Which synthetic in the diff?
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Senior User
Joined: Jan 2008
Posts: 499
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From: southeat Ga.
Which synthetic in the diff?
I need to change the fluid in my rear diff but which one? They come from the factory with synthetic right? (03 F250) I don't have limited slip if that matters. I looked at a few different ones today and saw that Royal Purple is over twice the price of Castrol Syntec, is it worth that price? I assume I have the Dana 80? Should I get something especially for high mileage? (236,000) How much do I need anyway? I know to fill until it comes out of the fill hole but will I need 2 quarts? 3? 4? It's a pretty big chunk back there. Thanks for any info.
Senior User
Joined: Sep 2007
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The rear axle calls for 75w-140 full syn. Since you don't have LS the lowest cost quality brand should work. Here is a link to a recent post about servicing the axle, complete with pictures. Might be a good time to upgrade to the Ford aluminum cover. At least you will only have to clean the sealer off of the housing!
https://www.ford-trucks.com/forums/8...with-pics.html
https://www.ford-trucks.com/forums/8...with-pics.html
Elder User
Joined: Jul 2009
Posts: 919
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From: Smiths Grove, KY
The following website provides a good description and pictures for changing the fluid in the Sterling 10.5 differential.
Welcome to guzzle's Rear Differential Maintenance Web Page
Welcome to guzzle's Rear Differential Maintenance Web Page
Lead Driver
Joined: Dec 2006
Posts: 7,092
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From: San Diego, CA
I did the same thing, but it took 4qts to fill 'er up...
Junior User
Joined: Mar 2009
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From: Kona, Hawaii
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Post Fiend
Joined: Mar 2009
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From: Mt. Shasta California
Same thing but check your door sticker and diff tags to see what you have first.......codes are in here.
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Posting Guru
Joined: Oct 2009
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From: Tonoph,AZ
Amsoil
i ordered amsoil severe gear oil 75w140 last nite at www.lubedepot.com. it was $15.15 a quart. the only reason i went with this is because i have seen quite a few of the regular members on this site have it in there gearboxes with great reviews. with a stock diff cover it should take 7 pints or 3.5 quarts. hope this helps...
Postmaster
Joined: Oct 2009
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Yeah, real synthetics are worth it. Real synthetics include: Amsoil, Redline, Mobil1, and Royal Purple. Syntec, and that new penzoil stuff and the cheaper synthetics are not really synthetics, they are highly refined conventional base stocks with add packs to make them behave more like a synthetic, which only works till the add pack breaks down.
I got a consistent 1 mpg better when I changed my rear diff to Mobil1, and that was repeated when my front diff was changed over.
I got a consistent 1 mpg better when I changed my rear diff to Mobil1, and that was repeated when my front diff was changed over.
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