Topic: Gas Mileage Thread

[mrcabinet]

2001 TJ, Hardtop, 2.5, 5 spd., 4.56 gears, 33x12.50 BFG ATs.
4" lift, Flowmaster exhaust, Airaid intake, 62mm TB & spacer.

Combined mileage before the TB/Spacer was 13.9. After, it went to 15.3.
I'm pleased, since I have more power along with better gas mileage. Hopefully
when I do an e-fan this spring it will improve a little more.

[hotwired]

 Around 14MPG with stock 97 TJ 2.5L, 4:88's and 35" MTR's, speedo is re-calibrated.

[Lu]

2.5L, Ax-5, Stock gearing, 31's, hard top, 4.0L TB, spacer, airaid CAI, royal purple oil, magnaflow exhaust, accel coil powering bosch platinum +4 plugs, small shackle lift, recent tune-up,

between 16 and 18 mpg

[Jeffy]

Just wanted to update.  With the Con-Ferr rack on top the Jeep's mileage dropped 1.4MPG as expected.  Still averaging 15MPG with mixed driving otherwise.

[firebrick43]

When I bought the Jeep I was getting 18mpg

I am now getting 23MPG in mixed driving(20 miles of 55mph two lane hiway normally at 60mph, and 10 miles of city stop and go at ~30 mph)

I have a 91 2.5 with every thing now working correctly. Replacing several vacuum lines that were leaking(especially the one the fuel pressure regulator, and fixing an exhaust manifold leak saw me get to 20MPG.   Mobile 1 in the engine but have not put synthetics in the tranny/rear ends.  Using a 4.0 TB and boring out the intake manifold Saw a significant gain in power and a 1-2 mpg increase in fuel economy. 

I am running 235/75R15 Michiline's LTX with stock gearing which is a 29" tire if I recall correctly, this got me 1mpg to 23. 

[jfrabat]

Jesus, it seems that everyone's mpg's keep going UP and mine keep going DOWN!  I guess I'mm adding all the wrong parts for mpg...  BUT, then again the Jeep is no t a daily driver, so I ratehr go for power than mpg now.  Still, I know there is room to improve, as I can still smell a faint gasoline smell when I fill up the tank, so I'm sure there is a small leak SOMEWHERE above the tank (already tried twice to lower it and fix it, but no luck so far!  At least it's a very FAINT SMELL, and no liquid is seen spilling; it's only fumes coming out if you ask me, and you can only smell it if I park the Jeep in the garage and stick your nose in the fenderwell behind the DS rear wheel.)

[chardrc]

ive also noticed that my my front driveshaft is totaly free in 2wd. when a customer had me look at there 01 tj the front driveshaft and axles were always engaged even in 2wd except the transfer case isnt lock'd.

that's what the vacuum disconnect on the passenger side of the front axle is for. supposed to increase mpg by having less rotating stuff, but they eventually found it cost more than they thought it was worth and stopped having the disconnects when they made the TJ.

[Jeffy]

Jesus, it seems that everyone's mpg's keep going UP and mine keep going DOWN!  I guess I'mm adding all the wrong parts for mpg...  BUT, then again the Jeep is no t a daily driver, so I ratehr go for power than mpg now.  Still, I know there is room to improve, as I can still smell a faint gasoline smell when I fill up the tank, so I'm sure there is a small leak SOMEWHERE above the tank (already tried twice to lower it and fix it, but no luck so far!  At least it's a very FAINT SMELL, and no liquid is seen spilling; it's only fumes coming out if you ask me, and you can only smell it if I park the Jeep in the garage and stick your nose in the fenderwell behind the DS rear wheel.)

Drive slower and your mileage will increase.  55mph is a pretty good compromise for mileage v. speed.  Go faster and the mileage will take a quick dive.

If you can smell it in the fender well then it's probably the 90* rubber tube on the fuel filter.

[jfrabat]

If you can smell it in the fender well then it's probably the 90* rubber tube on the fuel filter.

It's actually the rollover valves; i can see where it leaks a bit, but I cannot get them to stop leaking.  Next time I drop the tank, I may end up using some RTV there...

[firebrick43]

Most RTV is not fuel resistant.  The make potting compounds and non hardening sealers for fuel systems. 

[Jeffy]

Buy new breather line and replace them completely.    Otherwise, cut and re insert.

[jfrabat]

Buy new breather line and replace them completely.    Otherwise, cut and re insert.

That's what I did the last time, but it seems the gromet for the plastic valve is the one leaking...

[FourbangerYJ]

Last trip out was just a tad over 13 MPG. This will drop to about 11 when I take the soft top off. Seems the adjustable FPR has not changed my mileage.

[Jeffy]

tires make a big difference on fuel mileage. My non winter tires are toyo open country's. winter tires are firestone winterforces. with the winter force i was down to only 16mpg city or highway. also I run 5w-30 motor oil. lighter engine oil can slightly improve fuel mileage as well. 5w-30 is all i ever ran. using a 10-30 or 10-40 i wouldn't actually know how much of a difference it would make fuel mileage wise. but once i poured a whole bottle of STP in my subaru and that really slow'd the engine down. least it toke care of a bad valve tap in that motor til i sold  it.

Also, some states change the blend of their fuel so you end up getting less mileage as well.

All I run is mobile 1 5w30.

[aka-justin]

Update:

After replacing my TPS sensor and accounting for the difference in mileage for a 31" tire, my last tank of gas with mainly city to small amounts of highway, easy driving was 15.7 MPG!!!  Much better than my inital 10-12 I was receiving before recalculating for difference in tire size and bad TPS unit.