5w30 in a Jeep 4.0L

[Nick1994]

So I have always heard on here about how 5w30 and 0w30 are completely compatible in 10w30 applications. BUT, I recently saw on a thread where a couple people said to use 10w30 in a Jeep 4.0L, that it would shear down a 5w30.

Why is the 4.0L the only exception where it's recommended to not use a 5w30 in it? I ask because I have lots of Castrol GTX SynBlend 5w30 in my stash for my grandfather's 96' Cherokee with the 4.0L that I maintain and my brother has a 91' Cherokee with the 4.0L and he too has lots of the same oil in the same weight waiting to go in there. Also my grandfather's Jeep currently has the PurePlus Pennzoil Platinum 5w30 in it (it gets a yearly oil change, about 3-4k miles per year).

So, is it not very safe to use 5w30 in a 4.0L? What if it were for 5k miles?

 

[DoubleWasp]

Use a 5/30 with better shear resistance.

 

[zach1900]

I had a 2000 XJ 4.0 and it actually seemed the quietest and happiest on Pennzoil yellow 10w30 year around.

 

[zach1900]

The difference between 5w and 10w are negligible, or so I'm told.

 

[147_Grain]

IF I had the 4.0L engine, I'd be running Mobil 1 0W-40 / Rotella T6 5W-40 synthetic or for conventional / synthetic blends, MaxLife 10W-40, PYB 10W-40 or HM version, or Mobil 5000 10W-40 +/- HM. Some folks are also running high mileage 5/10W-30 oils (synthetic or a blend) in their Jeeps with acceptable results.

 

[Chris142]

In the past uoa's showed 10w30 and 10w40 showed less metal than 5w30.

 

[DoubleWasp]

40 weights hit the fuel economy pretty good. Ask me how I know. I just changed mine over to VR1 Syn in 10/30. What a difference.

 

[Finn]

With 135k miles on the clock mine seems to like synthetic 5W-40 better than 10W-30.

 

[zach1900]

My XJ is one of the few cars I regret selling, and it only had 70,000 miles, young for an XJ inline 6.

 

[Dyusik]

I dump in T6 once a year and call it good. And as for fuel economy ....IT'S A AMC 242! What economy ??? lol

 

[zach1900]

True!

 

[901Memphis]

Originally Posted By: Chris142
In the past uoa's showed 10w30 and 10w40 showed less metal than 5w30.


Yes I noticed this too, which is something that isn't easily explained. I previously guessed that the higher HTHS offers better protection, or maybe the 5w30 just can't maintain an adequate film thickness when hot.

 

[19jacobob93]

Originally Posted By: Nick1994
So I have always heard on here about how 5w30 and 0w30 are completely compatible in 10w30 applications. BUT, I recently saw on a thread where a couple people said to use 10w30 in a Jeep 4.0L, that it would shear down a 5w30.

Why is the 4.0L the only exception where it's recommended to not use a 5w30 in it? I ask because I have lots of Castrol GTX SynBlend 5w30 in my stash for my grandfather's 96' Cherokee with the 4.0L that I maintain and my brother has a 91' Cherokee with the 4.0L and he too has lots of the same oil in the same weight waiting to go in there. Also my grandfather's Jeep currently has the PurePlus Pennzoil Platinum 5w30 in it (it gets a yearly oil change, about 3-4k miles per year).

So, is it not very safe to use 5w30 in a 4.0L? What if it were for 5k miles?


The Jeep is not the only exception! Same as my Falcon which also happens to have a 4.0 I6. Ford specced 5w30 for the 1998 series 1 and then in 2000 for the series 2 they changed it to 10w30 on the exact same unchanged engine. Sounds like leaping backwards but there has to be a reason behind it. I think the reason is they also gave it a new 15,000km OCI, and 17 years ago, a 5w would probably shear to nothing after 15,000km although these engines tend to be very easy on oil

 

[Oil Changer]

It's been a long-standing and appalling trend for members of this forum to (what I call) parrot responses. That is, someone reads that 10W-30 worked good in a certain application, they repeat that in another thread when someone asks, "What is best..." and poof, it becomes fact even though (more often than not) don't and never owned that particular engine nor actually used the product themselves. This is how we have darlings on this forum like TGMO and MaxJunk, oops, I mean MaxLife. I got caught up in the hype once, strayed from my routine, and feel I got burned. Now I stick to my experience and instinct.

