drive slower when you can (no cruising @ 70). Unload all the extra junk that you carry so that the rig isn't too heavy. Oh and don't forget to wax it every week for better slippage through the air :D

[UNCC_99XJ]

You could start with a Tune up (plugs, wires, cap & rotor). Unless it's already been done, drop a new air filter in it ( I don't buy into the K&N drop in's....but several on here do and like them).

I've got a 99 4.0 auto 4x4 and Get roughly 14-15mpg all city. I used to get AT BEST 12, untill I did the above. Also switched to Mobil 1 10W30 Synthetic and noticed about half a mile per gallon increase, as well as a better running engine. Also remember you're in a 2 ton (assuming 4x4) brick with wheels. It's not an escort, and it's not got the handleing of a Ferrari, so don't race the crap out of it. Drive sensable and you'll probably see an incease. I try not to rev it over 2500 when possible.

Couple other things you might consider, I leave my tranny in "3" rather than "D" when I know i'm gonna be under 55 for my trip. And extreme short distance driving is murder on mpg, as well as your engine. Try to avoid it when possible.

[langer1]

I own a '94 XJ 4.0 HO, AW4, with 235/75/15's, what can I do to improve some performace, and pick up some on my gas mileage?? Thanks


Jeff
First things first, whats your mileage now?
One thing found is during cold weather is getting rid of the K&N cone filter and going back stock box with heat riser will give you 5 mpg back.

[CharlesS]

When I first purchased my 98; I took a trip to the Grand Canyon and received 23-24 mpg during parts of the trip, but that was then.....
Now with all the off road armor and performance modifications... I get 16 hwy on a good day...
MPG/Performance modifications consist of Gale Banks header, Gibson catback exhaust, MSD-6a ignition w/coil, MSD Superconductor 8mm wires, JET Stage II chip, K&N FIPK, TurboCity throttlebody, all synthetic lubricants.....

Charles

[XJHummerRescue]

Man, I get about 16 city with my '89, and thats with a lead foot :).
The '92 also gets around 16 city and the '95 gets around 17 in the city.

The '92 and '95 are bone stock and the '89 has a 2.5" exhaust and a huge K&N conical filter.

[Rufio]

im gettin about 10mpg haha with non leadfoot, in my 88 waggy limited 4.5 inch lift on 33x12.5's non regeared

[reddragon72]

I cannot believe no one mentioned the contraversial finger nail polish remover :)

Oh and I get 17 on 240,000 miles with 2.5 exhaust and K&N filter only mods. Yea its a brick on wheels and I love it.

[BSD]

I cannot believe no one mentioned the contraversial finger nail polish remover :)


O.K. since you insist... the best thing you can do to improve your mileage is to add acetone to your gas. :roflmao:
BSD

[langer1]

My 87 get 18 city 21 hy in the summer and 23 with 1oz of acetone per 10 gal.
Winter drops to 16 city 19 highway acetone don't seem to help mileage in temp below 40.

[iBran]

Couple other things you might consider, I leave my tranny in "3" rather than "D" when I know i'm gonna be under 55 for my trip.
What is your reasoning behind this? You wouldn't limit yourself to the first 3 gears in a stick-shift, would you?

[otto]

You wouldn't limit yourself to the first 3 gears in a stick-shift, would you
No, to the first four gears. Overdrive is for sustained highway speeds.

[iBran]

No, to the first four gears. Overdrive is for sustained highway speeds.
Yes. However, there's absolutely no reason to put the transmission in "3" unless you need engine braking (or, unless your tranny is borked and shifts in to 4th at the wrong times...)

Normal driving = put it in drive.

[montanaman]

The acetone thing is interesting. I've never heard of that before. There seems to be some conflicting evidence on the net about it. Many people saying they tried it with better gas mileage as a result.

Lots of other people saying it's hell on plastic and butyl rubber (which I know to be true).

It seems that the key question is this: if you add only 1 oz. per ten gallons of gasoline, that represents less than 1/10th of one percent. Is that a strong enough mixture to do harm? I dunno.

