I use 75w90 in all 3. Whatever synthetic brand is on sale.
I think the rear in mine is a mix of 75w90/80/140 because I had 3 different types in my garage. Front is Walmart Supertech and transfer case is Mobile 1.
I would just top it off and then do a few drain and fills. Yours an 04 so will need Type-IV fluid or equivalent. I've had success using Amsoil signature series ATF.
What color is your fluid? If its still red and doesn't smell burnt you should be good.
Ive seen a lot of people use Blue Devil (not the pour and go version) with success on these 4.0s. I had a bottle ready to go but ended up just replacing my HGs at around 140k. My head were also warped. Had them resurfaced and so far so good.
Blue Devil Head Gasket Sealer: 1 Year Later - YouTube
Nice. Yeah I believe Addco and SuperPro make thicker rear bars for our 4runners. I have also been looking into a thicker rear bar. Just waiting on a good time to buy one.
I have also slowly been going back to stockish or what I would call OEM+. Sold my front bumper, got smaller tires, removed...
I used to run no sway bars and it was sketchy driving on the backroads or making any sudden maneuvers. Then I installed my PCK and it was way better. Then I put my rear sway bar back on. Then after awhile I put my front back on. I did the whole cycle lol.
I watched this on youtube who did a...
You can buy the Aisin part from rock auto for about $90. Aisin is the OEM manufacture. I replaced mine when I was doing my cooling system overhaul, but there was nothing wrong with it.
The fan clutch usually doesn't go bad that early. Its pretty easy to replace though.
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The dipstick should also say Type-IV on it.
When I did mine I changed it with Amsoil signature series ATF. Its been a few thousand miles already with no issues at all.
Im honestly a fan of the scanguage. I have it set to read my trans temp, coolant temp, voltage, and mpgs. I have it right behind my steering wheel so its always in view. It keeps my phone free so I can keep it away or in my pocket.
It can also read and clear codes if they ever come up.