10w-40 in Jeep 4.0

[blufeb95]

Synthetic is fine you have a 2006 with gaskets made with modern materials, synthetic will be fine, if you want better wear protection and better cold start performance use a 5W30 synthetic, if you're worried about aging seals then use a synthetic high mileage oil.

 

[Redhawk454]

Thanks^

 

[CT Rob]

The Jeep dealer i worked at for 15yrs always used 10w40 in the 4.0 Jeeps

 

[kschachn]

Someone I know said not to use synthetic oil in a 242 since the engine was designed in 1962 and because the tolerances are greater, synthetic oil will cause leaks since it’s smaller on a molecular basis than conventional.

That’s a good one. So you’re saying that synthetic oil molecules are too little?

The old “tolerances” strikes again.

 

[4WD]

That’s a good one. So you’re saying that synthetic oil molecules are too little?

The old “tolerances” strikes again.

This will fill in the molecular gaps

 

[3x4X4]

FWIW my 2006 Rubicon has been fed Mobil 1 10W-30 since new. It now has 140,000 miles and the engine does not use oil at all.

I did replace the OPDA with a Dorman unit when the Jeep was still relatively new because it started squeaking, I think that was around 25,000 miles.

 

[SubieRubyRoo]

There is a whole thread on the Jeep Strokers forum site where they did UOA comparisons on 30w vs 40w oils and there was little difference between them.

Of course there won’t be any differences in UOA comparisons, an oil analysis does not tell you how well an oil protects, it tells you the physical characteristics of the oil after its time in use: Viscosity, TBN, presence of dirt, coolant, or fuel.

Anything else requires several samples to generate trends. If someone tells you they can tell you anything more about how well an oil performs, especially from a single sample, you should run away. Certifications tell you how the oil performs. OAs tell you the condition of the oil in that specific usage case.

 

[quickegt]

I’m in southern IA where we can get those cold winters..

Someone I know said not to use synthetic oil in a 242 since the engine was designed in 1962 and because the tolerances are greater, synthetic oil will cause leaks since it’s smaller on a molecular basis than conventional.

I'm curious when this old wives tale will stop being told.

Synthetic will do no harm to that engine. If you do some research in your free time, you will see countless articles written by people other than "Someone I know" that clarifies this is an old school mentality, that had some validity when synthetics were new and vehicle/gasket technology was old. Times have changed, as have designs and tolerances on engines and gaskets.

As mentioned above, your Jeep is from the 2000's, so you will be fine. The engine has very loose ties, if any at all to the old "tractor engine" that many claim the 4.0 to be.

All that being said, my 2000 XJ currently has 161,000 on it, been running synthetic 5w-30 since about 60k when the vehicle was given to us by the original owner. To this day, I only add about 1/2 qt during my 5,000 mile OCI.

The 4.0 is a pretty stout engine, if you put oil in it, and keep oil in it, it will outlive the vehicle around it. I like using synthetic for the cleaner properties, and the "extended" OCI of 5,000 miles I use.

Happy Jeeping!

 

[KCJeep]

An oil with an HTHS between 3.5 and 3.9 is the sweet spot for the 4.0 IMO. This puts most Euro 5w40s, HDEO 10w30s and PCMO 10w40s as good choices.

Many use 15w40s but I didn’t care for them in mine.

JMO.

 

[wpod]

I’m in southern IA where we can get those cold winters..

Someone I know said not to use synthetic oil in a 242 since the engine was designed in 1962 and because the tolerances are greater, synthetic oil will cause leaks since it’s smaller on a molecular basis than conventional.

Nope.

 

[Building3]

I want to run 10w-40 for my next OCI in my 2006 Jeep wrangler rubicon 4.0

Owners manual recommends 10w30 for decent cold starting and fuel economy but I want to switch to 10w-40 from now on.

I don’t care about fuel economy, I just want my 4.0 to last as long as I can..

4.0 has a little 150k mile.

Is it a bad idea?

I have a 2003 Jeep Wrangler 4.0 in Michigan. Since the first oil change I have used Pennzoil Platinum synthetic 10w-30. It does not leak oil, nor use oil. The oil analysis done from time to time is excellent.

 

[53' Stude]

I’m in southern IA where we can get those cold winters..

Someone I know said not to use synthetic oil in a 242 since the engine was designed in 1962 and because the tolerances are greater, synthetic oil will cause leaks since it’s smaller on a molecular basis than conventional.

What a crock. Another old wives take that won’t ever die.

 

[MNgopher]

Had an 88' Jeep Cherokee with the 4.0 that I ran on Synthetic 5w40 for quite some time. No leaks to discuss from the engine anyways. Note that I did replace the oil filter adapter gaskets once, and the valve cover gasket once, but that was before I used sythnthetic and were done after the vehicle sat for 3 or 4 years before I obtained it.

Basic point is: This had to have been one of the least picky engines about oil. If it had it, it ran fine. I ran anything between 5w30 and 15w40 in it (but not in the winter). 10w30 and up I'd run with no hestitation anytime of the year.

 

[ripcord]

This will fill in the molecular gaps

View attachment 146469

 

[cheesepuffs2]

A UOA isn't going to measure wear and provide comparative oil quality.

I wish this was stickied in this place.