My Jeep 4.0L is getting unusually GOOD mpgs'....

[KDOG]

Hopefully it doesn't mean something is wrong. I'm just hoping its settling in. Its an '04 Grand Cherokee Laredo with the 4spd tranny and 3.55 diffs. Its got almost 130K on it. However I take great care of it. I religously change the oil every 4k with Mobil 1 full synthetic "High Mileage". Just had it tuned up not long ago (new plugs etc.). Theres a little trip/mileage computer on the overhead console that I reset when I'm at cruising on the highway to see what its capable of getting when I drive conservatively. Today it settled to the highest I've seen - held at 29.4mpgs. Usually thought it will show 24-25mpgs highway. Of course that average drops when I get off the highway, however even when I let it go to see what my avg mpgs are it stays around 21-22 - thats' combo city and highway. The engine feels smooth and nice. The thing just runs good but that highway mileage is SO good I'm wondering if there actually may be something wrong LOL. Am I just worrying too much? Did I just get a freak engine? Not that I'm complaining with gas prices going up. Any opinions?

 

[RavenSEAL]

Sounds like a trap!

 

[LTC8K6]

You need to do the fill up method.

MPG readouts are notoriously unreliable.

Why yours is suddenly way better is suspicious.

 

[Throckmorton]

I had a WJ and the mpg readout matched what I got by calculating myself.

Maybe it's malfunctioning though.

 

[SyndromeOCZ]

It got better for one trip down the highway? Which was was the wind blowing?

 

[herm0016]

tail wind? drafting? going 5mph slower?

 

[KDOG]

LOL. I've been seeing this for awhile now. I'll have to do the gauge measuring method to verify.

 

[EagleKeeper]

LOL. I've been seeing this for awhile now. I'll have to do the gauge measuring method to verify.

When you fill the tank; stop as soon as the sensor shut off happens.

Also, you may want to average the results over 5 tanks or so to account for weather.

Daughter has a 02 with 175K and she gets better mileage than my 09 when both are highway tested.

 

[richardycc]

29mpg? no way, my 06 Jeep with the 3.7L engine only gets 17mpg combined.

 

[JCH13]

If your old ignition equipment was garbage I'd believe a jump in fuel economy.