Fresh engine- what oil? - JeepForum.com
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post #1 of 33 Old 12-13-2019, 08:24 AM Thread Starter
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Fresh engine- what oil?

I got my 4.0 back from the shop and it is all rebuilt. The machinist said to use a dedicated break-in oil with ZDDP first and change it as soon as I was satisfied everything was working properly. Then to use the same type break-in oil for the first 500 miles and then change it again. Then to use a good dino oil for the next 2000 miles. After that I could switch to full synthetic oil. I am scared of ruining this fresh engine by using the wrong oil. I don't want to start a pissing contest over ZDDP content either. This XJ has three Cats and I know ZDDP is bad for them. I noticed these 4.0 engines use single valve springs. That would indicate light spring pressure on the valve train. So maybe ZDDP is not all that important. The factory manual recommends an API certified multi viscosity oil but does not indicate which one. It also says to use an ENERGY CONSERVING oil such as 5W-30 or 10W-30 depending on climate. So can I get some real-world experiences from guys who have broken in fresh engines? What oils did you use for good or bad?

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post #2 of 33 Old 12-13-2019, 11:10 AM
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The Jeep factory just used regular oil when they built your Cherokee. Use whatever viscosity oil is correct for the climate, and add some extra ZDDP, or use a diesel oil. Follow the oil changes changes recommended. Light valve spring pressure and low RPM's do not require large amounts of ZDDP.

Regular oil changes are the most important factor for long engine life, the brand name of oil, or regular vs. synthetic doesn't really matter that much.
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post #3 of 33 Old 12-13-2019, 02:12 PM Thread Starter
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Originally Posted by CJ7-Tim View Post
add some extra ZDDP,
That is my concern. In 2001 they added two cats right under the intake manifold. I don't know how much ZDDP was in the oil back then. Too much ZDDP can harm the Cats and I don't even want to think about replacing three cats because I poisoned them.
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post #4 of 33 Old 12-14-2019, 12:15 AM
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I don't even want to think about replacing three cats because I poisoned them.
You sure don't want the ASPCA to find out about that.

Zinc was used as an additive for breaking-in hydraulic lifters engines, something to do with the amount of force on the camshaft and wear patterns. Modern oils probably use some other additives. But if unsure most people here would probably recommend Rotella which contains zinc (personally never used it). I doubt engine oil that comes right out of the can would damage the cats, you probably would have to add it as a drop-in additive to risk having to much of it.

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post #5 of 33 Old 12-14-2019, 09:14 AM Thread Starter
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Quote:
Originally Posted by CJ7-Tim View Post
The Jeep factory just used regular oil
Regular oil back then still had a lot of zinc. They started taking out the zinc around 2006 so that means five years of zinc oil didn't kill the Cats. maybe I am over-thinking this.
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post #6 of 33 Old 12-14-2019, 09:54 AM
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I use whatever oil is on sale, and a bottle of STP in my 2000.

My 1998 was a fleet vehicle and had about 160,000 miles on it when it bought it. It received regular oil changes with generic bulk oil from a 55 gallon drum. I drove it to 284,000 miles and it used about 1/2 qt of oil between changes, and had excellent oil pressure.

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post #7 of 33 Old 12-14-2019, 06:37 PM Thread Starter
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I have two old pushrod engines that were broken in on zinc rich oil after rebuilds. A Pontiac 301 and a Pontiac 400. After break-in both have been on some old Mobile 1 15W50 that I loaded up on at a discount chain store. That oil still had a good amount of zinc and I have a lot left so those two are safe. No cats on either. It is the 4.0 initial cam break-in I am worried about. I am leaning towards mineral Chevron Supreme 10W40 for break-in oil. If I add ZDDP to it for first fire-up I don't think it will harm the Cats but will protect the metals.
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post #8 of 33 Old 12-15-2019, 12:23 PM
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Corvette comes with a pushrod engine still to this day, including the 2020 model. Overhead cam couldn't possibly fit in it, part of the reason why they kept the small-block configuration. They are factory filled with M1 (what I happen to use on my 4Ls), would be interesting to know if there is a reason for it.

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post #9 of 33 Old 12-15-2019, 12:55 PM Thread Starter
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I too use Mobile 1 in everything. I get the most consistent oil pressure over the life of the oil change. This site https://540ratblog.wordpress.com/ rates the M1 5W30 as one of the best and does mention that OEMs ship with it in there. It is #18 out of almost 300 oils tested for wear resistance and shear. 115,635 psi is in the "INCREDIBLE" zone. I will use it after break-in for sure.
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post #10 of 33 Old 12-15-2019, 01:18 PM
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Quote:
Originally Posted by Fourspeedman View Post
I got my 4.0 back from the shop and it is all rebuilt. The machinist said to use a dedicated break-in oil with ZDDP first and change it as soon as I was satisfied everything was working properly. Then to use the same type break-in oil for the first 500 miles and then change it again. Then to use a good dino oil for the next 2000 miles. After that I could switch to full synthetic oil. I am scared of ruining this fresh engine by using the wrong oil. I don't want to start a pissing contest over ZDDP content either. This XJ has three Cats and I know ZDDP is bad for them. I noticed these 4.0 engines use single valve springs. That would indicate light spring pressure on the valve train. So maybe ZDDP is not all that important. The factory manual recommends an API certified multi viscosity oil but does not indicate which one. It also says to use an ENERGY CONSERVING oil such as 5W-30 or 10W-30 depending on climate. So can I get some real-world experiences from guys who have broken in fresh engines? What oils did you use for good or bad?
Why would you not do as the person that is putting his name on it wants? If you do something different and it calves, is the guarantee void? You are not going to bother the cats with the zinc additive. In some areas where Jeeps are sold 15 w 40 is the recommended oil.

