Which tranny fluid and gear oil?

I need to do a complete fluid change in my '99 XJ, but the only manual I have is vague about what specific fluids to use. Does an XJ auto tranny use Dexron III? Also, what about the gear oil for a locking differential? Just regular 80-90W lube? And do I need a friction modifier? Please no expensive "wonder lubes", I just need to know what factory-spec fluids to use. Thanks in advance.

80w-90, with a friction additive for LSD.
If you tow alot, they recommend 75w-140 synthetic.

Dex III for trans/tcase.

99 XJ auto is an Aisin Warner AW4--Dex III.

Regular gear oil, 75-90, 80-90 would work, if towing might consider synthetic and heavier weight. You only need the friction modifier for an LSD--limited slip differential. If that is what you have, then yes you NEED it.

EDIT: damn, defiance665 beat me to it.

I picked up a 5 gallon drum of 80W-90 Coastal Gear oil for just over $40 at Advance like 2 years ago. If your wheeling alot in the mud/water, its really not what you put in the diffs, it how often you change em.

As for the tranny I was about to flush mine and get the pricy Royal purple. met a guy wheeling this weekend and he said he burnt his tranny fluid (like I did) replaced it with RP and hasnt had a problem overheating since.

If its a DD, I would stay away from the low buck ATF, im no expert, but basically the cheaper the ATF, the faster it breaks down and needs to be replaced. If ya really want factory spec, call MOPAR.

Bzamora said:

I need to do a complete fluid change in my '99 XJ, but the only manual I have is vague about what specific fluids to use. Does an XJ auto tranny use Dexron III? Also, what about the gear oil for a locking differential? Just regular 80-90W lube? And do I need a friction modifier? Please no expensive "wonder lubes", I just need to know what factory-spec fluids to use. Thanks in advance.

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If it has a real locker, not a limited slip factory device, but a real locker, no modifier is needed. If it is a limited slip yes, modifier is needed. The transfer case, use Mobil-1 ATF. The first time I changed from factory fluid to mobil 1 atf in the transfer case it cooled it right down. Made shifting smoother, dramatic change. Engine, mobil-1 engine oil, 10W30 'HIGH MILEAGE' green bottle, that has the higher zddp levels in it for our engines or add a bottle of Red stp additive. Guys here have burned out the AW4 with synthetic atf so go with what is recommended here. Walmart has 5 quart Mobil-1 oil for about $24 a jug, I have 4 jeeps so I usually pick up 8 to 10 jugs a year for them.

If you are stepping into the world of synthetics.. I recommend 75w-110 in the diffs frt/rear. Amsoil Universal ATF in the t-case and transmission. A lot say not to use full syn in the AW4, but it has done me just fine.
Also recommend Amsoil "AMO" in your engine its 10w-40 with zddp addative.

Depending on the LSD, if you use the Amsoil full syn you do not need to use the friction modifier. Same with some other full syn. lubricants.

Really, people say no synthetics in the AW-4? talked to 2 guys at Rausch creek who recomended it, and one of them didnt even have a tranny cooler.

Bzamora said:

Also, what about the gear oil for a locking differential?

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Define,XJ's never came with one!

austinaubinoe said:

Really, people say no synthetics in the AW-4? talked to 2 guys at Rausch creek who recomended it, and one of them didnt even have a tranny cooler.

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I think it has a lot to do with how it was maintained, I don't know for sure but most syn's are high detergent so putting in syn in a high mileage tranny that has not had the 20K transmission flushes might be the reason they burn up.
I just had the tranny replaced in our 97ZJ last week, it has 170,000 mi on it, we bought it at around 100,000, there were metal bits in the pan. The tranny that went in is a Jasper performance tranny with a 3yr/100K warranty.
We will be having that tranny flushed their recommended 20K miles for sure, they are not cheap.

I've never really had a problem with synthetic fluids in automatic transmissions--as long as it is the CORRECT synthetic fluid, fully compatible with the original specified fluid. I don't like mixing synthetic with dino, so a flush and fill is the way to go for a changeover.

I agree with the others, a poorly maintained transmission will likely have more problems than one that received proper servicing, the same for a transmission that wasn't abused--overheated, towing MAX loads, etc.

Thanks for the replies. This isn't an off-roader, it's a daily commuter. It's just been a long, long time since any of the fluids outside of the engine oil have been changed.

RichP said:

I think it has a lot to do with how it was maintained, I don't know for sure but most syn's are high detergent so putting in syn in a high mileage tranny that has not had the 20K transmission flushes might be the reason they burn up.
I just had the tranny replaced in our 97ZJ last week, it has 170,000 mi on it, we bought it at around 100,000, there were metal bits in the pan. The tranny that went in is a Jasper performance tranny with a 3yr/100K warranty.
We will be having that tranny flushed their recommended 20K miles for sure, they are not cheap.

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this makes me want to save all the Royal Purple I just bought and run my tranny till it dies. It does have about 160k on it. I may just keep putting the cheaper stuff in it for a couple thousand miles and see how it goes.

