Advice needed...lubricants

Purchased my first jeep on saturday. No knowledge on service history so I want to change all the fluids( will have to be one at a time for budget reasons).

It's a 95 SE 4.0L.

Have the oil filter ordered (PL30001).

Looking for the best detergent oil for the engine. Where I live; it is almost -30 tonight. I grew up in Florida; and used Shell RotellaT 15w-40 in winter and Valvoline VR1 20-50 in summer. Occasionally used Mobil1 to clean out a new used car or truck. Wondering what oil will best clean out the engine?

My usual combo for cleaning would be 4 parts oil and 1 part marvel mystery oil or seafoam and a new top end filter for 1-2 weeks then switch back to regular oil...

Second step will be differential....Again temperature range from -45 to 90 degrees...what would be best oil?

This may be a dumb question but I am guessing that the front and rear differentials and transfer case all use the same lubricants and should/need to all be changed at the same time? Or is the transfer case filled with a different fluid like tranny fluid?

90W for the diffs and ATF for the tcase

Yep, atf for the t-case and you can what to change it. Personally i would do it with the transmission because you will be buying the fluid then and the t-case only holds a quart (if i remember correctly), so you will probably have that left over from the trans. On the transmission be sure to go with Dexron III or one that is compatible with Dexron III, don't believe the hype about ATF+4. Also, since this vehicle is new to you its probably best to drop the pan and change the filter too.

75w-90 is a very common gear oil for the diffs and what the factory put in them.

On the motor oil, i personally run 5w-30 castrol gtx in the winter but we get no where near as cold as you have so i am probably not the best judge on that.

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