Gas mileage

[yjcanibul]

03 tj 4.0L 5spd    epa says stocker = "  15/17mpg city/highway  "


89 yj 4.2L 5spd    eps says stocker = " 15/18mpg  city/highway "   
                                                     actual= modified , 33" tires +100hp I am about 14 mpg city

check yours at

http://www.fueleconomy.gov/FEG/bymake/bymanuNF.shtml

[Vinman]

I went to larger tires and compensated for the difference in odometer and speedometer readings using GPS etc.  Having done that, I can say it felt like I was accelerating more slowly even though I wasn't, but since I didn't change gearing, I also had to work the engine harder to get the same "feel" of acceleration.  Like I said above, I actually was accelerating pretty much the same, but the lack of engine revving made it seem to me that I was accelerating more slowly. Watching the actual speed etc. showed that it was about the same.

Since putting on the new tires, I got a ScanGauge II and used it to adjust my driving (which annoys the cr*p out of impatient drivers) and I'm now getting about 25% better mileage than I did with the factory tires.  For example, I now get about 500KM out of a tank instead of 400KM. I accelerate more slowly, but seem to catch up to the group once I'm up to the speed limit, never mind at the next red light! It's a lot less wear and tear on the entire drivetrain, including brakes, clutch, tires etc. due to the more smooth driving. I drive more by throttle opening than speed, so my speed does drop off on hills, though I don't let it get crazy and drop a gear to stay "close" to the speed I was doing.

I also concur that with speeds over about 70KPH, the drag increases considerably based upon the required throttle opening to maintain a given speed.  80KPH is pretty much the best compromise, though I usually do 90KPH with decent results.  Once I go to over 90KPH, the mileage drops off  significantly.  Numbers?  Well, on the highway at 80KPH on fairly flat terrain, I can get under 11L/100KM and sometimes can get that in the city too. My "typical" is high 12's and low 13's on anything but a short hop.

The caveat is that I didn't have the ScanGauge with the factory tire size and so didn't have the benefit of the driving changes for a fair comparison.

The subject of throttle opening versus gearing versus RPM etc. is a pretty complex subject, hence why engine computer programming is an arcane "art"   Sure, it's easy to say that "everything else equal", the less RPM, the less fuel used, however it's that "everything else equal" that gets you.  If there is a corresponding increase in load due to the lower RPM (higher selected gear or bigger tires or lower numerical gearing), then chances are the computer is enriching the air/fuel ratio, so for a given RPM, more fuel is used.  It's a trade-off and without the ability to reasonably accurately measure things in real-time, it's very tough to determine what works best.  Oh yes, I did discover that when my mileage was dismal one day, that my tire had also dropped to 8Lbs or less for some reason.  The basics apply, maintaining engine tune (air filter, clean engine, spark plugs, wires etc.), slick lubricants, regular chassis lubrication and maintenance, optimal tire pressures, minimize stuff causing drag, smooth driving etc.

Egads... enough rambling..   While I don't buy a Jeep for good mileage, that doesn't mean I don't want to get the best mileage out of it that I can while still having fun!

I can tell you a couple of things I noticed with my 3 Jeeps that Ive owned over the years.

First was a brand new 96 Cherokee XJ with 4.0L and 5 speed tranny.
Stock and with 30"AT's the mileage was incredible. 74 liter tank would give me at least 650 km's (city driving) on a regular basis but the all-time best was on a trip from BC, I filled up in Nanaimo BC, drove about 95 km/h with fuel mileage in mind  and when I got to Golden (748 kms!) I still had a 1/4 tank left. That trip was over 30 mpg!!!

Second was with a 2000 TJ (4.0L 5 spd) on 31"AT's. The usual mileage was 24-25 mpg. On one trip from Vancouver through highway #3, I used 4th gear all the way and mileage did not change one bit compared to 5th gear.

