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Discussion Starter · #1 ·
Hi
My daughter’s recently acquired 08 has 208000 km (130000 miles). No idea if any of the fluids have been changed. I know it’s had some off road use.

The fluids all are topped up and look clean but does that mean much?

Should they all be changed to be safe?

What would you use?

Thanks for the help.
 

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Auto trans fluid change interval is 60K miles if towing, 120K miles normal duty. (Not sure what the interval is for manual trans.) In the case of an auto trans, I would definitely perform the service as neglecting ATF changes kills transmissions. Even worse, for '08 we got a crappy trans cooler that doesn't work very well, so the ATF suffers extra heat damage. Even if the fluid was changed, there's no harm in changing it again: a normal fluid change replaces maybe half (only the stuff in the actual trans gets drained, the torque converter stays filled with old). I don't recommend the "fluid exchange" procedure where they hook up to the cooler lines and pump in fresh ATF as old ATF is pumped out; this leaves a dirty filter screen and all the gunk in the trans pan. Not good.


I would also do at least the rear diff fluid, there's a thread here about a clunk in the back end that seems to be caused by broken/chipped teeth in the rear diff. So it's something you don't wanna neglect, diff oil is a cheap investment compared to a new ring and pinion. I'd use synthetic here.

Not sure about the transfer-case or front diff maintenance interval, though. I'm still a Jeep newbie so curious to hear what others think.
 

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When I get a used vehicle I like to change all the fluids that way I know what’s been done and can start new. As to interval you are going to get a lot of opinions I’ve always had good luck just doing the severe service intervals in the manuals. :bop:
 
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Discussion Starter · #4 ·
Thanks. I’ll change it all out.

I was reading about the fluid being left behind in the tranny. Is there any way to get this out? Mixing old with new doesn’t seems silly.

I didn’t realize the tranny cooler wasn’t the best. It’s part of the AC condenser, isn’t it? I just replaced this. Hopefully it’s better than stock? Or will it still be not so good? Does the tranny only get hot off road / towing?
 

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Discussion Starter · #5 ·
I happened to be in a dealership today so I asked if there was a way to get all tranny fluid out when changing the pan. He said a flush would but the pan stays on so the filter doesn’t get changed. He also said he wouldn’t recommend flushing an older tranny as this can get rid of the particles that are “holding it together”. Really? Sludge and such keeping a tranny going - surely that has to be an exaggeration except in some weird case where it’s about to give out anyways.

Any brands of synthetic fluids better than others?
 

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If the fluid is not too bad I would just drop the trans pan,replace filter and go on. Personally not a fan of flushes. If you have done trans services you will find sludge,and debris in the pan some have magnets to catch metal in them. Wouldn’t want that stuff being forced through my trans. Also just use the recommended oil. Trans cooler is not part of the ac condenser totally different system. Not sure about yours but usually part of radiator. Unless you have a remote one.
 

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Discussion Starter · #7 ·
I can see not wanting to push crap back up into the tranny.

Surely synthetic fluid breaks down at some point. Why do we add good fluid to bad?

Can you take the pan off and then flush out the rest?
 

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When I get a used vehicle I like to change all the fluids that way I know what’s been done and can start new.
^ this.

I’ve always had good luck just doing the severe service intervals in the manuals.
^ also this. Oil is cheap, metal is expensive.


Mopar ATF+4 in the transfer case. Takes 2.1 qt.

Any good gear oil, 80W-90 API GL-5 in the diffs, 1.35 qt in front, 2.375 qt in rear. Check manual to see if she has a LSD in which case friction additives may be required. Synthetic in rear if towing.

Those are both easy DIY projects if you want to save money.

Can't comment on the transmission, as I drive manual. But I would have it done if I were you.
 

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The trans cooler is different for early and late JKs. On ours, it's part of the A/C condenser and it's tucked behind the bumper so it doesn't get much air. Jeep put a better (separate) cooler on later models, but for those of us with the 3.8L/4spd an auxiliary cooler will help prevent "HOTOIL" messages on the dash when towing or climbing sand dunes in 4H (ask how I know ;) ).


A full fluid replacement generally isn't necessary (or rather, the chemistry of a partial change is factored in to the service interval) because the new fluid brings with it enough detergents and additives to bring the remaining old fluid back into specification, and because the partial change removes "enough" of the contaminants (because the worst of the contaminants are in the filter and pan).



As for changing the ATF on a high-mileage trans, well, here's one of those great internet debates. As clutches and bands wear, the friction material they shed floats around in the ATF and makes the fluid more "grippy" than "slippery". That's no good for the gears (they need lube!), nor for the solenoids and hydraulic passages that tend to get clogged with this debris. So, yes, you will find anecdotal evidence that doing a fluid service on a high-mileage trans can result in trans failure -- and the theory is doing a full flush can increase this risk (by removing all of the suspended friction material instead of just most of it). Either way, if you change the fluid (partial OR full) and the trans quits working, your transmission was already worn beyond limits before you messed with the fluid. The dirty fluid was just hiding the problem.



I got bit by this in my previous car ('03 Olds Alero). Did the normal ATF change (pan + filter, not flush) and the trans started slipping in first gear if you stomped on the accelerator from a stop (this car started life as a rental, so, I think somebody did a lot of neutral-drive burnouts). No regrets though, I still think doing the ATF service was the right choice -- if I'd done nothing, that nasty fluid probably would have caused some other failure and left me stranded some day.
 

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Discussion Starter · #10 ·
Thanks - If the fluid looks good, I won't bother trying to flush it all out. Is the "recommended" change for the next time sooner than the first? - as you are now dealing with fluid that is only 1/2 new and 1/2 rehabbed?
 

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Nope. Had a f150 with 250,000 miles just dropped the pan regularly (30,000miles) and changed the filter. Oil was in good shape when I sold it and no trans problems. Not sure what interval your year calls for. Should be on your owners manual.
 
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