FYI FWIW YMMV: Stock MPG - one case study

I've been tracking mileage over the last four tankfuls. I've been running it down as far as I dare to minimize pump error, although that may be why the third tank appears to have done so well. OTOH, there was a time when I was purposefully lighter on the petal and kept the speedo down off of my usual 75 (I get in these moods occasionally).

I thought I would add a chart once in while as long as I keep up the records. The odometer was checked against interstate milemarkers over a 10 mile stretch. I recorded the odometer reading at each marker so I could catch mis-reads. The +5% actual over odometer is accurate, although I don't know if it's due to the 235 LT's or just OEM variance (probably a combo of both).

Anyway - Here's the first one.


I'm loosin' it - I forgot to sign it:

XJ Dreamin'
specs: like the chart says :wave:

What's really scary is, I do 1.5 tanks/week. YIKES!!

At 142k miles my 96 auto got 22 mpg on two tanks in a row f all highway driving. Speeds ranged from 55 to some 80 mph. Each fillup was about 300 miles.

JoBo

I have a stock 2001 Sport that my wife and I will be driving from Colorado to northern New York State in two weeks. I am hoping to average 22 mpg on the highway stretches. We're planning to cruise at 75 with the CC on to help smoothe the mileage. Think it's possible to average better than that on an 1800 mile highway trip? (On the back of a flatbed doesn't count!)

Lachlan

When I say "fairly heavy foot" I'm actually talking about a very heavy foot. I really think that the 19mpg from the third tank is the result of backing off slightly. But the damn Jeep is so much fun, I can't keep my foot out of it.

The mileage listed is probably about 50/50 city/highway, or maybe 60/40 in favor of city, and of course city is where mileage suffers the most: all that torque leaving each stop eats up the fuel. I have the choice of running the service road to work at 55mph or the interstate at (legally) 70mph. For my slow period, I ran the service road for at least 3 days, maybe 4. That's one tank of fuel, though I can't be sure that it was during that particular tankful.

Anyway, I'm back to the heavy foot and 75mph to work. I'm a little afraid to fix the beat-up motor mount that lets the exhaust rattle, or the spring wrap that vibrates the driveshaft because those are currently limiting the torque I can apply. I hope that openning up the intake and exhaust will magic up a couple of mpg, but I know I'm not going to be able to stay away from the extra torque.
XJ Dreamin'

Not quite stock, but close. 90 MJ 4.0, ax-15, 3.07's, 31's (4th gear only most of the time) 60 miles a day mostly cruising 70-80. Heavy foot. 20 mpg, on the tank I had it pegged 10 miles WOT in a headwind trying to go 80 in overdrive.

Well, I almost hit 20 with that third tankful, and that might be the time that I was going light on the throttle. When gas prices started going up in the '70's Dad made us drive 45mph to conserve fuel. It may be that I've been compensating for a deprived youth, but I am heavy on the throttle. My old Ram Charger only got 14.5mpg but that was a HP 360 w/ QuadraJet and I was very heavy-footed with it (it died at 350k*). So, I don't expect that I'll ever do much better than I am, now. I wanted to track it anyway so I can see if the upgrades have any effect.

I've also wondered if the ECM might be running rich. I know there are some fixes to lean it out but then it might just need a TB cleaning (yes, three years and I haven't cleaned the TB). Anyway, I'll cross 200k odometer miles with the current tankful, and that will kick off a year of upgrades, including: a 60mm TB, new intake, high-flow muffler, etc. Plus, I'll pick up some new sensors if any check out bad or marginal.

I'll add another column to the chart to log mods/upgrades. If I can swing a LSD or No-Slip I might go 4.10 but I don't want to get carried away. I'm saving real mods for this one's replacement in a few years. At my current rate, this one will hit 300k in four years. I hope to have a '97 select-trac built up by then, but if it takes 350 or 400k before that happens, that would be fine, too. We've got a 9yo and a 4yo so there's other stuff suckin' money right now - and for some time to come.

Keep on...
XJ Dreamin'

* Actually, it didn't die - I overhauled the engine and sold the rig (a long, sad story) and the buyer says it's doing quite well. "Realy scoots" were his words last I saw him. Oh well. But, I really love my XJ and it could give that Ram Charger a run for its money, stock! So it all worked out. GWIMW don't ya' know.

Re: FYI FWIW YMMV: Tank 6: 18 mpg

Apr. 29th.



No mods yet.

