Oil for Jeep 4.0 Engine

[KCJeep]

Several recent UOA's (one of them mine) have shown while the 4.0 will run well on 5w30, it doesn't really care for it wear wise. This is an old engine design and thus the reason for the 10w30 spec. "Thick" 5w30's like the Defy mentioned should be fine but I'd avoid most and stick with 10w30 at least.

A lot of testing by myself and another Jeeper here has found PYB runs exceptionally quiet in the 4.0, I believe it's the high moly whatever the reason they like it. Other real good choices for the 4.0 are Valvoline, Rotella and Defy, they consistently produce very low wear numbers in the venerable 4.0.

I lean towards thick but 15w40 is overkill IMO and jumping from that to 5w30 is too drastic. A move to plain old 10w30 Valvoline or PYB will be much, much thinner than the 15w40 and accomplish what you desire for start up AND maintain better protection than most 5w30's. Most 5w30's are actually fine, at first, but once they shear which they inevitably seem to do they are too thin for the 4.0, thus the 10w30 spec.

I am running PYB 10w40 in mine now but it's actually thinned with a quart of 5w20. Love the way it runs on any grade of PYB though.

 

[AmishFury]

Originally Posted By: buster
Mobil 1 High Mileage 5w30 would be a good fit. SL levels of ZDDP.


UOAs in the 4.0 show higher than usual iron for that oil

i can't help but recommend QS Defy or PYB... i'll let you know at some point how PU does in the 4.0 but i've still got another 1K on the current OCI

 

[Kuato]

I've had very good wear numbers using Amsoil, VWB and even ST Syn, all in 5w30. 10w30 Amsoil got the same wear numbers as the 5w30.

Haven't tried a xxw40 in our 4.0.

 

[TXCarGeek]

Originally Posted By: AmishFury
Originally Posted By: buster
Mobil 1 High Mileage 5w30 would be a good fit. SL levels of ZDDP.


UOAs in the 4.0 show higher than usual iron for that oil

i can't help but recommend QS Defy or PYB... i'll let you know at some point how PU does in the 4.0 but i've still got another 1K on the current OCI


I'm really wanting to run PU or PP in my 4.0 next oil change. I would love to hear how yours does on it!

 

[SwampSurvivor]

Originally Posted By: TXCarGeek
Originally Posted By: ChemicallyChargd
Well to clear some confusion, I won't argue zinc benefits flat tappet rides, but there's some confusion as to why or how. Zinc is not in any way nor does it form any kind of magical coating on parts, a high zinc level will only allow the motor oil to last longer before it's supply of zddp is depleted. Using a motor oil that has such a zinc level that it can't be API certified or adding it in has been proven to do more damage to your cat's, far more damage than its worth, like trading your dollar for a penny. So essentially don't worry about the zddp, if it's API certified it's got plenty zddp to last through a 5k-7,5k mile OCI, it would only concern me if I were considering 10k+mile OCI' s(what I do currently). Shear strength is the single most important thing you want, if this sucks, it defeats the point of a good additive pack. Take it all the way and use their 0w-30, the viscosity at room temp is closer to the operating temp viscosity, which means less viscosity modifiers and a higher total base stock % (less additive means more actual oil), both being the same op. temp viscosity, the 0 will get moving quicker at lower temps than the 5. Remember the problem with oil is it thickens when it cools, NOT that it thins when it gets hot, the 0w thickens less, if nearly all wear is in those few seconds at cold start(after its warmed up the oil can get moving almost instantly and can be started/stopped with no where near the wear of a cold start), and the 0w gets to your bearings faster, it's the intelligent choice.
-SRV


I ran M1 AFE 0W-30 in my TJ from July-March this past year and it did fine on it. After looking on here though, I saw that for the temps that I see here Texas, at start-up, the 5W and 0W viscosity were [censored] near the same. It wasn't until extreme sub-zero temperatures that the cold cranking advantages of the 0W came in to play. Because of this and the lower zddp levels in M1 AFE, I switched back to M1 5W-30. Has the same viscosity in the temp ranges that my Jeep will see and a bit more zddp.


My jeep starts fine and makes no funny noises on -30 nights with RT6 5w40.