You have the luxury of living in a warm climate. You are free to experiment with the entire gamut of available oils. 10W-30 might be best for your application but only you can tell us what is best for you after long-term experimentation, trends, and gut feelings.

Furthermore, in your case, some members will speak from both sides of their mouth. One thread they will say 0W, 5W, and 10W are all 30 grade so you can use any BUT the 4.0 "eats up" and "just loves" 10W. So which is it?

Caveat emptor

 

[Oil Changer]

In the past and today as well. For the longest time I used Amsoil's HDD as the benchmark to compare other 30-grades to. I've never seen a bad report on HDD. Thin proponents will say UOA is invalid. Tell Blackstone that. They have thousands of engines in their data pool and you can extrapolate what works well in certain applications. They will tell you the sum of their universal averages for your application if you ask them.

Unfortunately, this site is trendy. It's cyclic. Right now (especially since it's winter on this side of the globe) it's thin to win. Come summer, it will cycle back to heavier oils.

According to another industry-insider and engineer member, 3.5 is the natural HTHSV for 30-grade. But since we are in a thin cycle, that's too heavy, even if your engine calls for a 30-grade and may respond nicely to an oil with an HTHSV of 3.5 (or greater).

Unfortunately, sheeple need to be told what to do. Critical thinking and common sense went out the window long ago.

Originally Posted By: Chris142
In the past uoa's showed 10w30 and 10w40 showed less metal than 5w30.

 

[toneydoc]

Hi Nick
I too maintain a 4L I6 in a Jeep. Have for 21 years now. Not one time to an oil change facility. Only my garage.
It has been in the USA and I took her to Europe for 6 years while in the service.
I changed the oil over there at an auto craft shop using USA branded oils purchased at local US base.
It has had a diet of 5w30, 10w30, and 10w40 oils and lately I have added in some 0w20 synthetics into my mix. The engine runs great. Starts right up. Does not use but maybe 1/3 quart over 4k miles.
You can use the 5w30 oils in your stash and they will work really well in that engine. The key is you are doing good yearly oil change and using good product.
Your grandfather is lucky to have you help him. Keep up the good work.
Too many young folks do not have time for the older folks any more. I am glad you take time to help him.
Back to your question about the engine, it is really easy on oil. It is a really good engine when properly maintained. Take good care of it and it will last your grandfather a long time.

Thanks for helping him
Bob

 

[Kira]

Hello, Simply an anecdotal tidbit here but my sis' 4.0L (in a '99 XJ) got nothing but 5W-30 dino in a 4 season climate (No. N.J.) and purred at 171K when sold.
I suppose the engine would've been OK with 10W-30 during warmer months.
I suppose synthetic would've been better all the while.

To DoubleWasp: How much difference in mileage did you note? I'd love to know. Kira

 

[dlundblad]

I think anyone would be fine with a 5w30 if they just kept the intervals short. (No more than 3k)

You bought all that oil on clearance so I would use it worry free. Since its your grandpas Jeep, is it short tripped? Maybe the 3k OCIs are best anyways.

If you were going to the store to buy some, I would recommend a 10w30 only because you can stretch the OCI to 5k and get more bang for you buck.

As far as UOAs, I remember seeing a decent one on 5w30 a while back. I doubt running 5w30 at 3k vs. 10w30 at 5k would affect the life of the Jeep.

 

[SwampSurvivor]

I am a huge fan of 0w-xx oils.

I think with the Jeep 4.0, 10w-30 seems to be the data driven best choice. Look at the UOAs. For some reason 10w-30 gives the best wear numbers. Sometimes, data can prove wrong what you feel. This is a case of that.

For 2 years, I ran RT6. Got a good ~1.5 or so MPG back by switching back to 5w-30 PYB. I avoided 10w-30 until I did a pour test comparing RT6 and 10w-30. At most temperatures, the RT6 is THICKER (we're talking down to 0F. ..) than the 10w-30. My next OCI on the cherokee will be 10w-30 of some sort. Thinking of Supertech high mileage, Supertech synthetic - both with moly additives - or PYB 10w-30.

Wish I had pulled UOAs on this thing all along. The 5w-20 blend would have been interesting!

 

[Donald]

I run PP 10W30 in my Jeep 4.0. Tried T6 but it did give a small hit to fuel economy. Cold weather cranking is not an issue with
synthetic oil.

I would run 5W30 to use it up if I had some extra. But I would not buy any.