First off, if this has already been discussed a billion times, I'm sorry, but the search function on this forum doesn't work very well.
I have been seeing people mention that rotella oil is good for the XJ 4.0l engine because of the zinc. Which makes me curious what y'all use and why? Obviously there are going to be tons of different brands that work, I'm just curious what your options are.
Also, for oil weight, do you always use the weight recommended in the manual, or do you run a different weight and if so why?

 

Expect to get flamed relentlessly, because as you suggested this has been talked about ad nauseum.

That being said, I use 5w30 full synthetic. I live in an area where we have snow and freezing temps in the winter, and humid boiling temps in the summer.

My jeep has had 5w30 it's entire life, and I switched to synthetic around 50k (currently has 160k).

The 4.0 appreciates any oil, you can pretty much put any type/weight in it and it will thank you with hundreds of thousands of miles in return.

 

You are going to get a lot of answers to this , all I know when the 4.0 L was made they used 30w oil with zinc for the flat lifters now it hard to find that oil and it also cost more . I run a 10w-40 mobile 1 with a zinc additive , a lot of people use 15w-40 truck oil for the zinc .

 

Too much zinc is going to kill your catalytic converter - could be a problem if you have emissions testing where you live, especially if your XJ is 1996+.
5w30 to 10w40 depending on the temperatures that your XJ will see.
As jpz wrote above any decent oil that is regularly changed is all these engines need.

 

100% agree with changing the oil regularly. Honestly why people don't keep up with that is beyond me.
My Jeep is a '92 so I don't think I have to pass emissions in NC. I'd rather keep my engine healthy at the expense of my cat anyway.
I picked up a bottle of 15w-40 rotella but that's probably a little thick for winter here. I guess I'll look for a 5w-30 or 10w-40 rotella for my next oil change.
Maybe this is a dumb question, but would it hurt anything to mix different oil weights?

 

How many years did they have zinc in the oil and cars also had cats on them and the cats were doing ok . When I said I was using a zinc additive I'm using less then the recommended amount . And to hurt the cat you need to be burning oil to get the zinc to the cat .

 

I use Rotella T6 5w-40 with a Wix/NAPA Gold 51515 (extended length) filter.

 

I always mix my oil for my mid 90's Porsche for a little additional zinc and my Blackstone oil reports come back great. The recommended high zinc oil for the Porsche is 20W-50 V-Twin Mobil 1 for Harleys. In North Carolina I'd stick with the 10W unless maybe you live on top of a mountain and rarely leave. I personally think the 5W stuff is made for people who are well above the Mason Dixon line. I'm going to change my XJ oil this week and will be blending Valvoline VR-1 10W-30 Racing Oil (high zinc) with some as yet undetermined 5W-30 for NY, North East PA, and ski trips to VT/NH.

https://www.blackstone-labs.com/

 

Same oil but I run a Mopar Filter. Can get both from the local walmart.

 

MY jeep definitely burns oil, so I guess my cat is screwed lol

 

 

Jeep Engine Oil Viscosity

This was taken from pages 82 and 83 of the 1989 Chrysler/Jeep owners manual.

Selecting Engine Oil Viscosity

When changing or adding engine oil select the proper grade by using the chart on the following page. Select the grade that corresponds to the ambient temperature range you expect to encounter before your next oil change.

30*F to 100*F+ 20W-40 or 20W-50
0*F to 100*F+ 10W-30 or 10W-40
-20*F to 60*F 5W-30

 

Whatever weight your owner's manual says.
Full synthetic.
If the maker of a brand has a High Mileage version full synthetic, check and see if your mileage fits, and use it.

 

Some counties in NC don't have emissions testing. The counties that do have emissions testing in NC follow this rule. If your vehicle is more than 20 years old, it doesn't have to be emissions tested.

For all of NC, if your vehicle is more than 30 years old, you don't have to do a safety inspection either, so that means no inspections at all.

 

Rotella 15-40 is great for nearly all climates!! 0 to 100!!