DOC4444,

This has been strongly suggested by a good friend that is quite knowledgeable about lubricants. In fact, he is an Amsoil distributor.

Makes him know almost nothing about oils but trying to line his wallet with your $$$.No locker/LSD company recommends synthetic,heck Detroit only recommends dino.

Actually tjkj2002, my friend is alot more knowledgeable about oils than you give him credit. I've checked with him this evening and he firmly supports his position on synthetics in differentials, regardless of what Auburn says. For Auburns, use non-synthetic, all others, unless stated otherwise, synthetics are okay.

I will be adding the Amsoil Severe Gear 75W-90 to both the front/rear diffs on my KJ. You are welcome to do as you wish with yours. But denegrating my suggestion and my friend's integrity will stop right here.

Hoosier CRD

I'd be very interested if your friend has Data - i.e. something with numbers - measurements???????
not at all interested in Opinions.

although I will give Tj credit - that's the first time I realized Detroit had a preference on Synthetic vs Dino
Corporations have resources to test stuff and have legal warranty repercussions if they're wrong.....

Call Currie and ask what to use in there diffs,then call Hi9 and ask them what gear oil to use in there diffs.Both make diffs that see more extreme conditions then most will ever and yes both only recommend dino 85w-140 or no warranty.For a low pinion axle you may get 100k trouble free miles but if you ran dino you will get 200k-300k trouble free miles.Synthetic is only good in a forced oiled system(like your engine and trans) but a splash oiled system everything that makes syn good makes it very undisireable.

Short answer is "Yes". What data would you like to see, ATXKJ?
Hoosier CRD

Actually that's a good question - because the folks saying Synthetic is not good - generally don't give a reason, I wonder if Eaton would give a reason?

So the quick response would be just lifespan data on differentials Dino vs Synthetic - probably under high stress conditions.

I'm not sure what oil property would distinguish between pressure lubricated vs splash oiled.

Short answer: none.

I'm not sure that's totally true - pressure lubricated normally has a filter, splash lubricated doesn't - so if you have contamination - in a pressure lubricated - the filter cleans it up. in a splash lubricated - it's only cleaned - when you change the oil.

so if someone drives through a mud hole - that contaminates the diff - who's more likely to change the oil?
and who's more likely to rationalize a reason not to change the oil?

the guy who spend $20 on Dino - or the guy who spent $50+ on synthetic?

so a cheaper oil - might make the diff last longer - if the person is more willing to change it......

I agree with that, but contamination is not an "oil" property - intrinsic to the oil. Like viscosity or viscosity index.

the properties that make synthetic great in a forced oil system are major flaws in a splash oiled system.

Name one.


Actually I think the differential folks don't know why - I think the places that are really seeing problems are small shops without the resources or ability to analyze why.

now - for me - I'm not racing - I'm not towing - I'm not even driving very fast and at Jeep's oil change intervals I could use anything on the market and not have problems.
although I still like to know why Currie thinks it's a problem

Not wanting to cause any more problems....but here's my input:
Actually you're BOTH right..... the main reason companies like Currie recommend DINO oil as compared to synthetic is because it typically provides better "cling" properties...meaning that, in a rock crawler for example, at LOW speed operation it keeps a thicker film of oil on the parts which translates to more protection..... HOWEVER...if a constant flow is available,such as highway use or drag racing, the SYNTHETIC will give better performance results through better lubrication AND less drag loss due to a freer flow...
just my 2cents...
Tom