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Discussion Starter #1
all these question are for my 92 yj 4.0. stick shift

Recommended oil for engine?

What type of Transmission fluid?

normal operating temp. of engine?

Also what are the signs of a lean fuel mixture?

Thanks in advance
 

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Oil: I personally like 10w30 rotella T5, has good detergents and additives even for flat tappet cam motors.

Trans fluid is a loaded question, but as a transmission builder/gear guy I will recommend redline MT90, but any yellow metal safe 75w90 gear oil will work.

Normal operating temp is controlled by the thermostat which I think stock is either 192 or 195 fahrenheit, someone else probably knows which better since I don't have a jeep engine anymore.

Lean fuel would be shown by the spark plugs, if you think you're running lean, a fuel pressure test is never a bad idea but sometimes it is fixed with a new fuel filter or O2 sensor if either are past their mileage service range:
 

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Discussion Starter #3
What are peoples thoughts when chosing new spark plugs? Will any new plug be fine? Or is a a certain type known to work best with the 4.0 engines?
 

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Cheap Champion copper core plugs. The exotic multi-tip expensive plugs are a waste of money and don't work as well as the less expensive plugs.

Champion FN 14LY
OR
Champion RFN 14LY

Good Luck, L.M.
 
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As for transmission lubricants Chrysler and Aisin (the manufacture) recommend GL4 yellow safe gear oil or 10w-30 Full synthetic engine oil. Redline mt90 is good stuff that will cost $70 a gallon. 5 quarts of Full synthetic will be $30 or less... Your choice


Transfer case takes Mercon Auto trans fluid.


Any brand of 10w-30 engine oil is what's recommended by Chrysler. I prefer Castrol GTX


Diffs take something like 75w-90 or 75w-140 for heavy use (towing)
 

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Discussion Starter #6
As far as spark plugs are concerned what is the gap on them in the 4.0 ky jeep us a 92 if that changes anything. I looked around online mostly saw .035 is this the correct gaping?
 

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.035 is correct
 

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As for transmission lubricants Chrysler and Aisin (the manufacture) recommend GL4 yellow safe gear oil or 10w-30 Full synthetic engine oil. Redline mt90 is good stuff that will cost $70 a gallon. 5 quarts of Full synthetic will be $30 or less... Your choice


Transfer case takes Mercon Auto trans fluid.


Any brand of 10w-30 engine oil is what's recommended by Chrysler. I prefer Castrol GTX


Diffs take something like 75w-90 or 75w-140 for heavy use (towing)
10w30 is a bad suggestion for anything other than the nv3500 or nv3550. I and other transmission rebuilders have found many problems in transmissions that had 10w-30 put through them. Basically all the thrust surfaces are overworn and the gears that ride against the thrust surfaces are worn. Aisin never recommended 10w30, and no other auto manufacturer (toyota and gm) who uses variations of these transmissions (AN5s, AR5s, MA5s, and r154s) recommends 10w30. I and other actual transmission rebuilders will only recommend 75w90 yellow metal safe gear oil.
 

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10w30 is a bad suggestion for anything other than the nv3500 or nv3550. I and other transmission rebuilders have found many problems in transmissions that had 10w-30 put through them. Basically all the thrust surfaces are overworn and the gears that ride against the thrust surfaces are worn. Aisin never recommended 10w30, and no other auto manufacturer (toyota and gm) who uses variations of these transmissions (AN5s, AR5s, MA5s, and r154s) recommends 10w30. I and other actual transmission rebuilders will only recommend 75w90 yellow metal safe gear oil.
That's funny, so many folks run and suggest including Chrysler and Aisin to use 10w-30 in an Aisin AX5/15 transmission. If you look in the FSM supplements you can read it with your own eyes or maybe call your local Jeep dealer and ask them.
Seeing how you say you are an "actual" transmission re-builder you would think you would be up on the Manufacture service supplements.

SocalYJ805 Google it there is a wealth of info on the subject

https://www.google.com/search?client=firefox-b-1-d&biw=1366&bih=631&ei=oZksXrmdJovJtQaH8IvoCw&q=ax15+10w30+synthetic&oq=ax15+10w30&gs_l=psy-ab.1.1.0j0i30.0.0..184232...1.0..0.118.118.0j1......0......gws-wiz.MbDnlcGZ1Q8


https://www.google.com/search?client=firefox-b-1-d&ei=DJssXrT0H_iF9PwPxOGaMA&q=recommended+oil+for+ax5%2F15&oq=recommended+oil+for+ax5%2F15&gs_l=psy-ab.3...6761.58983..60903...0.0..0.210.7144.0j55j1......23....1..gws-wiz.......33i160.iTyENIzNKdA&ved=0ahUKEwi0qu-Gwp_nAhX4Ap0JHcSwBgYQ4dUDCAo&uact=5


Just wish I could find the actual Service Supplement for you it's out there somewhere
 

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That's funny, so many folks run and suggest including Chrysler and Aisin to use 10w-30 in an Aisin AX5/15 transmission. If you look in the FSM supplements you can read it with your own eyes or maybe call your local Jeep dealer and ask them.
Seeing how you say you are an "actual" transmission re-builder you would think you would be up on the Manufacture service supplements.

SocalYJ805 Google it there is a wealth of info on the subject

https://www.google.com/search?client=firefox-b-1-d&biw=1366&bih=631&ei=oZksXrmdJovJtQaH8IvoCw&q=ax15+10w30+synthetic&oq=ax15+10w30&gs_l=psy-ab.1.1.0j0i30.0.0..184232...1.0..0.118.118.0j1......0......gws-wiz.MbDnlcGZ1Q8


https://www.google.com/search?client=firefox-b-1-d&ei=DJssXrT0H_iF9PwPxOGaMA&q=recommended+oil+for+ax5%2F15&oq=recommended+oil+for+ax5%2F15&gs_l=psy-ab.3...6761.58983..60903...0.0..0.210.7144.0j55j1......23....1..gws-wiz.......33i160.iTyENIzNKdA&ved=0ahUKEwi0qu-Gwp_nAhX4Ap0JHcSwBgYQ4dUDCAo&uact=5


Just wish I could find the actual Service Supplement for you it's out there somewhere
I recommended 10w30 for ax15 transmissions for a few years because of the mopar recommendation(you can easily find old threads on this forum where I recommended it), but after getting a good amount of the ones I rebuilt back for warranty repair that had 10w30 in them, they all had downshifting issues and the thrust surfaces were all severely worn meaning I had to pay out of pocket for hard parts like output shafts and gears. I don't care what Chrysler recommends as I've seen otherwise. Engine oil does not have extreme pressure additives for proper longevity of hard parts.
 
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Well I'll tell you this, I've been running full synthetic 10w-30 in my TJ for 6 years and pretty sure that's what I drained out of it when I bought it. Also run it in my YJ for a year now, It had gear oil in it when I bought it. I change the oil in both once a year (could go longer) along with all the other fluids during my spring tune up sessions. Never any problems, trannys shift smooth, no problems shifting up or down, and run quiet.
 

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Well I'll tell you this, I've been running full synthetic 10w-30 in my TJ for 6 years and pretty sure that's what I drained out of it when I bought it. Also run it in my YJ for a year now, It had gear oil in it when I bought it. I change the oil in both once a year (could go longer) along with all the other fluids during my spring tune up sessions. Never any problems, trannys shift smooth, no problems shifting up or down, and run quiet.
maybe changing the fluid often helps as motor oil is known for shearing. Still, I'll recommend gear oil that can run in the transmission without change for its service life as long as you don't get water in the trans.
 
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