You would need to review the manufacturers data sheet to confirm the base oil composition. Either way, there is nothing to fear with any of the high mileage offerings in that grade. The Pennzoil/Quaker State offerings are good as is Valvoline High Mileage Maxlife. Winter is coming to an end, but depending on where you live, a 5W30 may be more appropriate for your starting temps.

 

My 2000 TJ 4.0 has an occasional drip from the rear main seal and wanted to try high mileage oil.

All AMC engines leaked. Don't worry about it.

 

Mine likes Castrol 10w30 high mileage.
I did replace my RMS though.

 

Castrol 10w-30 high mileage is $10cheaper at Walmart than AutoZone. Same parking lot. lol

 

I think not using synthetic oil is an old wives tail. I used synthetic in the 4.0 of my 94 Cherokee since it was new. I have never had any oil related issues.

https://www.amsoil.com/p/amsoil-10w-30-100-synthetic-high-mileage-motor-oil-hm1030/?zo=226468

 

Ah yes I knew the miracle fluid would pop up. Nothing wrong with synthetic use in a new engine, however if it's old and tired I question the use. A vehicle with 140K miles that has had unknown oils used in its lifetime would be better off with a conventional high mileage oil. I use Pennzoil high mileage but really brand is up to you.

 

@one bullet, I moved from Pennzoil 5w-30 to 10w-30 high mileage recently in my LJ. However, I also moved to Full Synthetic as well. I've been following The Motor OIl Geek on YouTube and watched this video on high mileage oils. I appreciate his videos because they are more data-driven, and also because he dumbs it down for my simple brain.

 

Thanks for the video lotushunter. I guess what I really want is an oil that will slow down or stop my occasional RMS drip. Synthetic blend or conventional.

 

I ran VR1 20w50 for 120K miles. switched to Mobil 1 synthetic and the RMS started leaking.

I don't think any oil is going help your rear main seal to stop leaking.

.02

 

I've been running Mobil 1 High Mileage 10w40 in my 1991 4.0L HO. Mopar oil filter.

had the rear main replaced at 120K miles. It has 180K miles now.

The 4.0L has piston slap.. so don't worry about thick oil.

 

I use Kirkland Synthetic 5W-30 in my 2001 TJ 4.0. It has a slight leak - like a drop or so per month on the garage floor and it is a little wet underneath. It has been that way for ten years. It may have been worse when I ran dino oil; that was a long time ago. I keep a small cardboard box under it with used paper towels from when I clean the windows; like I said, it isn't a big leak. It is my daily driver.