I recently bought a 2007 f-150 with 36,000 miles on it. I am thinking of changing the rear diff fluid. I personally like to use Royal Purple and I have used that in other vehicles. I have read that there is something we can only get from the Ford dealer for the rear diff. Is that true or just marketing hype to get us to buy from the dealer?

What do you use?

 

The stuff from Ford is Friction Modifier #C8AZ-19B546-A. I only know this because I just changed the fluid in mine earlier this week.

 

Is this required? Or can I just use the synthetic? Is the friction modifier an additive or the oil itself?

What is the capacity of the diff? How much oil do I need?

 

Not sure if it is required but I would get it. It's about $5 for 4 oz. I have been told that Royal Purple already has friction modifier added but I don't know for sure. The amount of differential fluid needed depends on the size rear in the truck. Mine took between 5.5 - 6.9 pints. Just fill it up to the bottom of the fill hole and you are done. The fluid weight should be on the metal tag on differential. Either SAE 75W-90 GL-5 gear lube or SAE 75W-140 GL-5 Synthetic gear lube. Hope this helps.