I was planning on flushing and replacing my automatic transmission fluid in my 1999 XJ (just under 120k) that I recently bought, but when I went to my local auto parts store for some Dexron, the salesman advised me not to. He said something to the effect of "Changing the thickness of the fluid could cause your gears to grind up because higher mileage transmissions (over 100k) get used to the fluid currently in it."

Does this sound right? I've just recently started educating myself on engines and transmissions, so that I can keep my XJ running like new. But I'm no mechanic, by any means. Any of you veteran grease monkeys out there have an opinion on this?

Thanks for the help!

 

I recently just changed out my torque converter, my friend said do NOT change the fluid, just add, like your parts guy said, they do get used to the fluid.

 

You should change it. What he was probably referring to. Is not to flush it. Like any oil the trans fluid will break down. What you should do is just drain the trans from the oil pan and refill it. Do this several times until the trans fluid is nice and red as it should be then replace the filter and you will be good to go.

 

Nope. Sounds like he's been smoking something he shouldn't.

If you bought a vehicle, and the engine oil hadn't been changed in a long time, would you just keep driving it forever on the old oil? Neither would I.

Buy some decent quality Dex/Merc (Dex III) and drain the ATF using the drain plug on the pan. Super easy. Add new fluid, then drive it for a week or so. Repeat maybe three more times, and a good majority of the fluid will have been changed.

 

It all depends on fluid color if its red like new fluid you should be ok if its burnt and brown youve got about 50/50 chance of tranny issue arising . Being brown you can change filter and reuse brown fluid top off with new fluid.

 

Multiple drain and fills with D/M is the best way to go. The transmission itself holds around 4 quarts of ATF, whereas the entire system capacity is around 8. 120k is barely broken in on these things, but if you're paranoid you can drain just a small amount at a time. However would be very prudent to drop then pan and take a look inside. May be some surprises waiting for you in the filter.

Regular fluid changes are essential to longevity in anything on your Jeep. Leave it and it's guaranteed to die as the oil continues to be sheared, burnt, and loses most of its desirable properties. It's kind of like never changing your underwear because clean stuff chafes.

There CAN be an issue if the old ATF has so much clutch material suspended in it that your transmission won't work right with clean fluid. You could add some old stuff back in temporarily, but that means you need new clutches.

 

I just drained 4 quarts and added 4 quarts, Then repeat the next month.
It just depends how it looks, If it is brown then do that and after about 3 times it will be new fluid.

 

I agree with belvedere.

Drain the pan fluid multiple times (with some driving inbetween) until the fluid stays red in color. At that point, I would consider dropping the pan and changing the filter.

 

Just changed mine not to long ago... Just drop the pan and change the filter...
Don't flush the system. That's when problems occur...

 

Do you need a new gasket each time you drop the pan?
Or do you use RTV ?

 

With 120k mile, I would just do a couple of drain & fills within short intervals - like 3000 miles and be done with it. And don't forget the transfer case. Its probably neglected as well.

 

DO NOT drop the pan. The "filter" is just a screen. Drain and refill with about 3.8 quarts of Dex/Merc and call it good.

If YOU dropped the pan, we'd have 3 threads of about 76 posts each with you *****ing about how only professionals can work on Jeeps. Here's your chance to do something simple and successfully. Go for it.

 

Drop the pan, and wipe up the gunk on the bottom, pretty sure the filter is a paper material when I did mine.

Doing both of those will reduce contamination of new fluid added...

 

Unfortunately I have to drop the pan on mine... It's leaking from around it.. But like cruiser said.. There really is no point in dropping the pan unless you have a leak or you really need to get in there.

Do you drop the oil pan and clean the sump screen when you change your oil? Lol save yourself the headache.

 

Drain and fill. Drive repeat. As has been said above.

Dropping the pan isn't all that bad if you've ever taken one off before and know some tricks. If you've never taken one off then have someone who's done it before help you.