 

[6lbsoft]

You guys wanna hear something scary? Buddy of mine used to have a 88 Cherokee with a tired 240,000 mile 4.0 in it. After the oil pressure got down to 8psi at idle he decided to do just change out the bearings with the engine still in the car and throw in a high volume oil pump. After this he ran Kendall Nirto 70wt racing oil in it... 95psi pressure when cold and revved up lol! Needless to say he got another 30k out of the engine before selling the Jeep. Those engines are pretty tough.

 

[KCJeep]

Originally Posted By: TXCarGeek
Originally Posted By: AmishFury
Originally Posted By: buster
Mobil 1 High Mileage 5w30 would be a good fit. SL levels of ZDDP.


UOAs in the 4.0 show higher than usual iron for that oil

i can't help but recommend QS Defy or PYB... i'll let you know at some point how PU does in the 4.0 but i've still got another 1K on the current OCI


I'm really wanting to run PU or PP in my 4.0 next oil change. I would love to hear how yours does on it!


I'm itching to do a run of Ultra 10w30 in mine but I have too much oil. Of the two though I think the Ultra is a better looking match for the 4.0 than PP. It has higher HTHS and the GTL base 10w30 should be much more resistant to shear, both good things for the 4.0.

I wish you hadn't a said that now I've got an Ultra itch again!

 

[TXCarGeek]

Originally Posted By: KCJeep
Originally Posted By: TXCarGeek
Originally Posted By: AmishFury
Originally Posted By: buster
Mobil 1 High Mileage 5w30 would be a good fit. SL levels of ZDDP.


UOAs in the 4.0 show higher than usual iron for that oil

i can't help but recommend QS Defy or PYB... i'll let you know at some point how PU does in the 4.0 but i've still got another 1K on the current OCI


I'm really wanting to run PU or PP in my 4.0 next oil change. I would love to hear how yours does on it!


I'm itching to do a run of Ultra 10w30 in mine but I have too much oil. Of the two though I think the Ultra is a better looking match for the 4.0 than PP. It has higher HTHS and the GTL base 10w30 should be much more resistant to shear, both good things for the 4.0.

I wish you hadn't a said that now I've got an Ultra itch again!


If I end up going with Ultra, I'm going to use 5W-30. I like the thinner viscosity of the 5W for cold starts.

 

[salv]

The Pennzoil site recommends PYB over their synthetics for the 4.0. Every other vehicle I put in, they recommended a synthetic for optimal protection. Perhaps there is a such thing as too slippery for the flat tappets?
I like the way my 4.0 runs on cheap dino. 15w40 has worked fine in my 4.0 this past run. It was a little thick for northern NY in March, still below zero in the morning. 50 degrees seems about where the difference in startup goes away.
Mobil Super High Mileage 10w30 has run the best in mine, followed by Peak 10w30 and Formula Shell 10w30.

 

[crazyoildude]

my brother uses 10w30 pyb in the winter and 10w30 phm in the summer and it runs good

 

[901Memphis]

10w30 is obsolete.

 

[KCJeep]

Not in the Jeep 4.0 it isn't, it's the primary spec oil and for tangible reasons too. It's also the only spec oil in the Jeep 4.7 HO and a few other rides as well.

And good ol 10w30 works well in almost anything to boot.

 

[47HO]

KCJeep is correct.

 

[84zmyfavorite]

Oooh, oooh,..I currently have 7 Cherokees, 5 of which have the 4.0, I have ALOT of Respect for this engine, so I recommend what I think is the Best oil for them, and that would be Valvoline Maxlife 10w-30 if Shes HighMileage and a bit leaky, Shell Rotella T5 10w-30 if no leaks. Perfect Oils for the 4.0 in nearly every temp.

 

[84zmyfavorite]

Im Glad to see other people say PYB, because I too have noticed how 4.0s run on it, and its similar to how they Run and Feel on German Castrol(0w-30). I just dumped 6 quarts of PYB 10w-30 out of my 99s 4.0 that was break-in oil for almost 1200 miles(of 1300 miles total on ReBuild, it was the 3rd oil change, 1st at 30minutes, 2nd at 40 miles) and I dont think for Break-In, I could not have chosen a better oil. I am sending a sample to BlackStone and will post results. My 1st vehicle ever back in 2000 was a 89 Black Jeep Comanchee with a 121,??? mile 4.0 that had been serviced religiously with Pennzoil 10w-30, and man that 4.0 ran, idle and performed like she had 50,000 miles.