So far, I haven't been able to find any posts of people saying they tried it and had bad results.

[BCKNBLK]

Weight is a big killer on your mileage. Take out what you really dont need. Always stay on top of your tire air pressures, especially if you live in a very seasonal state like mine. Drive conservatively, find your jeeps sweetspot as far as the rpm's go, for highway driving and stick to it, even if you have to ride the right hand lane. And always keep the engine tuned up well, especially those who have the older models that still have the distributors, spark plug wires and such. I have an '01 so theres not much to change on a tune-up anymore, but I stay on top of all the above mentioned, and I religiously keep a mileage log, and I get an average of 23 mpg.

[torfinn]

Also verify that the lockup is working on automatic trans. Driving style is what affects mileage the most. O2 sensor should be changed at set intervals, and would affect mileage as the sensor wear.

regards
Torfinn

[RTicUL8]

Helium in tires!:thumbup:

Breathe it too right before you drive:confused1

[UNCC_99XJ]

What is your reasoning behind this? You wouldn't limit yourself to the first 3 gears in a stick-shift, would you?

I've always been taught and told that just because you get your engine to turn at the lowest rpm's possible (in this case, leaving it in D and letting the OD kick in), doesn't mean you'll get your best mpg out of it. It's about how well you use your your available torque and HP together. To me, in my experiments, my XJ with the 4.0 seems happier around town when I leave it in 3. Most of my speeds are under 55, and if I do go over that magic 55, i'll kick it up to D and let OD kick in. And as mentioned, you're still using 4 gears, just eliminating the OD portion of 4th for the time being. And In the straight drives i've driven, I've done the same thing, leaving it in 4th untill when i'm under 55 sustained.

On the acetone subject, I tried it in both Jeeps....my XJ and my moms KJ. In my XJ I noticed a gain of about 1.5mpg, and in the KJ about 2.5mpg. Both get about 14-15, all city driving. Once winter kicked in I quit using it as I also noticed little to no effect when the temps were under 40. To transport it to the gas station I use an old snapple bottle I found in my recycle bin, filled it with 2oz. of acetone (using a glass measuring cup), and marked a line with a sharpie for easy reference in the future.

[ihscoutlover]

Engine has about 35k on it, the t-case has about 6k on it and the rest of the XJ has 190k on it. I have put synthetic in the front diff, and t-case and am considering it in the tranny and rear diff. Would it benefit me to put a FIPK from K&N in or a header or what?? I have about 5k on the tuneup, that didn't include wires, but am planning to get those in once I get the jeep out of the repair shop.(Rear springs, motor mounts and tranny lines) I am going to check out the brakes and calipers here in the next week and am just wondering if I might be missing something?? I just put on the 235's and just plan to use as a daily driver and was curious if I could squeak 20mpg out of this thing and if so what should I do. Thanks for your replies.


Jeff

[montanaman]

Well ... I found only one reliable test of acetone as a fuel additive.

Kettering University did a controlled study on regular gasoline in a Buick V-6 motor mounted in a test stand, and ran it under varying loads and conditions (programmed into a computer).

They then repeated those exact same conditions (same computer program) with acetone as an additive.

Unfortunately, they got pretty much no difference with acetone.

So far, this is the only tightly controlled test I've been able to find, and it doesn't look very promising.

Here's the link: http://www.kettering.edu/news/archivedDetail.asp?storynum=406

[Cherikon]

Somethings that I have found useful for improving gas mileage:

1) Seafoaming the engine (via the throttle body)- removes carbon build-up

2) Upgrading plugs/wires/ignition coils.

3) Using the right grade of oil for the season- thicker oil in summer and thinner oil in the winter.

4) Change up your driving style- don't drop the hammer everytime you have to go somewhere, don't brake hard- it wastes energy.

5) If you are running a mud terrain switch to an all terrain- less rolling resistance and more stable tread pattern

[SS01XJ]

Somebody try one of these things and give us a full report. I don't want to try it;you try it; better yet, let Mikey try it.

http://www.savefuel.ca

[zthang43]

Well ... I found only one reliable test of acetone as a fuel additive.

