Bought a project vehicle but previous owner only had it for a little bit and never did work on the tranny. He doesn't know what trans fluid was used previouisly and I'd like to drain and refill since the fluid is pretty dirty/dark. I want to make sure to put the right one in and not mix since I know that'll cause issues. Any idea how to actually tell the difference from the fluid I have in my xj now?

 

All Jeep Cherokee trannys take dexron 3. A plain drain and refil takes a bit more than 3/4 of a gallon. Fill it with that much then take it for a spin to get proper full level

 

1) there's no way to tell what's in there now. If you're worried about it/it looks dark or dirty and you want to "change" it ....

Do this
2) the drain and fill mentioned above drains the pan, but the total fluid capacity of the transmission with torque converter is about 8 quarts. If you really want to change what's in there you need to do the pan drain, drive it a bit, and repeat a few times. What you're doing is diluting the old fluid with new fluid.

 

You're fine mixing in Dex3 if there is ATF4+ in there.