I noticed about 1 or 1.5mpg gain without the racks. I don't use em, and since my xj is getting 14/18 mpg i need every bit.

 

probably best advice, haha

still, i'd like to get the best possible MPG out of my 98 auto XJ..... im no expert, just a bit of an over analyzer, & extremely curious.... the info is out there, it's been thought of, asked, tested, & results shared....SEARCH ....good info i've found regarding better MPG's include a few basic principles ....mass (weight), temperature, volume & flow

the less mass (weight), the better.... so obviously MPG decrease with larger tires, axles, heavy bumpers, roof racks, etc., add weight.... not only because of the weight, but the wind drag thats created at highway speeds.... already driving a vehicle as aerodynamic as a box, plus lifting it, there's not many ways to avoid this drag, other than building/buying lightweight components (aluminum rims, bumpers, etc), & installing wind directing skids.... in addition, the force needed to rotate mass, also drags down.... removing mechanical clutch fan (& replacing with electric) minimally improves

lower temps the better for intake tube, manifold, & overall ambient engine compartment.... a true COLD air intake (cowl, snorkel, etc.) is best.... optimize by insulating the intake tube & manifold (proper insulating material to keep warm temps from absorbing).... manifold sits directly above exhaust, so imagine how much heat the intake air absorbs.... hood vents are functional....proper placement is key too..... many factors come into play, & obviously the xj isnt all that aerodynamic, but wind passing thru & over the bumper/header, & over the hood & windshield creates wind pressure areas that, in conjunction with properly placed vents, can pull cool air in & expel warm air

more air coming in (following allowable engine CFM parameters) to mix with fuel & combust, & the appropriate air exhausting is are other upgrades.... starting at the manifold, install 99+ intake manifolds that have better flowing plenums, install larger bored throttle body, install upgraded injectors (1-hole, to 4-hole spray), install better flowing exhaust headers, & high-flow cat & muffler

info i'm still looking up is regarding combustion.... higher output coil, distributor, larger wires, & best spark plugs..... everyone has their own debate.... some say upgrading coil & distributor doesnt make a difference, others say yes, some say E3 spark plugs are garbage for the I6 4.0, yet some argue they've seen improvements

SO, yea, cheaper to buy a little 4 banger beater so save some $$ at the pumps.... but there are things that can be done to see not only power gains, but improvement in efficiency, resulting in better MPG's

& again... SEARCH, then, SEARCH some more

 

Best gas mileage dont drive it and get a horse or get a moped But also it helps if you run like 33s to take them off for regular driving for stock size tires

 

Well I drive a 93 geo metro xfi 5 speed. I drive it to work and back. And around town.45 mpgs..then 17 with the XJ.

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I'm a delivery driver for Jimmy Johns and i usually use a on my deliveries. It is awesome. I have only really done the math once, and for that tank I got around 60-70 mpg on it. It takes me less than $4 to fill the tank from bone dry...and gas is $4 and some change around here.

 

When I have to use the XJ on deliveries I just want to cry.

 

Dang. I'd like to get a scooter. I'll need to look into one. That's awesome gas mileage.

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You could always be on the frontier of XJ technology and try a hydrogen fuel cell. It's definitely on my list before the end of the year.

http://mileageshop.com/mileage-saver-complete-kit

 

if i had $300 lying around id totally buy that to try it. iv been hearing about hydrogen powered engines for a few years now so its very appealing to me. anybody here have/know anyone that has one?

 

x2!!! This looks very interesting. I would like to know how it ties in to your engine and if it actually works. If anyone has this please comment!

 

gaseous hydrogen and oxygen are highly flammable, and definitely have fuel potential. Granted that it has a long way to go before being a stand-alone fuel source, but you can get a good boost in MPG super cheap. I made a crude version of the HHO fuel cell a few years ago out of a gallon jug, water, lye, and aluminum cans. It produced a wicked sustained flame, but the jug blew up b/c I used too much aluminum/lye.

The kit that was linked has no chance of that happening b/c it uses electricity to split the water...and it's pretty easy to install. If you can install a set of offroad lights with a relay, you can install the kit. The gas feeds straight into the intake tube, so there's nothing mechanical, electrical, or electronic to modify. It hooks up kind of like a cheap nitrous set up...

It'll take me a month or two to pay off my other XJ parts, but I'm definitely getting one then. I'd happily be the forum guinea pig on this one...

 

That'd be awesome if you could. Haha a 30 mpg lifted xj.. That'd be freakin cool!

 

Heres a short list:
Lighter oil in synthetic, will help MPG.
Do a tuneup with new plugs, cap, rotor and wires, make sure the timing is close to spec.
Make sure your tires are aired up to spec.
The number one thing that will increase MPG is YOU.
Slow down and enjoy the scenery and learn to like 55mph or so, this will be the biggest increase in MPG.
After All we drive a vehicle with the aerodynamics of BRICK, and then add a lift kit, so not its got the Aerodynamics of a BRICK sitting on a 4" 2x4.

 

But it's no fun if you don't drive it like you stole it...

 

Oh this is so true but keep in mind the ones who are enjoying the $#i! out of their jeeps aren't the ones begging for mileage either my daily driver gets 14.2 MPG and I drive about 115 miles a day round trip... why in the h#!! would I look for my toy to get any better than it...