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Old 08-11-2010, 09:57 AM   #14 (permalink)
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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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I don't do a ton of long highway trips, so I don't know if hills do better than flat ground in the beast, but I'm pretty sure they're not worse.

However, compared to the 4.0 I6, I get the same or better mpg on the hills, although it can beat me by 1 or 2 on the flats due to the displacement difference. It definitely helps to be able to pull at a hill at 50 in top gear turning 1500, or even 60 turning 1800, while the 4.0 would have to downshift a gear at any speed on most hills, meaning it would be turning 2100 at 50, or a bit over 2500 at 60. In these not-so-efficient old school engines, the extra RPM loses to the extra displacement.
Call me crazy, but I actually try for mpg with this Jeep:

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