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Old 08-26-2018, 10:26 AM
hat_man hat_man is offline
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Posts: 153
Default Rear gear oil change

Not trying to start a big debate on the difference between synthetic and conventional products, there's enough of those out there already. It's hard wading through all the internet junk and opinions when most of what I can find is so outdated.

My truck has the 3.73 rear (I was thinking of a re-gear but it won't be anytime soon now) and typically does 600 miles a week on the highway. I don't tow anything and every once in a while haul things, but usually only a couple hundred pounds.

I'm switching over to synthetic fluids and was finding only anecdotal evidence for leaving the rear gear fluid conventional. I'm only asking for your experiences with the two. Or links to something verifiable that I can read to help me make a final decision.

The other question is, beings my used truck didn't come with an owner's manual, what weight? I think it's (75 or 80)w/90 but what is the 75w/140 I'm seeing? Is that for just towing or off-road when the gears get really hot? Or for limited slip or posi-trac or locker? I don't have any of these. Just a plain old 3.73.

Thanks.
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Old 08-26-2018, 12:23 PM
Logan03CO Logan03CO is offline
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Default Re: Rear gear oil change

beings my used truck didn't come with an owner's manual, what weight? I think it's (75 or 80)w/90 but what is the 75w/140 I'm seeing? Is that for just towing or off-road when the gears get really hot? Or for limited slip or posi-trac or locker? I don't have any of these. Just a plain old 3.73.

Thanks.[/QUOTE]

Fyi
the Link to owner manuals are located as a sticky in the general ford ranger discussion section of the site.
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Last edited by Logan03CO; 08-26-2018 at 12:27 PM.
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Old 08-26-2018, 03:26 PM
hat_man hat_man is offline
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Default Re: Rear gear oil change

I didn't even think of that. SMH

Thanks Logan.


Looks like it says approx 3 quarts (5.0-5.3 pints) of 80w-90. Any problems with using 75w90 synthetic?
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Little Black Ranger: R.I.P Born-1997 Died-2018. 297k miles of good times. You will be missed.

Oh Deer: 2003 XL 2.3l Duratech, 5-speed stick w/OD. Current mods: Body work after hitting a deer 12 hours after I bought it.
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Old 08-26-2018, 03:33 PM
Dirtman Dirtman is offline
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Default Re: Rear gear oil change

No issue using 75w90, it's simply the synthetic equivalent of 80w90. I recommend mobil one or amsoil 75w90 for almost any diff. No additives needed for limited slip rears.

Ford "changed their mind" on recommended gear oil recently and suggests 75w140 now for almost everything, even older diffs that were using regular 80w90. I have no idea why since 80w90 has been proven reliable for over a century. Makes no sense to me to switch to a heavier weight oil so I stick with 75w90 synthetic.

Im no oil expert but an 80w90/75w90 will operate the same as a 75w140 cold but be thicker at 100*c so perhaps it might be useful in extreme climates or towing conditions but again... 80w90 has worked fine so....

Last edited by Dirtman; 08-26-2018 at 03:39 PM.
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