So it's been about 300 miles, and I'm changing out my oil/filter. I decided to go with cheap oil for the first 300 - 500 miles, just to give the engine a good bath in something clean for a little while. Now it's time to put the real stuff in.

Guy at work suggested high mileage oil. My Jeep has 170k. I don't know if that could be considered high mileage for these engines. It runs really well. I was wondering what the difference was between some high mileage brands, and conventional motor oil.

I know the difference between synthetics. They contain detergents. I don't know a whole lot about high mileage vrs conventional however. Is the ideal somewhat like the older motor oils they used to use? In that, they contain particles that help to fill the pocks and dings inside your cylinder heads? I think in the past they used to use a zinc additive in motor oils, too bad those weren't still around.

EDIT: I will be Google'ing this subject, and return shortly for your feedback.

 

A lot of folks use Rotella because it has zinc in it which is better for our 4.0s.

 

High mileage oils generally contain a bit more detergent, and some sort of stop-leak additive. IMHO not worth spending more $$ for.
I've always used ordinary 5W30 Valvoline. 223,000 miles and no problems. DW's Chevy 3.4 is up to 270K on the same diet. Rotella seems to have quite a few good mentions as well.

No motor oil that I'm aware of has particles to fill in worn metal. There are a few oil additives that claim to do that- Restore and it's knock-off's. Whether or not they actually "fill in" anything is subject to debate.
They do work well in some cases to temporarily quiet a noisy motor and/or slow down some types of oil burning. Lesser-quality used car dealers have been onto that trick for years, lol. (if you see empty silver Restore cans in the trash at a prospective used car dealer....you know what he's been up to, lol) It's harmless enough, but it doesn't fix anything either...just covers up the symptoms.

 

Most important, due to the upside-down mounting of our oil filters is to use a quality oil filter with a good anti-drainback valve. Napa Gold and Wix fit the bill. Stay away from orange filters for sure.

 

While Googleing, hope oil myths is read and one will understand that both conventional and synthetic oils contain detergents and other additives.

 

If you really want to pour eons into the subject, visit http://www.bobistheoilguy.com/.

My personal vote is for a diesel oil. Shell Rotella comes in fermentosaurus and synthetic varieties and is a decent price. Here's *why* I say diesel oil:

- The AMC straight-six design is an ancient design that originated in the 60s. Back then roller cams weren't popular (not sure if they were invented TBH, I won't claim to be an expert). Up until the 90s when emissions concerns grew, engine oil had a lot of zinc in it, which protects the flat tappet cams in our engines from wear. This was reduced as when the oil got burnt it accelerates deterioration of the catalyst in catalytic converters. For several reasons diesel oil still maintains high zinc content. This makes it friendly to our flat tappet cams.

- Diesel oil has greater detergent levels and the ability to control soot. In an engine with some buildup and worn rings this is a nice thing to have to control blowby and filth as well as gently work on some cleaning.

- The higher viscosity can be of benefit to some people. In engines with worn bearings it can extend the servicable life before a rebuild is required. Sort of like (the good) additives such as Restore - not meant to be a permanent fix by any means, but can hobble you by. Good advice is to run the viscosity specified by your manufacturer, but as seals wear and clearances get larger than they used it is sometimes recommended to go up a bit. It is absolutely true that running a heavier oil than what is specified by the manufacturer can lead to premature wear, like harder starts, reduced oil pump life, and so on. But, depending on your climate, running thicker oil isn't necessarily a bad thing. For example, in Europe and Australia, the manual specifies 10W- or 15W40. Folks running across the Outback have been known to tun 20W50, even! For colder climates Shell Rotella T6 and Mobil1 TDT are 5W40. Personally, in the winter up here in Ontario my XJ would definitely be in the "severe" service category as there won't be many occasions for it to warm up all the way for my daily commute. In that case when it's -20 I'll probably still run 5W30.

- If you have mean piston slap or a crappy pulley on the front that makes your engine clatter like a diesel, put some diesel oil in and play pretend! The 4.0 has great low-end torque lol

Just my opinion, I'd like to think I put some thought into it. Any feedback is helpful and I hope this helps.

 

I used Valvoline HM oil and it helped sal my rear main seal leak..

 

My opinion also. Rotella and a Wix or Napa Gold filter. Go for it.

 

I can get Rotella relatively cheap where I work. Like $13 for a 5qt, and I already use Wix.

My engine doesn't slap, ping, or knock though... Would this still be recommended?

 

Using an oil with a low or zero 1st number will go a long way toward keeping your motor from slap, ping, or knock. Read Motor 101 over at BITOG.

 

Rotella and Wix go together like peas and carrots. I think Forrest Gump said that........

 

i really like the rotella synblend 10w30 and a wix or napa gold filter. 249k on my xj. getting 18.5mpg and i don't need to add any oil between changes.

take reasonable care of a 4.0 and it will out live a honda.