Are rear diff service and trans fluid exchange both easy for a beginner?

[Bmnorm2]

Differentials are easy. Any brand fluid will do.

Transfer case is easy, the Toyota fluid is really expensive and a substitute 75W is difficult to find. I don't know if it matters, but the two fluids I found that are compatible are Royal Purple Synchromax and RAVENOL J1C1003 MTF-3 SAE 75W Full Synthetic Gear Oil. There's a possibility of some brass gears that normal gear lube may not be compatible with, I didn't have a problem when I used 75W-90, but I prefer not to take the chance.

Transmission is easy if you are mechanically inclined. My 2021 doesn't have a wire to jump, so the jumper doesn't do anything, but I basically did the same shifter trick (link below) to get my car to show the transmission reached temp to drain. I don't really remember, but you can probably ask your local Toyota Parts department to print the instructions.

https://www.youtube.com/watch?v=eRxSu4-4ojo

SAE 75W is just a monograde viscosity rating and in this case it is specific to ensuring the right viscosity in cold conditions (W = winter rating, is actually a different standardized test from the normal rating).

Multi-grade oils have specific additives that help maintain a “relatively” consistent viscosity across temperature range.

Toyota doesn’t spec multi grade viscosity because it is isn’t critical. Adequate flow is at cold temp is ensured by the 75W rating and the use case allows for the oil to thin more than a multi- grade oil would at operating temps.

If you are in a very warm climate and/or are loading the vehicle heavily you are better with a “thicker” grade (it’s still thinner than when cold… again different tests for W rating and normal).

75W-90 is perfect for both diffs and 99% of real world use cases. You could run 75W-140 if you wanted to and it would not cause any issues. It would provide better protection under extreme heat and stress, at the cost of extra fluid drag/fuel economy hit.

For both Diffs: GL-5

Just a moment...

Note the 40*C and 100*C viscosities of 100 cSt and 16.5 cSt for 75W-90.

Transfer Case: GL-4 (guessing)

Just a moment...

40*C and 100*C viscosities of 39 and 7.5 centistokes - much thinner than the diff gear oil.