Ok so gunna change and check my oil levels In my cherokee I have the renix 4.0 with a 5 speed 4x4 so question is what oils should go where. I live in so cal. So is a 10/30 ok for the motor oil what fluids go in the manual trans ? ATF or gear oil? If ATF is Rex merc ok? If gear oil 80-100 ok ? Transfer case same question. And axles are obviously gear oil.

 

Do not use ATF in a manual transmission. It is best to use a GL3/GL4 spec gear oil. Regular gear oil (GL5) degrades the synchros in the transmission because of the sulfur content. GL3/4 oils have less sulfur. I have had good luck with Redline MT-90 oil in my transmission.

I live in Canada, so I have a lot different experience with engine oil than you probably do, but I think that 10w-30 or 10w-40 would be an appropriate weight.

For the differential oil, it depends on whether you tow or not. If you tow, the Factory Service Manual recommends 85w-140 gear oil in the rear differential. For the front, and/or if you do not tow, in the rear, 75-90 is recommended. Also, if you Jeep has a limited slip rear diff, you are supposed to put a bottle of friction additive for the LSD in with the gear oil. It is probably available where you buy your other fluids, but if not, the dealer has it available.

For your Xfer case, dex-III or dex IV ATF are both good.

 

Ok cuz at work I have Rex merc and 80-100 synthetic gear oil on tap and 15-40 motor oil so I should be able to rock all that good free stuff

 

80-100 Gear oil for the diffs sounds like a plan to me... Plus you won't be stealing much, I think its only like 1.3 qts for each diff. And I have no idea what the temperature is like in so-cal this time of year, and that is a very influential factor when choosing oil weight.

Edit: I just checked the service manual, it pretty much says that if your temperatures never (or very rarely) go below freezing, the 15-40 would be a good choice.

 

+1 what EvstaG is saying. Especially about the transmission. Pennzoil and Castrol have "Synchromesh" products that work well, otherwise Redline MT-90 or Royal Purple gear oil (API GL-5 rating but doesn't use a heavy sulphur EP additive) is what brass synchro trannies need these days.

Also fun fact: the NP231 will take ATF+4 too