n00b here...what oil for my 4.0L Jeep?

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Apr 28, 2003
Katy, Texas
I've been reading through the forum....lots of information. I'd like to get more life out of my Jeep and could use some help. I currently run Penzoil with a Fram filter (Wal-mart oil change) but I wanna start changing it myself. The dealer used Valvoline with a Mopar filter, better combo. I use 10w30 conventional oil. My 4.0 has 138K miles on the clock and I do alot of stop and go as well as cold start and have to go 50 mph right after start up. Any oil suggestions? Thanx!
Our 2001 has 10W-30 recommended. We ran it thru about 3-5000 on dino, then switched over to M1 10W-30. Have since switched to M1 0W-40.

If you plan to run dino, then some suggestions will come your way. I've been using synthetics for about twenty years, and switch everything over to that.

Either way, do a search on oil analysis, consider having a sample of your current oil done and go with the recommedations.

My 96 ZJ 4.0 now has about 120,000 miles on it. I'm currently running a treatment of Auto-RX using Mobil Delvac 1300 15W-40 and a WIX/NAPA Gold filter, (FRAM PH8a size). The 4.0 motor has lots of piston slap, and always has. This doesn't see to affect longevity at all. The 4.0 will easily see 200,000 with abuse. Many go 500,000 plus with reasonble maintenance. If your weather will tollerate it, I would run a good 15W-40 oil (like Delo, Delvac, or Schaeffer's) and change the oil and filter every 5000 miles. You can run oversized filters on your Jeep. I like the WIX filter (same as Carquest and NAPA Gold) due to its high-quality components and quality construction. I also like the Amsoil filters. Like a said, I run the large Ford equivilant sized filter (FL1a/FRAM PH8a) or if I'm really treating my ZJ nice, I'll run a WIX 51773; this baby holds about a quart of oil!

The 4.0 is a great, if not crude motor. Aside from its piston slap issues and its chronically leaking rear main seal, these are great old-school engines. Now, if I could only say the same about he shi!@Y transmission and rearend...

Edit: Just adding stuff.

If your weather is cool, use a good quality synthetic 10W-30. I like the Amsoil oil, and have had awesome used oil analyses results using it for extended (24,000 miles on same oil) changes. You can beef this oil up some by adding some Schaeffer's #132 Mole E.P. Oil Treatment to the Amsoil at a rate of approx. 1 oz. 132 to 1 quart oil. This will also quite the piston slap that the Amsoil 10W-30 (or other 10W-30s) won't. This engine is extremely easy on oil with its large 6 quart sump and loafing around nature.


[ April 29, 2003, 10:27 AM: Message edited by: darrenc ]
My 89 Jeep Wagoneer /w 4.0 saw 150k miles before trading it in and it was running strong then.

I didn't do anything special. Stock size Purolator filters with Castrol dino 10w40 since about 75k.

I would check the vacuum lines, pcv stuff and other maintanance items before spending money on fancy oil. I replaced my lines at 120k and noticed a huge performance and economy difference. I also switched to better injectors and got real gains, but that's a little more involved.

4.0s are great motors. They really can go forever. I would just keep giving it dino and possibly try the autoRX.
I have two Jeeps..99 Cherokee and 01 TJ...both 4.0L.I use Mobil 1 10W-30 and Purolater Premium Plus Ford oversize (P30001)oil filter on both since break-in.The Mobil has greatly reduced the piston slap on the Cherokee and the TJ never really had any (musta got lucky)but with your mileage sometimes the "ever reluctant to keep oil in the motor" rear main seal might start to weep.I would take a look at the rear main and see if any "sweat" is in that area.If so I wouldn't go with a synthetic but either Castrol GTX or Pennzoil...both in the 10W-30...good moly counts in those two oils...and a quality oil filter...oversize is up to you.I found that the Ford filter was a tad leess expensive than the standard Jeep issue and it's bigger so it was a no-brainer for me.I've used Mopar,Mobil 1,Wix oil filters and just like the Purolaters.Darrenc..what tranny?rear axle do you have?The AW-4 tranny is a joint venture with Toyota and Borg-Warner and are a very stout unit..if you have the Dana 35c then I can see problems with those under heavy useage.
Wow, thanks y'all....y'all sound like the JeepsUnlimited.com guys when it comes to Jeeps;very helpful!!! Well, this ZJ has been through alot, Tropical Storm Allison, my mom's hard driving habits (used to race cars over seas) and now me. The rear seal was replaced under warrenty at about 40K. The Dana 35c has been great, no probs, even with the water that was found in the diff (which my dad stupidly changed a year after the Storm). The tranny, its brand new. Overall, best vehicle our family has owned...for the new cars, we'll see. 10w30 is best down here in Texas. Whats a good brand of 10w30... i heard something about Moly? I was reading at about 11:30 last night.
...If the rear main has been done at 40k and there's no hint of oil...go for the synthetics

The 96 and up ZJs went to an in-house DC 42RE tranny. I've heard that this was done for smog reasons; it's electronically controled/OBDII. You're AW-4 is an awesome tranny. Can't hurt it. The 42RE is an aluminum cased torqueflight derrivitive that uses a four gear aluminum planetary. With a good pro rebuild, they can be made very robust; however, the standard DC innards are crap. Mine's been slipping for about 15 K miles. We'll be doing a rebuild soon.

My Dana 35Cs have been rebuilt twice. Once because of faulty carrier bearings and miss aligned pinion gear, the second time because of a botched repair the first time.
The power steering pump went out at 80K. The water pump and tranny rear main seal and the upper control arms on rear axle at 90K. The exhaust manifold at 105K, and the catalytic converter at 117K. It's a Jeep thing! Despite all this, I still like the rig.
Sorry 'bout all the miss spellings. It's late.

Correction..... All late 93 and up ZJs had the 42RE if you got the 4.0. Early 93s, like built in 92, had the AW4.
Not too sure on the history since it was built for AMC and the original cherokee. I know its tough but when it breaks, a rebuild is not recommended. I know its good...when i convert to 4WD, im gonna probably throw in the AX-15 that was avalible on 93 and 94 ZJs since stick shift is cooler.

Originally posted by darrenc:
Thanks for the correction. Aren't the AW-4s made by Aisin Warner?

Aisen/Warner tranny was a joint venture with Aisen (who manufacture Toyota trannies) and Borg Warner that lasted for years...great tranny.

Originally posted by JeepZJ4.0:
Not too sure on the history since it was built for AMC and the original cherokee. I know its tough but when it breaks, a rebuild is not recommended. I know its good...when i convert to 4WD, im gonna probably throw in the AX-15 that was avalible on 93 and 94 ZJs since stick shift is cooler.

The Chrysler TorqueFlite 904 auto's were an option behind the 4 bangers and the 999 behind the V6 Chev. engine until 1986.They disappeared for a few years with the 904 reapearing in 93 and the 30RH in 1994.The 4 banger had the 30RH and the 6 had the 32RH...these are both stout trannies...then the AW-4 was mixed in among them around 87 and up...and the AW-4 was called AW-30-40 at that time...crap load of trannies EH!
Getting back to oil..... I've been reading alot about Chevron... I've always liked their motoroil, i guess it was the nice blue bottle. Is it really good for someone like me who does stop and go?
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