which oils to use?

I dont seem to be finding what i want with a forum search so i figured id ask it outright in a new post.

I have a bone stock 59 cj5 with fhead engine, t90a 3 speed trans, dana 18 transfercase, dana 25 front axle and dana 44 rear axle.

Which fluids should i be using in each of these parts on my jeep. since sae 30 motor oil is hard to find ive been using 5w/30 for the engine, my owners manual says i should use sae 90 GL4 in the transmission transfercase and both axles but i cant find anything but sae 90 GL1 at anyplaces that ive checked. what are you guys running in your stock jeep? or does anyone know where i can find the correct stuff my book calls for and maybe a part number?

 

I recall 85-90 throughout being the recommended oil for trans, t case, axles. Can't comment on engine, but I'm running 10w40 in my 225.

 

I have 69 fhead I found straight 30w and ran it all summer but am going to 10-30w for winter haven't found any thing that says I shouldn't

 

I run 20w50 in my engine. But then I run in a really hot part of the country with mine.
My book (Chiltons JEEP CJ 1953-79) says use 80w-90 gear lubricant (API GL-4) in the Tranny/TC. Doesn't say for the differentials.
My other book (Haynes JEEP CJ 1949 thru 1986) says the same weight - 80w-90 but in API GL-5 for Tranny/TC.
For the Differentials it says 80w-90 API GL-5 for conventional diffs and API GL-5 Limited-slip for Trac-Loc diffs.
You might consider sending an email to Herm about it, seeing as how he works with gears and all.

 

I run 10w40 in my engine and it's a simple trans and rearends any 80-90 or 85-120 wt gear oil will work, there made much better than when your jeep was made

 

Would it be beneficial to run synthetic in these old engines?

 

I would not try it, you may find leaks in places you never had a leak before.

 

^lol! Good thinking.

 

If GL-1 is all you can find, then by all means run it! Seems that the higher the GL number then the higher the content of EP modifiers. That is Extreme Pressure. There really aren't extreme pressures in an old JEEP. So you really don't need the higher GL numbered stuff.