salad

lol Easy now, dude! I said there was probably an issue! I never said this was 100% accurate and I apologize if something I wrote made it seem like that. I DID say that I just used the trip odometer, which I expect that probably is off but I don't know how much and I also assume that most other people are just going off of that as well, as in a stock configuration it will be 'close enough', as opposed to larger tires with different gears, etc. I'm just trying to demonstrate that decent fuel economy is possible in a stock configuration if you keep your speed down... If you'd like me to present ALL of the data I have I suppose I could, these are just a couple of samples from my spreadsheet of the last few months.

And for that last measurement I was off more than I thought - put 15 KM of additional city driving in and topped up again, put in an extra 5.852L, bringing the second half with faster speeds and the tires in the back to just over 23 MPG.

Anyway this isn't totally related so I apologize to the OP. I guess all you can gain from my posts is that speed, acceleration, time spent idling, and weight have a tremendous effect on economy in these things.

macgyver35

Hmm...

I'm not accusing anyone of presenting false information, but getting nearly 27 MPG is a bit tough for me to believe.

I have a '98 with a freshly remanufactured ATK engine in it that has about 7000 miles on it right now, so it's not still "tight". Every sensor was replaced at the time of the engine swap. New plugs, rotor, coil, filters, on and on and on... It purrs like a kitten. It also has Neon injectors and all new exhaust system. All new cooling system. Trans works great and had a full fluid flush 2 months ago.

I have a 2" lift, 3.55 gears, and new Firestone Destination 235/75-15s. Stock body, no heavy bumpers, etc.

Last weekend I made two trips from Arlington to Kaufman, which is 98% highway and a very flat run, no A/C, and had the cruise set at 68. About 220 miles of driving. Not any wind to speak of. I got 20.7 MPG that weekend.

I would say that since dang near everything under my hood is new, or newly rebuilt, I'd have as good or better chance as anyone of getting good mileage. But it's just not there, and I'm not sure what kind of magical change I could make that would net a 25% increase over what I'm getting to fall in line with the nearly 27 MPG claim of the OP.
Again, just a bit hard to believe.

Only thing I can think of is that the air is less dense at higher altitudes, but I don't know how much of an effect that would have. In my part of Texas, we're only about 600 feet above sea level...

nv6r

I am a mechanical and electrical engineer, so I think I know how to measure MPG. Plus, I also know a thing or two about aerodynamics and engine design.

nv6r

IDK, I have managed to get better than 25mpg from 2 different XJs, both with the 4.0l -- actually, I have had a couple with the 2.5l and they actually got worse gas mileage. My current XJ will manage 23mpg on a very good day (more like 18), but has seen a max of 30.16mpg before I did the lift, winch, and bumper. I am running a unique combination, however, that was purposely engineered for better TQ, which will automatically increase MPGs; so, no, I am not stock: I am running 3.55:1 gears (instead of 3.07:1), an AX-15, full-sized header, and the Neon injectors.

With this combination, the TQ peak is much lower (2400rpms instead of 3200rpms; and much flatter than stock: within 15lb/ft from 1800-3500rpms), and throttle response is much better, too. Because of the TQ peak and curve, gearing, and injectors, I rarely have to downshift out of 5th when climbing moderate hills, which is conducive to better gas mileage; keeping any engine close to the TQ peak is what produces best MPG, and the flatter the TQ curve, then the more wiggle room you have to work with. I am also designing a solid lifter cam to try to increase the low-end TQ even more. The problem with the XJ, is with it's injection and computer system, you have to use a cam within a specific lobe center angle and intake centerline, or it won't run right.

hankthetank

You can't measure mpg on one or two trips! Seriously! You need to go through like 10 tanks of fuel to get an average that means anything. I could probably get 20- 25 in my lifted pos renix on a highway trip, but that doesn't mean jack ****! Does anybody agree with this?

salad

Okay, that's fair. I noticed an error on my spreadsheet regarding my last post so here's what I have for pure highway driving, measured via liters dispensed at the gas pump and the trip odometer of a stock XJ:

28.623 (March, flat terrain avg 110 KM/H, some drafting)
27.577 (last week, hilly, average 80 KM/H)
26.990 (yesterday, hilly, picked up some tires on the way back, average 90 KM/H)

Combined highway/city:

21.108 (December, full load of humans and Christmas stuff, flat terrain 110 KM/H and a day of shopping)
19.252 (January, hilly, average 85 KM/H plus several days in town)
17.606 (March, flat terrain avg 110 KM/H, almost 2 weeks of in the city, just adding "some gas" before i topped off because I kept missing cheap night)
22.059 (March, same trip as the 28.623 above but bumming around with my friend over the weekend)
20.038 (last week, hilly, average 80 KM/H plus several days in town)

City:

14.320 (Jan)
13.215 (Jan)
13.535 (Feb)
13.384 (Feb)
14.620 (Feb)
14.861 (Mar)
14.756 (Apr)
16.908 (Apr)
14.979 (Apr)
16.499 (Apr)
14.789 (May)
15.604 (May)
14.815 (May)

hankthetank

Or, 17.9 mpg...to put it simply.

Marcucco

My 89 Pioneer (bone stock 2WD) would consistently get 25 mpg on the highway @ 60-70 mph
(I used to drive from RI to WV twice a month so that made it easy to track accurately)
But that was pre-ethenol.

The 96 2 door XJ (also stock, 4WD) got 20-22 on a 60 mile, mostly highway commute this winter.
(but it dropped like a stone on the days the traffic crept along bumper to bumper)
I plan on adding some of the intake and exhaust upgrades so I've been keeping track.

Both vehicles had 5 speeds, stock size street tires, and were well maintained.
Neither had any power options (windows, seats, etc) so they were comparatively lighter weight.
I think this makes a big difference.

If you're really worried about mileage, dump the bumpers, winches, roof racks, monster tires, and take out the lift kit.
...or find a **** box DD with a 4 banger.

salad

Where do you get 17.9?

ManiacXJ

That is the average of all the mileage numbers you posted.

salad

Why would one average highway and city mileage together to obtain average highway mileage? Nobody has ever made any claims that these things are good on gas putting aroud town. I've only ever been talking about highway econony, which I believe everyone in this thread clearly stated from the start.

hankthetank

... yeah you're right we've totally jacked this thread. He just wanted ideas for improvements in economy for highway hyper miling...

unsubscribed.

Devodale

HAHA!!!! 400 miles to the tankful! Yes, I drove it on "E" for the last 15 miles, but I wanted to make it to get this pic! This, from a completely stock 99 XJ with 257K on it. My secret was to go the speed limit......or less.

Cherokeekid4x4

I'm lucky to get 250 to the tank... you sir are lucky!

PNWjeeper

X2 on that and at $70+ per fill up is a real kick in the....wallet