Gas Milage 4.0L I6...13.5 mpg?!?

I just went through my first tank of gas with my recently purchased 2000 Grand Cherokee Limited (4.0L I6).

I only got 13.5 mpg (in town)... I was definitely expecting better than that with the 6 cylinder... does this sound right to everyone else?

If it was all stop and go or with a heavy foot, that might be right.

I'd take it out on a highway drive, see how it does.

our 97 JGC I-6 gets around 15-16mpg with a mix of highway and city driving. before gas companies switched to the winter formulas, it got 17-18mpg.

Just averaged 19 mpg on a 700 mile road trip in my 2000 4.0. Mostly highway at 70+ mph.

I have a '94 Geep GC and just got about 12.5 MPG on a tank. The next tank was 13.5 (all city driving, or pulling a trailer). When it was new I drove mostly highway, and topped out around 19 MPG. I don't know if it would do that today, even on the highway.

a common issue with the 4.0l Jeeps getting bad gas mileage is the oxygen sensors. It's a common topic at jeepforum[dot]com.

The upward o2 sensor (closest to the motor) can slowly die and not set off a CE light. Replacing it takes a matter of minutes if you have a oxygen sensor socket (can be rented at Autozone).

The obd1 rigs don't seem to mind what sensor is used (I used a Bosch one purchased from autozone on my 94 and noticed a difference for the better as far as mileage is concerned). The obd2 rigs seem to be a bit nit picky and dealer o2 sensors (mopar) are recommended.

The upward is the one that needs to be replaced (atleast in my case, obd1). The downward (after the cat) o2 sensor is basically there for comparative purposes, but doesn't seem to affect the computer (and your gas mileage much if at all.)

hopefully that was some help :)

I think that is what is wrong with mine, because my gas mileage has been slowly decreasing over the past few weeks. How much is an oxygen sensor, approxmatley. Thanks.

i just purchased a 2001 jeep GC i6, i went through a tank and a half and im getting an average of 18.8. 60% town, 40% highway driving.

FYI- on a 140 mi highway trip last night the Jeep (13.5mpg in town) got 21.5 mpg! Guess there's a pretty big difference between getting the thing rolling over and over again, and just cruising at 75 mph.

There you go..... I average about 17 going to work and back, but it's about 60% highway. I got 19mpg on a highway trip a couple weeks ago, mostly at 75-80mph.

oxygen sensors for these are around 60-80 dollars for the Bosch ones for the OBD1 rigs.

The Mopar for the OBD2 are pricey from the dealership, try and find them else where on the internet if you can :)


between getting the thing rolling over and over again, and just cruising at 75 mph.
That's awesome mileage, especially for going 75.

Another thing to make sure of on any car if you're getting less then desireable gas mileage is your tire pressure :)