Question, Ford for years spec'd 75w-140 for their diffs. Even going so far as to back spec the rears that came with 80w-90 to 75w-140. Well in 2015, they switched to 75w-85. Is this purely for fuel economy reasons ? I bought AmsOil 75w-110 to put in my rear thinking it was the same 75w-140 because I dont tow heavy at all when I do. So why the extreme switch to the thinner lube ?
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