is it under warranty, if so, change it when the owner's manual says to do it, otherwise you risk voiding your warranty.
From the manual:
NOTE: Under no circumstances should oil change
intervals exceed 8,000 miles (13 000 km) or six months,
whichever occurs first.
8,000 Miles (13,000 km) or
6 Months Maintenance Service
❏ Change the engine oil and engine oil
❏ Rotate the tires, rotate at the first sign of
irregular wear, even if it occurs before
8,000 miles (13 000 km).
Synthetic Engine Oils
You may use synthetic engine oils provided the recommended
oil quality requirements are met, and the recommended
maintenance intervals for oil and filter changes
Jeep manual says change at around 8k miles, I got a free service agreement where they change it for free every 3k, so that's what I'm doing.
1989 Cherokee Pioneer
http://goo.gl/OspLWH - amazon link