Just bought a 1995 Grand Cherokee w/ 160K miles on a 4.0L 6 CYL. It's been on dino oil for all of it's life; I've synthetics in all of my other stuff from nose to tail. Should I stay with dino oil in this engine, or may I safely convert to a full synthetic?

This is south Alabama; mild winters of rarely less than 25F ever, but summers hover over 95F for several weeks.

 

Here are some motor oil facts......opinions will soon follow.

http://www.supramania.com/aehaas/

 

This question opens more cans of worms more than any other. Run what you want with a quality filter from WIX, Mopar, or anything other than FRAM.

 

If you want to run a synthetic, do it. No harm will come.

 

My Opinion.
Run a quality filter. Run a name brand oil. No bargains in the basement of this issue.
The Peep runs daily, 585000+km on the clock. I run Quaker State 10W30 and change every 5 - 7000 km. The QS holds pressure best (tried many name brands) for me thru to the end of cycle (still 52psi when hot after 7000 km).
Synthetic is absolutely excellent. I use RoyalPurple in my 350SBC Thundercar, 6400 rpm at end of straight every lap. I change it everyother weekend. I don't need that degree of protection (and cost) on my 4.0 which shifts under 3000 and generally runs for miles and miles at 1500 - 1800 rpm.
If you ride your XJ hard and put her away wet, then go synthetic.
Check out that attachement earlier in the thread and save it. Great oil comparisons and facts in there.

 

Rotella 15w40 and a mopar filter.

 

I use

 

I don't have a problem "investing" in synthetic; but I was told by a local mechanic that synthetics can SOMETIMES clean stuff off too much and that it can leak where a dino will not...?

 

Motors leak because of bad gaskets/seals.

 

Thanks, Fellas. Substantial replies and I'm looking forward to this "project". I can fly the hair of $11 million Army BlackHawks, but this is new ground, sorta. --Bryant

 

First off I would like to thank you for your service.

My personal preference is Rotella 15-40 in summer and Rotella T-6 5-40 for winter for easy starts. Now I know you don't get as cold where you are at as up here so I personally would go 15-40 with a Wix 51515 filter, its the oversized filter that I run on my big block mopars but they are the exact same mounting face size but they hold more oil and have more filtering.

 

Rotella is a very common oil around here. The link djb383 posted is an excellent read. I can't remember if it discusses the additive package or not, but the reason Rotella is so popular is the high ZDDP content. The Jeep 4.0 has design roots in the 60s and by the time it was retired in 2006 it was pretty much on life support. The engine has old stye flat tappet cams which wear very fast with modern AP SM oils or whatever is current as they have very very little zinc. Using Rotella is like switching to a "high mileage" oil and actually paying less: The pails of 15W40 conventional can go on sale for reeaaally cheap at some farm supply places, and a jug of T6 5W40 is priced regularly lower than all of the Mobil1 oil. A lot of the 4.0s can take the #W40 oil just fine, however there is a 10w30 Rotella as well.

Anyway whatever you dump in the crank case just don't put a FRAM on it