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Old 07-10-2020, 09:54 AM   #2
MikeN
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Join Date: Oct 2007
Location: Marietta, GA
Posts: 781
Re: Synthetic gear oil in old crusty rear end.

Differentials in old cars and trucks will last for decades, and hundreds of thousands of miles, with the original 80w-90 conventional gear oil. Most old cars and trucks never even had the gear oil changed, and still they lasted forever. I don't see any benefit to spending the extra money for synthetic. I run 80w-90 conventional in all my old vehicles.
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