XJ Dreamin'

I've started putting my fuel log into the computer from the first fill up to the most recent, kinda curious to what kind of difference there has been since I got the truck. Good luck!

Last summer, 3500 mile round trip from WI to UT on I80 at 75mph, 21.8mpg, 01xj, aw4.

bjoehandley said:

I've started putting my fuel log into the computer from the first fill up to the most recent, kinda curious to what kind of difference there has been since I got the truck. Good luck!

Click to expand...

Now that it's hit 200,000 I plan repairs/upgrades over the next 12 months, including intake and exhaust, new tires, gears and lockers, sensor checks/replacements, etc. I started the log so that I could see if anything happens to the 18mpg average. When the mods start I'll note each in the log. There will be a few fill-ups between each mod, so it should be evident if any one mod makes a difference.

Thanks for the encouragement.
XJ Dreamin'

Sorry. That should be "..gears and locker.." - singular. It's only two wheel drive. I'm dreamin' again.

XJ Dreamin"

Did you add to the odo. reading for the +5%? If not then you all ready have over 200k, 209,862 to be exact. Just wondereng by the way.

scoobyxj said:

Did you add to the odo. reading for the +5%? If not then you all ready have over 200k, 209,862 to be exact. Just wondereng by the way.

Click to expand...

When I got the Jeep, at 130,010 miles, it had 205 or 215 P series radials. I immediately had the LT 235's from my Ram Charger mounted. I don't know whether the +5% is due to the 235's or just OE odometer error. If the +5% is only since the 235's then 200,000 indicated is actually 203,500 miles. If the 235's are not significant and the error is original, then, yes, +5% would be around 210,000 miles. In either case, it does not matter to the per tank calculations. I just increase each by 5%. I decided to wait for the odometer because that is the official count. The last tank might be at 18 mpg because I've been driving gingerly due to a leaking wheel cylinder.

Thanks for the interest.

XJ Dreamin'

1989, 4.0, AW4, 215/75/15, 3.55, bone stock, now 278K miles on odo. 2 years ago, measured mpg over 14K miles of driving about 40/60 city/highway, with lots of stop and go included. Close to one year worth of driving. Averaged 18.2 mpg.

Best mpg I have gotten was 26, all highway, at an average of 70 mph, on a trip to northern CA, when she was much younger!

FWIW ... Maz

Re: FYI FWIW YMMV: tank7

May 3, 2005

Tank 7


no mods

XJ Dreamin'

tank#8

suprise drop in average

Stock MPG: Tanks 9-12

Sorry for the late update



Fluctuations are still a bit of a mystery. There have been a few major flucuations in the MPG, but they have little influence on the average since they are isolated events, not trends. The overall trend is very steady. The red entry is an estimated mileage. I forgot to record the odometer although I do have the receipt so the Fuel entry is actual pump reading. I'm still thinking that most of the fluctuations are pump error although there is likely some driver attitude influences, depending on mood and how many jerks get in my way on a given day.

Stock MPG - tank 13

Left the gas cap off between fill-ups. It was on the hanger inside the gas door, but the filler tube was open the whole time between fill-ups. I doubt this would have much of an impact, but I though I'd make note of it.



mileage is steady. No mods yet but it's good to have a sizeable block of data before they start.

I've been keeping track of my mileage off and on and plotting it since I first got my 99 XJ back in 2000 with 23,000miles. So that's data for a 5 year period.
I now have 116,000miles on it.
The specs.
99XJ, Automatic, 4WD, Borla headers, Catback exhaust, synthetics in the front and rear differential and transfercase.
Tires over the last five years have varied between 215/75R15, 235/75R15, 225/75R15. I have a minor 1.5" lift.

I do a 60/40 to 70/30 highway/street mix of commuting.
The speed varies between 70 and 80 MPH on the freeway.

According to the linear trendline that I added to a plot on excel, the average is at about 16.5MPG. I haven't tried running an actual average.

The highest MPG I've been able to get is about 21 MPG.
Usually on highway driving I get around 18MPG.

What I have realized is that MPG decreases quite a bit at speeds over 70MPH even with cruise control. Air resistance certainly shows it's effects.
At 80MPH, on cruise control my MPG is in the mid 16s.

at 70MPH, on cruise control my MPG is in the 18-19MPG range.

I don't know how it is that you guys get mileage in the 20+MPG range. Maybe it's the California gas.
I regularly maintain my vehicle.

MAP