Which oil & fluids for NEW jeep 4.0 I-6

[Stainless]

A friend of mine JUST bought (35 miles on the odometer when it made it BACK to his house) a brand new Jeep. It is a 2006 Jeep wrangler with the 4.0 liter INLINE 6 cylinder. He plans on being the first, last, and ONLY owner.

This engine will see cold ohio winters(sometimes it gets down to 0 and below at night), and warm ohio summers (sometimes above 90).

What oil would you guys run? The manual recommends 10W-30. I was thinking regular Mobil 1 5W-30. Whatever oil my friend decides on, will be the ONLY oil he runs for the LIFE of the jeep... so I wanna help him make a good decision. That's why I thought Mobil 1 5W-30. It is SM rated, it is easy to get at walmart, and since the vehicle is still under warranty it is a well known name.

ALSO, he was thinking about changing transmission fluid, and all other fluids to synthetic. What tranny fluid (it's a 6sp manual), differential, etc etc would you all recommend?

thanks.

 

[toneloc12345]

Seems like a lot of people on here with 4.0s like to run a little thicker oil. Rotella 5w40 may be a good choice. Seen plenty of good UOA's with havoline 10w30

 

[sw99]

A lot of todays 5w30 are better than 10w30's. I personally run 5w30 pretty much rear round and have no issues. The Wrangler I just sold have well over 100K and I did the same with that vehicle. Oddly enough, the jeep is quieter now than when I was running the 10w30. The owners manual still specs it for lower temps.

 

[Eddie]

My 1995 4.0 Grand C is still running great at 197,000 miles. No valve cover or oil pan off, ever. Whole life on Mobil 1 10w30 & PureOne oil filter every 5 - 6,000 miles. Today I would go with Mobil 1 5w30 Truck & SUV oil.

 

[Oil Changer]

I hate to say this, but if it were mine and under those circumstances, I'd use Amsoil's (ATM) 10W30. For gear oil, I'd use Amsoil's (SVG) 75W90. I don't know what the manual says to use for the MT but I would suggest Amsoil for that too. If he's going to do all of that, he might as well use Amsoil grease also. All of this can be delivered to his door.

 

[MNgopher]

I'm seeing several recommendations for 5w30 year around, but based on my experience, I've chosen not to go that route (even though it would simplify my oil supply!).

My '88 Jeep Cherokee with 4.0l gets 10w30 in the summer, 5w30 over mostly winter periods. I've found under sustained highway driving that my oil pressure is substantially lower using the 5w30 in higher temps as the oil change interval progresses. That being said, the oil pressure never drops below spec, but relative to the 10w30 oils, the pressure change is noticeable.

I used to run the 5w40 Rotella T, but stopped for two reasons: 1. I felt this vehicle was short tripped to much to benefit from the thicker oil and 2. It meant going to Wal-Mart, and that was literally the only thing I ever bought there!

Perhaps the synthetic 5w30's being usuggested my be just fine, but primarily 10w30 oils have serviced this excellent engine for a long time very well.

 

[Sparkman]

I think 0w-30 GC is an ideal oil for this engine for most applications. It has good cold flow characteristics while being a relatively thick 30, which the 4.0 seems to like. I have a 9k mile GC UOA that showed good wear, though I don't think that GC is an excellent long-drain oil in this engine.

I will probably stop using 5w-40's in my 4.0 due to my current short trip use. This winter I'm using the thinner Amsoil s2k 0w-30.

 

[Brian Barnhart]

I've used 5W30, 10W30, and 5W40 in my 4.0. 10W30 seems as good as any in the 4.0. Using a 40WT will reduce fuel economy noticeably. When using 10W30 in Ohio winters, I always use a synthetic.

If the transmission is anything like the 5 speed AX-15, I would strongly recommend using the OEM fluid (which I believe is partially or fully synthetic) in the transmission. I've tried several synthetics in mine and all made shifting rougher and more difficult than the OEM fluid specifically designated for that transmission.

Synthetic 75W90 gear lube seems fine in the front diff. And M1 synthetic ATF works good in the command trac transfer case.

If you have limited slip in the rear, I recommend sticking to OEM fluid with LS additive and change at least every 50K. In a non LS a synthetic gear lube should be fine.

 

[Sparkman]

Quote:

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Using a 40WT will reduce fuel economy noticeably.

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That depends on the type of use. For short trip use yes, when I was driving 110 miles a day it wasn't even noticeable.

 

[Zaedock]

Your 4.0L will probably run forever regardless of what you put in it. Personally, I use 5W30 in winter and Delo SAE30 or 10W40 in summer. Thicker is better for me, although his TJ probably won't see the same conditions as my YJ.

If he wheels, synthetic diff fluid is a waste. If he doesn't (which is a shame...lol), I see no reason or benefit of swapping out the factory fluids.

 

[Flipside]

This sounds like it could be ME! Except my TJ had 40 miles on it when I got home from the dealer... Most of my miles are short trip, and I live in Wisconsin. So temps can hit extremes on both ends of the scale. Any recommendations for short trip (<10mi) use?

 

[Gary Allan]

Apparently timing chain wear is the item that sticks out in UOA in the 4.0/2.5 engines. It doesn't seem to be totally viscosity related. The bottom ends are pretty stout (very, actually).

I've never seen any appreciable fuel economy difference in the Wrangler w/4.0. That is, it doesn't seem to give a hoot what you're doing (much anyway). Even with a Warn lock out hub kit and swapping to synths in the diffs, it may have altered it 1 mpg on a fairly consistant basis. Both (the kit and the fluids) DID make a difference in rolling effort (higher down hill coasting achieved and more perceived power/less drag) ..but none of it translated to fuel economy. The engine just develops way too much power at a very low speed to be much of a fuel squeezer, imo. My wife commutes @ 60 mph. She may break 19.5. If she does soccer mom type duty ...17.5. It's not like some engines where you'll get 22 around town ..and up to 30 on the highway cruise. I'm sure aerodynamics has an impact ..but not as much as one would expect in the case of the 4.0. You get no ROI no matter which way you turn in terms of economy.

In my 2.5 I use RTS. It's not performing as I expected, but I had some ignition issues that could have been aggrevating some Fe production. The oil is near bulletproof, imo.

Nothing is static in terms of oils. It used to be that you could see higher Fe with lower visc oils. The only exception being that someone with short trip usage would see lower Fe readings ..but they were actually at a higher visc due to the shorter trip usage.

Now we're seeing very good performance out of some 10w-30 and 5w-30 oils even in sustained full warm up usage. This suggests that certain additive packages can contain the valvetrain wear without being heavier. My experience with RTS indicates that viscosity alone won't inhibit the Fe wear in the face of some other conditions. I'll know the next UOA

 

[JohnBrowning]

If he is worried about Waranty then he should stick to 10W30. M1 10W30 or M1EP 10W30 would be good choices but so would all of the other name brand synthetics like PP. Once his warranty is up he will more then likely find that this engine likes a 40Wt. oil better then a 30Wt. and Rotella-T Synthetic 5W40 is very popular because it works great and is priced right!Now if he does not go the synthetic route then I would definately go with Chevron SUpreme or Havoline 5W30 for winter!

 

[Rand]

I used m1 t&s (5w40) in my 2002 ranger 4.0 and the fuel economy wasnt noticeably different.
maybe at MOST .25mpg

 

[MarkC]

10W30 Havoline is working very nicely in mine.