I'm getting ready to change gear oil, tranny fluid and transfer case fluids on my 03 6.0 litre. Does anyone know if Ford uses synthetics from the start. And what weight oils are best?

 

Gear oil is syn, I imagine the ATF in the trans and xcase are a syn too. In any case, I used RP in mine. The front axle takes a lighter fluid than the rear, I think it was 75w140 rear and 75w110 on the front. Royal Purple didn't have the exact fluids, but the 75w140 and the next lightest have been running fine in mine.

 

Front D60 takes 75W90 Rear 10.5 takes 75W140 and the Transfer case take ATF. I used Amsoil ATF for my T case. I also used Amsoil severe gear for the front and rear diffs. Ford specs on synthetic lube in the diffs.

 

Anything in particular for use in a man tranny?

 

They used Mercon in '03 but now you need MerconV in the tranny. Some people use syn.