How much did you pay for the jasper auto? probably would be hard to find a low miles AW4 in the junkyard though.

oh and I can totally understand the lack of fluid changes in your commuter jeep. my friend has a 94 grand that he picked up from an old lady with 200k highway miles. the tranny was slipping so we pulled the pan and the fluid was very old... i wonder if a tranny could go 200k without a single flush???
oh and the diff's still had there original gaskets!

RichP said:

I think it has a lot to do with how it was maintained, I don't know for sure but most syn's are high detergent so putting in syn in a high mileage tranny that has not had the 20K transmission flushes might be the reason they burn up.

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I've had this experience as well. My first XJ, a 91 with the 4.0 AW4 hadn't been maintained at all, but the PO changed all the fluids shortly before I bought it. The tranny had shifting issues when it was cold, but that went away after draining a couple litres of tranny fluid and replacing it with Lucas goo. Mostly went away that is.

One question I still have; is there any way to tell if the tranny has been neglected before changing the fluid & finding out the hard way? I can't think of a way other than dropping the tranny pan and checking the insides; but then it's pretty much too late unless you re-use your old fluid.

I want to change the fluid on my 92 XJ's AW4, but I'm afraid of causing problems that I can't afford to fix...

austinaubinoe said:

this makes me want to save all the Royal Purple I just bought and run my tranny till it dies. It does have about 160k on it. I may just keep putting the cheaper stuff in it for a couple thousand miles and see how it goes.

How much did you pay for the jasper auto? probably would be hard to find a low miles AW4 in the junkyard though.

oh and I can totally understand the lack of fluid changes in your commuter jeep. my friend has a 94 grand that he picked up from an old lady with 200k highway miles. the tranny was slipping so we pulled the pan and the fluid was very old... i wonder if a tranny could go 200k without a single flush???
oh and the diff's still had there original gaskets!

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The Jasper, about $2200 w/warranty. The 97ZJ still looks new inside and out so we plan on keeping it a while.

XJPhoenix said:

One question I still have; is there any way to tell if the tranny has been neglected before changing the fluid & finding out the hard way? I can't think of a way other than dropping the tranny pan and checking the insides; but then it's pretty much too late unless you re-use your old fluid.

I want to change the fluid on my 92 XJ's AW4, but I'm afraid of causing problems that I can't afford to fix...

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Not really.

Look, you will do MORE damage to the transmission by NOT CHANGING the fluid. If you are concerned, then do a poor man's flush with standard DINO Dex III and don't put in a synthetic. If everything is fine (and it should be) then in 20k miles decide if you want to do another standard or synthetic flush. Again, NOT CHANGING THE FLUID is what will damage the transmission.

That makes sense.

Thanks.

joe_peters said:

Not really.

Look, you will do MORE damage to the transmission by NOT CHANGING the fluid. If you are concerned, then do a poor man's flush with standard DINO Dex III and don't put in a synthetic. If everything is fine (and it should be) then in 20k miles decide if you want to do another standard or synthetic flush. Again, NOT CHANGING THE FLUID is what will damage the transmission.

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Yeah thats what im gonna do. Stash the Royal Purple away in a secret location until i put on a couple thousand for miles on some clean cheap stuff.

BTW It took me a sec to understand what Dino meant. I thought your were talking about one of those machines that that tells you how many HP you have under your hood hahahahah

Yeah, I use dino a bunch because I are one--well, not yet extinct but closing in on it!

joe_peters said:

I've never really had a problem with synthetic fluids in automatic transmissions--as long as it is the CORRECT synthetic fluid, fully compatible with the original specified fluid. I don't like mixing synthetic with dino, so a flush and fill is the way to go for a changeover.

I agree with the others, a poorly maintained transmission will likely have more problems than one that received proper servicing, the same for a transmission that wasn't abused--overheated, towing MAX loads, etc.

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Agreed. I don't care if I mix syn and dino oil though, I figure it's still better than whatever goop was in there beforehand.

I've been running Valvoline MaxLife Dex/Merc (a semi synthetic blend iirc) in my MJ with 200k+ on the transmission since last November or so. Did a drain and fill while replacing the cooler lines. Hasn't killed it yet, and I have a habit of leaving about a thousand pounds of cargo in the back for weeks/months at a time while daily driving it. I'm a fan of the skinny pedal and it regularly sees 85mph under these kinds of conditions. I'm pretty sure I was the first person to EVER change the transmission fluid, it was purchased from the previous owner with an "oil leak" that turned out to be a pinhole leak in the side of the cooler line shooting a stream of ATF onto the side of the oil pan. The ATF was so dirty it looked like very, VERY overdue motor oil and I thought it was till I got some between my fingers.

The AW-4 is bulletproof so long as you don't overheat it and don't put the wrong fluid in it, IMO.

On the other hand the one in my XJ was sorta slipping when I got it, it's currently all kinds of screwed up, not sure if it's an electrical or hydraulic failure but it feels like both. Only has ~140k on it.