Drivetrain & coolant fluid replacement
 

2008 screw 5.4, 4x4

The differentials say to use 75-90...I am thinking about using valvoline synthetic 75-140.

Transfer case says use motorcraft transfer case fluid but I've read use royal purple, mercon v, etc...what do y'all think because the forms are contradicting.

coolant says motorcraft gold...I just want to use the best possible, like a 100k coolant, suggestions?

Be careful on the transfercase fluid. I've read it is a sure fire way to need a new one, using the wrong (Anything but Ford Transfercase fluid) Fluid.

I'm 2wd and my 3.73/9.75 " diff called for 75w140. I used Lucas with 4oz of the Motorcraft limited slip additive.
Coolant can be MC Gold or Zerex g-05. I used the G-05.

You can use 75w-140 full synthetic in the rear, as that's what Ford changed the spec to in the mid-late noughts (from 80w-90), I think in part because they had a rash of soft axles in the Panther cars. I used RP with LS additive (not that I have much left in the LS at 154k anyway) in the rear because Autozone had a sale, if not I would have used Mobil 1 full synthetic. Personally, I prefer Redline fluids the best out of all of them (that's what I run in my Olds, GMC and BMW). I forget what's in the front, 75w-90 I think? I used Mobil 1 for that. The autoparts stores don't list gaskets for the front diff (because there isn't one) but you can use the gasket for a Ford 8.8 up there.

The Zerex in the cooling system is fine, meets the Ford spec.

Use ONLY Mercon (NOT Mercon V, LV, ULV, or SP) fluid, which you can get at Advance. Or, according to the Motorcraft website, you can use Motorcraft Transfer Case Fluid (XL12). Use of Mercon V in these transfer cases has been known to grenade them.

https://www.fcsdchemicalsandlubrican...ission%20Fluid

Why don't you just do what the Ford factory recommends? There's no magic out there. The "forums" are just a bunch of people who might or might not know what they're talking about. Like me.

As far as the fluids go. I use Motorcraft for the coolant, power steering, trans, and engine. Mobil 1 is also an excellent choice for the engine. I did use Royal Purple for the diff, because it's a good alternative, has the friction modifier in it, and I couldn't get by the dealer.