Gear Lube confusion

[wpurple]

I just changed the axles on my Exploder from 3.27 to 3.73(non-locking)
According to the manual footnote 3
"Vehicles equipped with 4.0L SOHC or 4.0L EFI engines and 3.73 or 4.10 rear axle ratios or 5.0L engines require synthetic rear axle lubricant....."
The recommended synthetic lub is Motocraft 75W140

...I just filled it with 80W90 Mobil 1 as I have in the past with the 3.27

Why such a heavy oil for 3.73? Does it really matter since it's not a LS?

HELP

Kurt

 

[aldive]

I use the same Mobil 1 as you added to yours in my 3.73 LS rear.

Works great.