Synthetic vs Dino in diffs: myth or not

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In my Liberty, I've always ran Dino in the diffs. Was told on the Jeep forums (and read it on a few of the high end axle builder's sites) that Dino sticks to the gears better and therefore dissipates heat better than synthetic. The liberty has 222k miles on it on the factory axles running 85w140 in every condition, so I guess it worked! I'm looking to change diff fluids on my JL Wrangler soon and am wondering about that debate again. Is that just a myth or outdated thinking?
 
Myth and outdated thinking, but typical from gurus at various websites with cult like 'followers' pushing ideas or products. It it climbs/sticks too much, it'll starve other areas.

I'd dump that 85w140 for a 75w140. The grades will have different viscosity curves... visc at any given temp. Some gearboxes just last longer when cooler, thicker, or both.

The power to make any ATF, gear oil, PSF, or motor oil climb to Everest's peak!

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In my Liberty, I've always ran Dino in the diffs. Was told on the Jeep forums (and read it on a few of the high end axle builder's sites) that Dino sticks to the gears better and therefore dissipates heat better than synthetic. The liberty has 222k miles on it on the factory axles running 85w140 in every condition, so I guess it worked! I'm looking to change diff fluids on my JL Wrangler soon and am wondering about that debate again. Is that just a myth or outdated thinking?

I think it’s old school out of date thinking IMO. My 3/4 ton Cummins Ram states synthetic gear oil. I’ve used Mobil 1 75w90 and Mystik 75w90. I pull an 11k TT with it and it seems to be ok. I’m guessing more abuse than your Jeep sees 🤷‍♂️

Just my $0.02
 
The last Eaton limited slip differential carrier assembly that I installed came with instructions to use Dino only instead of synthetics. That wasn’t a myth.
 
Could care less what eaton, or certain diff manufacturers recommended. To force something, one should be able to provide proof. Most were simply talking out their farter. Some ol' timers didn't want to flow with the 'synthetic movement'.
 
My mustang came from the factory with synthetic rear axle juice , even had a sticker on the pumpkin stating so !
so thats what i replaced it with....
 
Could care less what eaton, or certain diff manufacturers recommended. To force something, one should be able to provide proof. Most were simply talking out their farter. Some ol' timers didn't want to flow with the 'synthetic movement'.
If your positioned in life that money means nothing then sure ignore what manufacturers recommend and if their is a failure then who cares, correct? My investment and labor meant something to me totally restoring my Chevelle. I’m not positioned and/or willing to operate otherwise.
 
Myth likely conjured up out of misguided thinking by backyard shadetree tribologists. Fact is that conventional is less shear stable, less thermally stable, and has a lower pressure-viscosity coefficient everywhere above ~140°F, all parameters that are critical to a good gear oil. There is zero advantage to using conventional over synthetic.
 
Myth likely conjured up out of misguided thinking by backyard shadetree tribologists. Fact is that conventional is less shear stable, less thermally stable, and has a lower pressure-viscosity coefficient everywhere above ~140°F, all parameters that are critical to a good gear oil. There is zero advantage to using conventional over synthetic.
I wouldn’t categorize the Eaton Corporation as “shadetree tribologists”.
Copied from the Eaton Corporation website:

What kind of oil should I use in my Posi? Can I use synthetic oil? Do I need friction additive/modifier?​

  • A quality, petroleum-mineral based, GL5 rated 80w-90 gear oil should be used.
  • It is necessary to add a four-ounce bottle of friction modifier for optimum performance (if friction modifier has not already been added to the petroleum-mineral based gear oil that the customer selects).
  • While some customers have found that synthetic oil works well in this application, Eaton has not confirmed under test conditions that all synthetic oils (with added friction modifier) are compatible with Eaton Posi applications.
 
I wouldn’t categorize the Eaton Corporation as “shadetree tribologists”.
Copied from the Eaton Corporation website:

What kind of oil should I use in my Posi? Can I use synthetic oil? Do I need friction additive/modifier?​

  • A quality, petroleum-mineral based, GL5 rated 80w-90 gear oil should be used.
  • It is necessary to add a four-ounce bottle of friction modifier for optimum performance (if friction modifier has not already been added to the petroleum-mineral based gear oil that the customer selects).
  • While some customers have found that synthetic oil works well in this application, Eaton has not confirmed under test conditions that all synthetic oils (with added friction modifier) are compatible with Eaton Posi applications.

