Why 75w-140 in my Diff??
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Senior User
Joined: Nov 2003
Posts: 165
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From: Illinois
Why 75w-140 in my Diff??
I have a 99 F-350 DRW, and according to my manual, requires 75w-140 gear oil. Ford dealer told me it never needs to be changed unless it was submerged in water, but I want to do it anyway, if for no other reason that to feel better about it and also get rid of any wear material. I just want to know why they want this weight of oil in it instead of the typical 80-90 like my front end uses? It seems like one could get substantially better mileage out of the lighter weight oil. Apparently it just doesn't protect like the heavier stuff does? Even semis use 80-90 generally..! If someone could shed some light on this, I would greatly appreciate...
Thanks,
Matt
Thanks,
Matt
Posting Guru
Joined: Nov 2002
Posts: 2,440
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From: Ventura County, CA
I narrrowed it down to Amsoil or Royal Purple. Neither one requires the friction additive, as they already have it in them. I priced both. Jeg's (free shipping) had the best price: $8/qt. for RP and $12/qt. for Amsoil. I bought 4qts. of RP from Jeg's; cost me $40.35.
BTW, it's going in today along with the Diablo shifter valve...
BTW, it's going in today along with the Diablo shifter valve...
Senior User
Joined: Jan 2004
Posts: 225
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From: Middle Geogia
you should have had the amsoil guy sign you up as a preferred customer. Most of us will do this at our expense. Then the oil would have cost you less. Also, Amsoil provides a warranty, not to just replace your oil like Mobil 1, but that it will pay for parts and labor if their is excessive wear due to using its product. This warranty applies to Amsoils extended drain interval. The other companies tell you to replace the oil according to manufacturers guidelines.
Postmaster
Joined: Nov 2001
Posts: 4,742
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From: OK
The specs quoted are required for the SRW Sterling axle for sure, but I didn't think the Dana rear of a dually required synthetic. Obviously, I could be wrong. But you should check again to make sure you are reading the info for the correct axle. No need in spending mega-$$$ unless you have to.