 

[Challenger71]

I currently have ultra 5w-30 in my 4.0L 2001 XJ and I like how it performs. Has shown one of the higher oil pressures over nearly all other oils I've used in the past. Oil pressure usually in the 40-50 psi realm under load. Use it with a RP oil filter. This particular OCI I also added a dose of LM Ceratec and this has improved NVH.

 

[SuzukiGoat]

Originally Posted By: KCJeep
Not in the Jeep 4.0 it isn't, it's the primary spec oil and for tangible reasons too. It's also the only spec oil in the Jeep 4.7 HO and a few other rides as well.

And good ol 10w30 works well in almost anything to boot.



Exactly...sorry, if I'm using zero weight or five weight you can bet that second number is a 40-60...

4.0L pump out a LOT of heat. You wouldn't catch me without a 5w40 syn or 15w40 or sae30 in it. Leave the 0 and 5w20-30 for people who actually care about fuel mileage.

My friend had a 91 with 260k miles he parted with in 08...it ran rotella for its entire life. The only thing on it that worked as it should at the end was the motor.

Of all the people who I know who have 4.0s in Cherokees or regular Jeeps,all run 15w40 and have at least 180k miles.

 

[84zmyfavorite]

My 87(First year 4.0) has 297,525 miles on her original everything, has been abused before I got it, and runs(and drives) as if She only has 100,000 miles. 7,000 to 8,000 miles before I change the oil from her 4.0 because it dosent even turn Brown until then, more like alight tan. Smooth, High compression, powerful 1st year 4.0! Currently filled with..Gasp..Shell Rotalla T1. Yep 30 weight T1. My 96s 4.0 has a bit over 250,000 and is the same way, though when warm with a synthetic(dosent seem the matter which kind from SuperTech 10w-30 to 300V Chrono 10w-40) ahs a light lifter tick, that goes away with a 30 weight. If temp permitting, I prefer to use 30 weights in older HIGH mileage 4.0s.

 

[Challenger71]

slight correction to my orig post: should of stated 55-60 psi.

Originally Posted By: Challenger71
I currently have ultra 5w-30 in my 4.0L 2001 XJ and I like how it performs. Has shown one of the higher oil pressures over nearly all other oils I've used in the past. Oil pressure usually in the 40-50 psi realm under load. Use it with a RP oil filter. This particular OCI I also added a dose of LM Ceratec and this has improved NVH.

 

[aaonms]

1999 Jeep Wrangler with the mighty 4.0 here too.
I am the original owner and live in northeast Florida so it gets warm here.
Some moderate trail riding these days, but hard core off roading is a thing of the past.
It is not my DD, more of a weekend toy now and owing to this, Oil Changes are usually once a year as I typically hit the 5000 miles mark at about that same time.
To make a long story only slightly shorter, I have been using Blackstone for UOA since 2003 (28,882 miles on the Jeep/Motor).
Oil of choice then was Mobil 1 10W/30.
Over time, the Lead trended up for the motor as well as compared to Universal Averages.
At first, Blackstone suspected a particle streak and not bearing related. Other values looked good.
Flash forward not quite five years to 2008 (48,553 miles) and there was a substantial increase in Lead as well as in Copper and Tin.
By 53,306 miles in 2009, Lead stabilized, but was still high. At this point, Blackstone recommend I consider switching brands of oil or moving away from synthetics.
I switched to Valvoline SYNpower 10W/30 and Lead came down for a bit, but is again on the way up.
Blackstone’s comments from the most recent Oil Change that had 4121 miles on the oil, total mileage 69,503 was: Not a lot of change since 2011, though you are getting a little more bearing wear than you used to. We've seen lead out of this engine before, and it didn't amount to much, so maybe it will drop again. We're a little concerned, though, seeing copper and lead both reading high. Typically this shows bearing wear and it could be the result of hard operation, or it could show a problem brewing. This engine is known for antifreeze, though it's hard to say for sure because the sodium in this oil masks sodium that might be coming from coolant. Stay at 3K-4K miles to monitor.

Am considering dumping the oil at 2000 miles, sending a sample to Blackstone, and also changing brands again.
I had good results with Rotella in several VW’s (both turbo and NA) and am also pleased with the German Castrol in my current turbo MINI.
While it pains me to think non-synthetic may be the way to go, some readings here and on several Jeep Forums makes me wonder if this may not be the way to go.