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Old 07-29-2010, 01:35 PM   #14 (permalink)
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comptiger5000's Avatar
Join Date: Feb 2010
Location: CT, USA
Posts: 544

RaceJeep - '98 Jeep Grand Cherokee (ZJ) 5.9 Limited
90 day: 13.62 mpg (US)
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Yeah, this thing has a bit more engine than it needs. And, it probably burns about 1gph at idle . Then again, the 4.0 I6 isn't much better for mpg either.

The 6.8 second 0-60 is great for merging onto the highway though, when you get stuck behind the idiot doing 25 up the on-ramp and not accelerating to merge into 60 mph traffic (happens a lot around here). Just punch it, merge and settle into a nice, slow cruise in the right lane. Plus, getting on from the stop sign ramps on the Merritt (or other short ramps), it's priceless to see the face on the guy in the BMW behind you when you punch it to get on in heavy traffic and tear away in a blast of V8 noise leaving him thinking "wasn't that a Jeep?"

Plus, the 5.9 Limited is a fairly rare special edition, of which only 14,286 were sold in America (not sure if the total includes US and Canada or just US). With the bigger engine and extra power came a slightly nicer interior, slightly different exterior, electric cooling fan, heat extractor vents in the hood, better exhaust system (most people don't believe it's stock when they hear it), the need for premium gas, and only very slightly worse gas mileage than the standard V8.

I'll agree with it having lots of aero drag. It's not terrible weight-wise compared to a lot of SUVs, it weighs about 4200 pounds. Certainly not light, however. Rolling resistance is actually pretty low. Especially if I neutral coast, but even in gear if not in DFCO, I usually gain more speed than most other vehicles down hills, even doing 60 or so on the highway with all the aero drag.

I plan to try to clean up the underbody airflow a bit, and maybe eventually do a removable kammback for long trips. More aggressive use of TC lockup should help out a good bit with the transmission inefficiency.

I can also help the engine efficiency a bit with small things like upgraded fuel injectors with a better spray pattern than the crappy stock ones, giving a better burn. All told, I hope to get it up to 15mpg around town and 25 on the highway (maybe with slightly taller gears).

Fortunately, once I leave for college in a month, it will no longer be subjected to the daily commute in city traffic, etc. and I should be getting much better mpg. My normal around town grind is terrible for mpg. Plus, once I replace the plenum gasket this weekend, I should get a little better mpg. Maybe I'll get to about 13 around town. I just try to stay positive and compare my mpg to the EPA ratings (11/16). I would actually have to try, especially on the highway, to get mileage that bad (I can break 19 averaging 65mph with the A/C blasted). I expect to get about 20 - 22 on my trip to college (350 miles). As long as I get at least 20, I'll be happy, as I'll be able to do it on 1 tank of gas without sucking it dry (23 gallon tank).

After college I plan to buy something more efficient and retire this thing from DD duty. However, for now, I need the cargo capacity, possibly the towing capacity, and the deep snow capability. And on the highway, all the low end torque makes it very pleasant to drive. It's not screaming along (turns about 1800 at 60mph). Plus, once it's in OD with the TC locked, unless I have to drop below 40 (or about 45 on the steepest of hills), it never downshifts.
Call me crazy, but I actually try for mpg with this Jeep:

Typical driving: Back in Rochester for school, driving is 60 - 70% city

Last edited by comptiger5000; 07-29-2010 at 01:46 PM..
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