The last was 2003 Rubicon (4.0L auto). The absolute best mileage I got was about 20-21 mpg and that was with 35" MTR's and 5.13 gears. The gear change from 4.10's to 5.13's actually increased the mileage by about 10%. The mileage was calculated with GPS and the speedo was actually within .5 km/h thanks to an electronic calibration unit. With that Jeep the mileage didn't really change if you drove it 80 km/h or 120.

Vince

[Tinkerer]

I can tell you a couple of things I noticed with my 3 Jeeps that Ive owned over the years.

First was a brand new 96 Cherokee XJ with 4.0L and 5 speed tranny.
Stock and with 30"AT's the mileage was incredible. 74 liter tank would give me at least 650 km's (city driving) on a regular basis but the all-time best was on a trip from BC, I filled up in Nanaimo BC, drove about 95 km/h with fuel mileage in mind  and when I got to Golden (748 kms!) I still had a 1/4 tank left. That trip was over 30 mpg!!!

Second was with a 2000 TJ (4.0L 5 spd) on 31"AT's. The usual mileage was 24-25 mpg. On one trip from Vancouver through highway #3, I used 4th gear all the way and mileage did not change one bit compared to 5th gear.

The last was 2003 Rubicon (4.0L auto). The absolute best mileage I got was about 20-21 mpg and that was with 35" MTR's and 5.13 gears. The gear change from 4.10's to 5.13's actually increased the mileage by about 10%. The mileage was calculated with GPS and the speedo was actually within .5 km/h thanks to an electronic calibration unit. With that Jeep the mileage didn't really change if you drove it 80 km/h or 120.

Vince

Are those calculated with Imperial or US gallons?   I'm curious... then I'll post some of what I'm getting with my tire sizes etc.

[yjcanibul]

they would be U.S. gallons , just assume it all evens out letting it warm up 100 times during winter then pushing a ice cube down the road ... else since cdn gallon is .7 ltr bigger assume our epa mileage should be about +2 miles better per gallon ...

from what I understand,  the epa ratings are seldom reached in the real world of hills, winter, traffic jams ... exceeding those numbers is awesome  !

[Vinman]

Are those calculated with Imperial or US gallons?   I'm curious... then I'll post some of what I'm getting with my tire sizes etc.

Imperial gallons

[Tinkerer]

While I'm "in there" on city mileage, somewhere from 11.0 L/100KM (25.7 MPG Imp 21.4US) all the way up to 13.0 L/100KM (21.7MPG Imp 18.1US) depending on trip length, hills, traffic etc., but more typically in the high 11's and low 12's.   Deerfoot to Okotoks, I can get down to low 10's (~27MPG Imp 23US).   That's well above what even the adjusted EPA numbers state even when adjusted for US gallons.

I'm running approximately 31's (LT285 75 R 16) with a 1.5" lift and everything else pretty well stock on the '04 Rubicon, though now I'm thinking I might benefit from checking all the points of maintenance due up to 65,000KM.

[yjcanibul]

thats decent !   I didnt realize anyone was seeing +20 mpg

my speedo is out ,  if I dont consider that I get 18mpg city, 
might calc it that way for awhile so I feel better ...

driving I tend to use a lower gear than perhaps is required, 
like going up crowchild I use 4th at 80km at 2000rpm, if I
drop to 5th it goes to 1500rpm - its not a slug but it looses its
zip which I like ... maybe will try and go econmise this tank
and see if makes a diff at the pump ...

btw:  rumor is std trannys will be offered less in the near future
due to auto's being computer controllable and avoid what I desc
as my driving habit above ...

[Katt]

I've noticed that down shifting for hills is the only way to go. If I avoid 5th altogether, that check engine light comes on (nothing a peice of electrical tape on the dash doesn't fix ). I wasn't thinking fuel economy when I bought it. I was thinking JEEP.
Also, I would NEVER put an oilers fag -I mean flag- on my JEEP. Such a subject isn't worth bringing up. We all know the truth...