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Discussion Starter #1
So I have a 1989 yj with a 4.2l engine, ax-15 tranny, and np231j t-case that I have been putting 10w-30 full synthetic in for the last 5-6 years. My friend told me that it is bad to put motor oil in my transmission and t-case, is this true? Any one else care to share what fluids you use in your rig.
 

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So I have a 1989 yj with a 4.2l engine, ax-15 tranny, and np231j t-case that I have been putting 10w-30 full synthetic in for the last 5-6 years. My friend told me that it is bad to put motor oil in my transmission and t-case, is this true? Any one else care to share what fluids you use in your rig.
Transfer Case takes ATF.

Transmission - 80w/90 gear oil (GL3)

Engine should use a oil with zinc.....DELO or Rotella in a 30, 40 or 15w/40 depending on temperature. The zinc is very important for your flat tappet cam in the 258.

These are factory fluids and I'm a firm believer in not trying to outsmart the engineers who designed the Jeep.
 

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Transfer: ATF +4
AX15: Red Line MT90
Engine: Royal Purple 5W 30
 

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Let me clarify... I'm in the NorthEast. 5w 30 in the winter. 10w 30 normally.


I'm sure that 10w 30 would be fine all year.
 

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Discussion Starter #5
I used atf +4 for a while in my t-case but didn't like how bad it worked, and same with the 75w-90 fluid in the tranny. The tranny fluid just didn't do good where I live because of temperature (Southern California kept my tranny VERY hot)/ destroyed syncros, but the 10w-30 keeps my tranny cool and made shifting smoother. And the atf +4 kept eating up my output shaft seals on my t-case.
 

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In my 89 4.2 I use full syn. 75W90 gear oil in my Ax15 trans. and diffs., 10W30 in my engine and ATF in my transfer case. You can use full syn 10W30 in your trans. without any problems, but I would only use ATF/ATF+4 in the transfer case.
 

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Discussion Starter #8
In my 89 4.2 I use full syn. 75W90 gear oil in my Ax15 trans. and diffs., 10W30 in my engine and ATF in my transfer case. You can use full syn 10W30 in your trans. without any problems, but I would only use ATF/ATF+4 in the transfer case.
I'll go back to using atf in my transfer case then, but can anyone name a brand that won't eat through my seals every 2 months.
 

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I'll go back to using atf in my transfer case then, but can anyone name a brand that won't eat through my seals every 2 months.
ATF shouldn't eat seals. They're designed for it. You may have a balance issue or something. Use a high mileage ATF, it has ester additives that swell seals to prevent leaks. Stay away from synthetics if you have leaks, they have better flow characteristics and will find the weak spots in seals and flow out faster than conventional ATF.
 

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I run ATF in the t-case and trany but I got an auto. As far as the 4.2 I use to use castrol 10w 30 and castrol is what I run in every thing but my diesel and love it but I had some lifters that were starting to tap pretty bad so I changed the oil and put in rotella 15w40 and less than 5 min after I cranked it after the oil change the lifters quit tapping so I been using it ever since.
 

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image-2222341696.jpg

I just put a new motor in my jeep, 4.2l, and this is from the builder. Make sure whatever oil you use has zinc!! I've heard the Valvoline racing oil has zinc.
 

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Mbclark I think the distinction is that this is a newer engine and the builder is saying use a zinc based oil.

Newer engines are made primarily from recycled metal and the amount of Zinc in the engine is less than years ago when engines were made with new metal and this had more zinc in them.

Or so I remember.

Not sure how or why I remember this so if it seems like bs it could be.
 

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Mbclark I think the distinction is that this is a newer engine and the builder is saying use a zinc based oil.

Newer engines are made primarily from recycled metal and the amount of Zinc in the engine is less than years ago when engines were made with new metal and this had more zinc in them.

Or so I remember.

Not sure how or why I remember this so if it seems like bs it could be.
Makes sense and is very possible. The way I look at it is what can it hurt? Most oils I've found with zinc are diesel oils, which are rated by SAE as "C" or commercial oils for Diesel engines and "S" service station or gasoline engines so your safe either way.

I also know that it common for manufactures to back date fluid recommendations when they develop a new or superior product. Usually because a system or component commonly has failures and the new product helps to prevent or prolong those failures. GM did it recently with the introduction of Dexron VI ATF. They put out a TSB and backdated all the old Dexron III vehicles to the Dexron VI application. Makes it confusing as hell for us people in the auto repair/maintenance industry. Keeps us on our toes!!!!

You got me very interested as to why exactly my builder is recommending that additive. Time for some research.....
 

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Agree 100% what can it hurt


As far as engineers being right about what type fluids engineers design based on general atmospheric conditions so if your jeep runs good in mountains on a thinner oil use it not sure who made the engineer comment not saying you did mbclark
 

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Agree 100% what can it hurt

As far as engineers being right about what type fluids engineers design based on general atmospheric conditions so if your jeep runs good in mountains on a thinner oil use it not sure who made the engineer comment not saying you did mbclark
That was me, it was more referring to type of fluid....ATF, GL, etc....

I'll agree with the oil viscosity....to many variables contribute to proper viscosity to make a blanket rec.
 
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