RocketMouse

the coolness factor of being able to use one that literally says Caterpillar on it. lol....

Well seriously, slightly more capacity and filtration... but I'm not sold on the idea for it. Plus I think you have to change out the spindle to convert it if I'm not mistaken.
I say a good quality standard one and change it when it's supposed to and save yourself the extra hassle/expense.

SteveMongr

The oversize oil filters are a direct fit option and are specified to fit and function with the 4.0, no conversion needed. Only a few pennies more than standard size. I use NAPA Gold 1515, made by WIX.

Tbone289

Slightly larger oil capacity, slightly larger filtration media surface area, same price.

RocketMouse

Oh.... I thought I read somewhere that the spindle was a different size for the longer ones. If not... my mistake.

Bugout4x4

From the first days as an AMC they were the same as Ford which was a longer filter. Then at some point the threads went metric and then back again to the original thread. But I'm pretty sure other than thread pitch the bushing size remained nominally the same.

RocketMouse

I think that's what I remember reading somewhere.. I think it was the thread pitch.

And my bad on the oil part. I erroneously stated Rotella T6... then realized what the T6 was... so my bad.
I guess I never thought about running diesel formulated oil like that in a non-diesel specific engine type before. I know Rotella T6 was either top or close to the top of the list on Salad's epic oil thread.

Basslicks

Haha... I mentioned running Rotella to my grandfather and he about had a conniption fit... "You can't run diesel oil in a gas engine, it will clog it up!" The man is brilliant and knows a lot about engines, cars, and a lot about mechanics in general... but I can't get him to wrap his head around the idea that there's nothing in diesel motor oil that will clog up a gas motor. If I ever make the switch to Rotella, I'll just tell him I'm still running Pennzoil.... which for me is still working great in it. Might never switch from it, honestly.

We'll see what the blackstone reports say in another thousand miles or so.

Bugout4x4

If anything Diesel oil has to be a higher quality oil because diesels create even more nasty compounds during the combustion process than gas engines do and the loads are much more severe.

Tbone289

Zinc and Phosphorus levels are the only real difference. Less importantly different viscosity ranges and API standards.

extrashaky

Nobody has provided any scientific evidence whatsoever that diesel oil is better for the 4.0L than passenger car oil.

Now you're saying, "But zinc! Zinc!" Nope, nobody has provided any scientific evidence that the 4.0L needs more zinc than passenger car oil has either. Everybody just accepts the assumption that it does, yet nobody has ever proven it.

Show me a controlled study where a sample of 4.0L motors running diesel oil and a sample running passenger car oil have been analyzed for wear and longevity. It doesn't exist.

All we have instead are anecdotal reports from people who jump on the bandwagon, then convince themselves that the choice they made was "better" because of confirmation bias. They want their choices to be right, so they convince themselves that they are, even though there's no hard evidence that their choice is any better or worse than the guy who uses Mobil 1.

As for that thread, you can write a million words about the zinc content of diesel oils, and it won't make a single bit of difference if the 4.0L doesn't actually need that elevated level of zinc. I could write a million words to convince you that the 4.0L needs to be rubbed down daily with Jergens baby lotion. Wouldn't make it true.

Tbone289

Agreed. It's not bad advice, but it's not based on any factual evidence. The UOAs I've seen with HDEO in the 4.0 are really good, but not any better than PCMO. There have been plenty of 300K+ mile 4.0s run on PCMO 10w-30 oil over there lifetime. Can you really expect any better results from HDEO?

extrashaky

It may not be bad advice. There are two places where I question it:

First, the phosphorus in ZDDP eats catalytic converters. You need enough for your motor, but too much will ruin your cats too early. Cats are not exactly cheap. So why wear it out faster if you don't really need the extra ZDDP?

Second, condensation forms on the interior surfaces of engines when they cool. That moisture causes increased wear during warm up, until the engine is hot enough to boil away the moisture. Detergent packages in oil are formulated in part to bond that moisture to protect engine surfaces until the motor is up to operating temp.

The detergent packages in passenger car oil are balanced for multiple heating and cooling cycles per day, assuming that most people will drive their vehicles short distances, let them cool off, restart them, let them cool off again, etc. The detergent packages in diesel oil are designed for long distance driving of 500+ miles per day with many fewer heating and cooling cycles. Motor oil also breaks down differently under long haul conditions, so the volatiles that are created are different as well.

So if you're putting diesel oil in your Jeep and driving it as a daily driver to work, to lunch, to the store, back home, to the mall on weekends, to a restaurant, all around town, etc., you have a detergent package that is not optimized for the type of driving you're doing. Is it detrimental? I don't know, but logic would seem to dictate that it's not the ideal choice for managing condensation in your motor.

So maybe it is bad advice. Or maybe these concerns don't matter. Nobody really knows, since nobody has done the scientific work to prove it one way or the other.

The way I look at it, the manufacturer does not recommend diesel oil for this engine. They're not perfect, and part of that may be the result of regulatory requirements, but they have done more product development and testing than anybody trying to sell you on using diesel oil. Until someone can show me actual scientific evidence that the manufacturer is wrong, I'm sticking with their advice.

Tbone289

The manufacturer also was not recommending oils with today's PCMO API specifications either...

Are today's PCMO API specs as good for this engine as the PCMO specified in 1987, or are today's HDEO specs with higher zinc closer to the 1987 API specs? As I understand it, modern API specs call for reduced levels of zinc, due to orders from the EPA. There's another question for you, and it's very similar to the age-old DEXIII vs ATF+4 argument, or how many licks does it take to get to the center of a Tootsie Pop.

This can all be easily over-thought, IMO.

extrashaky

Jeep was still recommending passenger car oil for the 4.0L up through 2006, which I believe was after the mandated reduction in phosphorus.

Actually, the "high mileage" passenger cars oils typically have pre-reduction levels of ZDDP. So even if someone established scientifically that our motors really did need the extra zinc, that still wouldn't necessarily mean you would need to use a diesel oil not intended for daily driving.

But I still don't know why we're worried about that question, when nobody has ever answered the more important question of whether the engines really need it.

Tbone289

I'm aware of that, and I'm not aware of any manufacturer who has likewise not done the same. However, the 4.0 was designed long before the reduction in zinc. How much time do you think is spent by manufacturers to re-analyze the long-term effects of a new API spec on an old engine design? Very little, I would imagine. They recommend what is most convenient to them, just as they did with ATF+4, as I mentioned above.

My point really is the same as yours, that you can make all of the guesses or assumptions you want as to what is best, but it's a waste of time if you don't have any facts to back them up.