Dynatrac has the same recommendation.

 
I wouldn’t categorize the Eaton Corporation as “shadetree tribologists”.
Copied from the Eaton Corporation website:

What kind of oil should I use in my Posi? Can I use synthetic oil? Do I need friction additive/modifier?​

  • A quality, petroleum-mineral based, GL5 rated 80w-90 gear oil should be used.
  • It is necessary to add a four-ounce bottle of friction modifier for optimum performance (if friction modifier has not already been added to the petroleum-mineral based gear oil that the customer selects).
  • While some customers have found that synthetic oil works well in this application, Eaton has not confirmed under test conditions that all synthetic oils (with added friction modifier) are compatible with Eaton Posi applications.

Considering when I spoke with one of their engineers, who insisted "synthetic is too thin for gear oil", I'll stick with my comment of shadetree tribologist. Just because you're an engineer doesn't make you a tribologist. They're likely basing that recommendation on the same myths that get spewed around here from time to time.

I'm basing what I stated off conversations with actual tribologists. Three different sources, all with 20+ years in the lubricant industry, and all said the same thing. "Eaton is full of s...."
 
If someone has an gear oil related failure with an Eaton diff, they can quote you (name?) and that will be credible information for the Eaton Corporation to issue a warranty repair/credit?
Eaton has produced automotive differentials for the automotive world at least from the early sixties.
But….I’ve learned today that they are full of….what?
 
If someone has an gear oil related failure with an Eaton diff, they can quote you (name?) and that will be credible information for the Eaton Corporation to issue a warranty repair/credit?
Eaton has produced automotive differentials for the automotive world at least from the early sixties.
But….I’ve learned today that they are full of….what?
On the other hand as long as the grade and specification is what’s recommended then there won’t be a lubricant related failure due to the base stock. It’s simply not going to happen.
 
The guy that rebuilt my jeeps rear axle and does it for a living also said no synthetic. I always put synthetic in it. Maybe that why it failed early?

I originally told him I was going to put Amsoil in it since I had plenty and he said not to.
 
The guy that rebuilt my jeeps rear axle and does it for a living also said no synthetic. I always put synthetic in it. Maybe that why it failed early?

I originally told him I was going to put Amsoil in it since I had plenty and he said not to.
Another person that just really doesn’t know what they are talking about and on a rather fundamental level.
 
After decades in the Fleet industry dealing with factory reps over premature failures, recalls, and just sorry vehicles is what has forged my opinions. In my experience it’s always good insurance to use lubes the manufacturer recommended. There’s going to be questions regarding that practice when settling warranty claims but proof was in our ledger for contract purchases supporting the actual purchase of recommended lubes.
 
You warranty guys amuse me. If your whole moto is stick to the manual and fear the warranty, then why are you on this board?

Aside from the fact that you won't have an oil related failure, I would love to see them find a way to determine it's a synthetic base oil. Most of the 75W-90 gear oils are group III (mineral) based anyway. They'll find a reason to deny your warranty long before the oil comes into the conversation.
 
You warranty guys amuse me. If your whole moto is stick to the manual and fear the warranty, then why are you on this board?

Aside from the fact that you won't have an oil related failure, I would love to see them find a way to determine it's a synthetic base oil. Most of the 75W-90 gear oils are group III (mineral) based anyway. They'll find a reason to deny your warranty long before the oil comes into the conversation.
Shouldn’t you then exercise your authority and ban me?
You must be the BITOG SECURITY POLICE!
…typed with fearful trembling hands….

When 250+ vehicles are purchased annually from a manufacturer that met bid specifications, one should adhere to specific service intervals and recommendations by that manufacturer.
That’s called developing a partnership for generous considerations related to warranty and non-warranty repairs to save taxpayers’ dollars and reduce downtime for a law enforcement-public service fleet.
I really would have been fired if that partnership would have been severed.

Don’t think it matters what a self proclaimed keyboard security policeman on BITOG thinks…

Just folks talking about their automotive stuff is all this is…

Get in touch with reality please.
 
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