rear diff oil

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Reading 2015_PSDs posts about his mag hytec diff covers and fluid change got me thinking that its time to do it in my Ranger which im almost certain has the factory gear oil. As of this morning when i parked it, it has 138,385 miles, so Im sure that gear oil is pretty nasty. Using the axle code found on my door sticker and a chart I found online, I was able to determine that my truck has a 7.5" open differential and 3.73 gears. According to Amsoil I can use 75W90, 80W90, (which I think is factory recommended) and also 75W110. Being its open, does that mean I dont have to use a limited slip additive or gear oil with additive in it? I have some Amsoil 75W90 that is about 7-8 years old, its in the original cardboard box and the bottles are brand new and sealed but its in a deteriorating barn and gets exposed to moisture, should it be ok to use? Or should i step up to 80W90 or 75W110? Also would it be better to use silicone when I put the cover back on or should I use a gasket?
 
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You could use 7-8 year old unopened bottles that had been buried in the ground. The fact that there is still a box is evidence that the bottles are unaffected.

I would use the 75/90. It is suitable for any and all conditions you will be subjecting it to. Thicker would only be appropriate for use in very high temperatures, under very heavy loads.
 
Originally Posted By: mobilaltima
Reading 2015_PSDs posts about his mag hytec diff covers and fluid change got me thinking that its time to do it in my Ranger which im almost certain has the factory gear oil. As of this morning when i parked it, it has 138,385 miles, so Im sure that gear oil is pretty nasty. Using the axle code found on my door sticker and a chart I found online, I was able to determine that my truck has a 7.5" open differential and 3.73 gears. According to Amsoil I can use 75W90, 80W90, (which I think is factory recommended) and also 75W110. Being its open, does that mean I dont have to use a limited slip additive or gear oil with additive in it? I have some Amsoil 75W90 that is about 7-8 years old, its in the original cardboard box and the bottles are brand new and sealed but its in a deteriorating barn and gets exposed to moisture, should it be ok to use? Or should i step up to 80W90 or 75W110? Also would it be better to use silicone when I put the cover back on or should I use a gasket?
In an open differential, you won't need limited slip additive. While I use syn gear oil in several of my trucks, in an old Ranger that isn't going to haul heavy (assuming because I see the Cummins in your sig), I would just use whatever name brand gear oil in the correct weight that you can get a good deal on (my favorite is AAP 80W90 by the gallon, bought with online discount codes). Also, I've used lots of orange RTV on flat steel diff covers with good results.
 
Originally Posted By: millerbl00
After 138,385 miles, its way too late to do much good.
Not sure about that, at my old job they've gotten 300K out of Rangers in commercial service, if it's never gotten water in the diff & it's not noisy, it's probably still OK. I need to change it on the GMC in my sig, it's at 155K on the original gear oil, but it is still fine.
 
Correct, "open" means no need for limited-slip additives.

Solid-axle rear gearsets are pretty rugged, especially non-limited-slip units. The '73 Plymouth that was my transportation from ~78 to 2005 went over 200k miles on its original gear oil in a Chrysler 8-1/4 open rear. When I gave the car away with over 430,000 miles on it, the rear end was still perfectly quiet and had never been open other than the fill port to change the fluid once or twice.

I think if you go ahead and change it with any quality oil, you'll be fine.
 
If the containers are still sealed and the box is intact the probability is that the oil is fine to use. Do not use a limited slip additive in a differential that doesn't need it. LS additives degrade oxidation and seal performance, in a limited slip differential that is just a price to pay for needing the friction perfomance, but you don't need that.
 
I forget when the J300 rating changed (Pablo can tell you), but 75W-110 is the viscosity that 75W-90 used to be before the change. The oil that you have may be old enough to be the old viscosity and if the containers are in good shape, I would use that. My factory covers had silicone only with no gaskets (made the cleanup very easy), and provided the gasket surface on both are in good shape I would just use silicone on it.

Hope this helps!
 
use the amsoil that you found - its fine. think of it this way: even opened, and in use in a rear end, gear oil is good after 7-8 years. 75-90 is great. 80-90 also. no need for anything heavier. according to some testing done by Amsoil, most wear in a differential occurs when the vehicle is new - so that is the most critical time to change it - to get those particles out. there is negligable wear after break in.
 
Originally Posted By: bullwinkle
...if it's never gotten water in the diff & it's not noisy, it's probably still OK.

Exactly.

I would use the Amsoil gear oil you have on hand. It will be fine.
 
A few months ago I gave away 5 quarts of 20 year old, unopened and sealed Redline GL-4 MTL gear oil. A number of people contacted me to put that into their vehicles. Old doesn't always mean no good.
 
That Ranger diff isn't going to be sweating with the oil you have. Run it.

Not all diffs benefit from thicker oil. A metallurgical failure analyst who engineered for AAM for over a decade told me I would be "wasting my time and money" putting anything thicker than 75/90 in my AAM 11.5" and 9.25".

My Jeep is the opposite end of the spectrum, however. I was told never to run anything less than 75/140 synthetic.
 
Use what you have.....your diff will never know the diff
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Not a picky application at all.

Currently my 7.5 equipped truck has Valvoline synthetic 75W90 in it. My D35/8.8 equipped truck has Napa conventional 80W90 in both diffs. I picked those because they were on the shelf at the store.

Use RTV to seal the cover. Ultra Black and Right Stuff Black are both great for this application. All of the aftermarket gaskets I know of for the 7.5 are cut paper.

Shake up a bottle of the Amsoil and see if it turns an opaque tan or brown color ("milkshake")...if it does it has water contamination. If it's fully transparent, it's probably fine to use, but that's your call to make.

By the way, the interval Ford states in the maintenance booklet is 150K miles on the factory fill, so technically you are ahead of schedule still.
 
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I used a Permatex sealant made specifically for differential covers when I serviced the rear on my 04 F150. Worked just fine, and it looked like the prior time it was changed they used sealant as well.
 
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