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post #11 of 33 Old 12-15-2019, 02:34 PM
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Back when I got my rebuilt engine I got a lot of conflicting advice. I contacted Jasper, and they did not particularly recommend any additves. I adapted some of what is in this article from Lycoming to my plans (especially, pushing the engine hard at times)

https://www.lycoming.com/content/har...t-engine-break

After an initial run with conventional oil, I switched to Mobil 1 and that's what I've used for the last 120,000 miles.

Regarding zinc, the hype exceeds the reality. Hotrod engines with strong valve springs and aggressive cams have failed during breakin, as well as old British sports cars (probably for similar reasons). While it possibly is a good idea to use zinc additive during break in of a flat tappet engine, it should not be necessary after that. As one tribologist explained: zinc was an early and cheap way to improve primitive oils in the old days. There are better chemistries in modern oils.

One final thought: Just because the Jeep/AM six was designed during the 60s, there is no reason to stick to 60s era lubrication now. You were lucky to have an engine last past 100K back then, now it's normal. Part of that is modern materials, but a very big part of that is modern lubrication.
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post #12 of 33 Old 12-15-2019, 03:13 PM Thread Starter
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Why would you not do as the person that is putting his name on it wants?
Because he advised using break-in oil over-loaded with ZDDP. Some of the oils he suggested even advised "NOT FOR USE WITH CATALYTIC CONVERTERS" . I am not surprised because most of his customers do not run cats at all. I am going to talk to him again before I go ahead. Jay-h- you are correct. Modern oils are light years ahead of the old stuff. I once spoke to an Evinrude engineer. I asked what oil to use in a 1956 30hp outboard engine that originally took a 32 to 1 ratio of 30 wt oil. He told me to use a 50 to 1 ratio of modern TCW-3 oil because the new oils were that much better. The motor loved it.
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post #13 of 33 Old 12-16-2019, 04:23 AM
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How many miles? I'm pushing 270K
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post #14 of 33 Old 12-16-2019, 09:01 AM
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Originally Posted by Fourspeedman View Post
Because he advised using break-in oil over-loaded with ZDDP. Some of the oils he suggested even advised "NOT FOR USE WITH CATALYTIC CONVERTERS" . I am not surprised because most of his customers do not run cats at all. I am going to talk to him again before I go ahead. Jay-h- you are correct. Modern oils are light years ahead of the old stuff. I once spoke to an Evinrude engineer. I asked what oil to use in a 1956 30hp outboard engine that originally took a 32 to 1 ratio of 30 wt oil. He told me to use a 50 to 1 ratio of modern TCW-3 oil because the new oils were that much better. The motor loved it.
This is not what you said in your first post, you said "The machinist said to use a dedicated break-in oil with ZDDP. Common sense would dictate if the oils are "NOT FOR USE WITH CATALYTIC CONVERTERS" then don't use them. Whose definition of "over-loaded with ZDDP" are you using?
Too much ZDDP is not only harmful to your cats but can increase valvetrain wear as well. Break in oil isn't just for protecting valve train wear. The initial use until you are satisfied everything is working properly is good advice. A dedicated break in oil has no friction modifiers and a limited amount of detergents. When should you be satisfied everything is working properly? 20 minutes? . Change the oil and filter, (cut open the filter and see how much grunge is in there) and refill with whatever you are comfortable with, If you think 20 minutes was all it needed, great, use what you want, if not use the break in oil for a while longer. It is your engine after all.

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post #15 of 33 Old 12-18-2019, 09:40 PM
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You need to break it in before using synthetics. Those parts need to get comfortable with each other BEFORE you give them the ultimate lube. What that is for an AMC 258/Jeep 4.0 is debatable.

Back in the day (1986) the AMC dealer wanted the new Jeep back after 7,500 miles to change the oil and restricted you to 55mph for the first 500 miles. I cannot believe this was using a break-in oil, however it was undoubtedly a mineral oil.

My Jaguar V12 had a break in oil for 1000 miles, then the dealer swapped it for a synthetic oil. I have been lumbered with this oil ever since, the engine barely puts out 55bhp per litre and is quite capable of running on oil half the price. It still holds 75psi when warm after 30 years though, with no engine work.

Your supplier's advice seems fine. I would suggest an oil which does not say "not for use with catalytic converters"

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