Kettering University did a controlled study on regular gasoline in a Buick V-6 motor mounted in a test stand, and ran it under varying loads and conditions (programmed into a computer).

They then repeated those exact same conditions (same computer program) with acetone as an additive.

Unfortunately, they got pretty much no difference with acetone.

So far, this is the only tightly controlled test I've been able to find, and it doesn't look very promising.

Here's the link: http://www.kettering.edu/news/archivedDetail.asp?storynum=406

Hey, that's where I went to school! Prof. Davis (mentioned in the article) is a pretty smart guy.
Something else I learned at Kettering was that wind resistance is the biggest force pushing against the car at higher speeds. This is a graph of road load (horsepower required to move the vehicle at a specific speed) and rear wheel horsepower for my 91 XJ with the 4.0/AW4:
http://i24.photobucket.com/albums/c26/zthang43/Jeep%20lift%20kit/RoadLoadCherokee.jpg
As you can see from the dark blue curve, the road load at 70mph is ~50hp, but at 55mph, it's only about 20hp.
This means that your engine has to put out 50hp to go a constant 70mph. (Keep in mind that this is calculated, not measured, data, and will vary quite a bit depending on how each xj is set up with tires, roof racks, etc.)
My point here is just to show how you can save gas by going slower (although I hate driving slow), since the engine won't have to put out as much power to keep you moving.

Anything you can do to cut down on wind resistance will help, including (gasp!) running small tires that are tucked into the wheelwell as much as possible. (lifting your jeep will increase the wind resistance even without bigger tires, because air flow through/around the wheelwells is affected.)

Of course, engine efficiency and all that good stuff comes into play when you talk about whether it's better to drive in 3rd or 4th gear; tire size and gearing will contribute a lot there.

So, (hopefully I don't get banned from NAXJA for saying this :) one of the best ways to get better mileage out of your xj is to take off the lift and put the stock tires back on. I'm not saying you should do that, but you did ask.

[djblade311]

buy one of those Tornado air vortex thingys...haha. j/k. I too have been having fun trying to improve my MPG, I replaced both o2's, LiveWire plug wires, screamin demon ign coils, K&N FIPK, Stage 1 Jet chip. It was getting bad MPG before and it has only helped by 1 or 2 MPG.

[Cornflake]

I just follow behind big rigs, whether they are going my way or not. It's called drafting........:)

[montanaman]

My point here is just to show how you can save gas by going slower (although I hate driving slow), since the engine won't have to put out as much power to keep you moving.
yeah ... wind resistance increases as a squared function of speed, so if you double your speed, you quadruple your wind resistance. Above a certain speed, it makes a big difference. At low speeds, the wind resistance is negligible, but at higher speeds, it gets out of hand.

I've thought of trying to mount an air dam up front (below the front bumper), to improve the aerodynamics. Those things have been shown to really improve gas mileage at highway speeds. The only downside is that on a jeep, you would have to make it removeable, so that when you go offroad, you don't smash it to bits :). Kind of like the quick disconnects on the sway bars.

I'm also running 225/75-15 tires, which make a big difference, I believe.

Smaller effects can be had from synthetic fluids all throughout, an efficient wiring system to make your alternator work less to pump juice through the wires, and keeping your junk (extra weight) out of the back.

[dj's 2000 xj]

I have added a 1" spacer to the throttle body on my 2000 4.0. Just a billet spacer, no airaid, and I noticed a little pick up in the torque across all rpm range. Mpg seemed to gain almost 1mpg. But I also have 31x10.50 pro comp A/T on it with 3.55, I noticed an increase in mpg just getting the bigger tires, even with the added weight of new rear spring packs and lift parts. When I get my gas @ Moto it never varies, but QT gas seems to give a little extra. I use regular oils, have 12" subs in box, big amp, and junk in back all time. And, what type of tire you have makes differnece, IE...Mud terrain, Staright, what have you....