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New owner of a wildcat 4, as posted in another topic. I am getting ready to do fluid service before I begin using it. What diff fluids are yall running? It says Hypoid 8090 in the manual, but as we all know there are a LOT of those!
 

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Everyone has a favorite brand of oil, so I suspect you'll get a number of recommendations.

Redline products are widely used in my former hobby, sports car road racing. Drawing from that background, I use their stuff for equipment that sees a lot of stress, like the 1000 or X diff. Their Heavy Shockproof is tough enough to be used in top fuel and funny cars, yet flows like 75w. It is so slippery that it is not recommended in gearboxes with synchros, but that's not an issue here.

So my personal preference aside, buy a full synthetic with a minimum spec of 75w140 GL5 in your favorite brand. That little Tonka-toy diff works hard, and has about two shot-glasses of oil in it.
 

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Everyone has a favorite brand of oil, so I suspect you'll get a number of recommendations.

Redline products are widely used in my former hobby, sports car road racing. Drawing from that background, I use their stuff for equipment that sees a lot of stress, like the 1000 or X diff. Their Heavy Shockproof is tough enough to be used in top fuel and funny cars, yet flows like 75w. It is so slippery that it is not recommended in gearboxes with synchros, but that's not an issue here.

So my personal preference aside, buy a full synthetic with a minimum spec of 75w140 GL5 in your favorite brand. That little Tonka-toy diff works hard, and has about two shot-glasses of oil in it.
In most of my previous vehicles I ran Lucas 85w-140 non synthetic due to its ability to handle heat better than a synthetic. I am no engineer but I look at these small differential and what they do, holding only 6oz of fluid, I can’t imagine how quickly that fluid breaks down! I haven’t run it to get differential temps but 6oz of fluid wouldn’t seem to cool very well. I hav errand in some articles that if differentials are going to be subjected to a lot of heat, not to run synthetic. Synthetic only has the ability to be subjected to thermal breakdowns one time and it’s done. Non synthetic can actually recover from thermal breakdown after cooling and continue being used. Does anyone have opinions on this? High performance and very small amount of fluid, I only want to do what’s best for longevity.
 

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In most of my previous vehicles I ran Lucas 85w-140 non synthetic due to its ability to handle heat better than a synthetic. I am no engineer but I look at these small differential and what they do, holding only 6oz of fluid, I can’t imagine how quickly that fluid breaks down! I haven’t run it to get differential temps but 6oz of fluid wouldn’t seem to cool very well. I hav errand in some articles that if differentials are going to be subjected to a lot of heat, not to run synthetic. Synthetic only has the ability to be subjected to thermal breakdowns one time and it’s done. Non synthetic can actually recover from thermal breakdown after cooling and continue being used. Does anyone have opinions on this? High performance and very small amount of fluid, I only want to do what’s best for longevity.
Let me just say this for the newer members. The Wildcat diffs are prone to failure due to AC using quad parts. We all know this, and a lot of us have gone through diff failures (me included). The very best thing you can do is change diff fluid often, minimum once a season, but definitely more if you're hard on your equipment.

The site's Subject Matter Expert - SandandSea (Robert) has more experience with these diffs than everybody put together! He is always willing to help out. He has some write ups that I made stickies so they are easy to find. If you get stuck, or need help, PM Robert.

Diff fluid is just like oil discussions, everybody has a favorite, so use what you like. My only advice is change it often.
 

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FlyingFlea, that is the first time I've read that non-syn handles heat better than synthetic. The most severe real-world test for an oil is, IMHO, a powerful turbocharged car. A car will go through hundreds of heat cycles between oil changes, and heat in the turbo center section is extreme.

I haven't researched this extensively, but all that I am aware of specify synthetic. Many warn to only use synthetic oil.

Lucas Oil's own product info does not mention high temp capability on their non-syn gear oil, but makes exactly that point on their full syn gear oil.
 

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FlyingFlea, that is the first time I've read that non-syn handles heat better than synthetic. The most severe real-world test for an oil is, IMHO, a powerful turbocharged car. A car will go through hundreds of heat cycles between oil changes, and heat in the turbo center section is extreme.

I haven't researched this extensively, but all that I am aware of specify synthetic. Many warn to only use synthetic oil.

Lucas Oil's own product info does not mention high temp capability on their non-syn gear oil, but makes exactly that point on their full syn gear oil.
Unfortunately I have nothing scientific on this. I have been told it many time by competition diff builders over the years. They have stated that as a synthetic can keep gears cooler. However, should a diff get hot the regular oil still clings to the gears providing better lubrication and heat dissipation where as synthetic can no longer cling. Also, they have stated that if moisture was introduced to the system the standard oil does a much better job of staying Separated from the water and protecting where the synthetic will blend with the water and greatly reduces protection. There are axle manufacturers that actually void warranty if a synthetic oil is used in high performance applications. I understand ALL this is contrary to what marketing claims, but I feel like those who analyze failures and build high performance diffs to last May know better, the real world effects. The first company to tell me this was Fearless gear in ca, near where I live. There statement is mildly supported by this article.
 

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I think the "gold" in that article is at the end, and it directly applies to the 1000 / X diff:

"The only synthetic's I would consider are Amsoil, and redline, along with some industrial synthetic's that aren't really marketed to your everyday user. But would only consider if I was trying to control a heat problem, or shock load issue generally related to doing something the differential was never designed to do in the first place."

The diff in a 1000 / X was not designed to haul around a side-by-side. It was adapted from AC quads.
 
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...interesting discussion on synthetic /non synthetic... since years most brands wanna buy us best full synthetic blabla...
(specially KTM to buy only most expensive motorex fullsyn.)
in november i changed to liquymoly 5-50 motoroil- i was surprised its only half synthetic...
i mailed liquy moly and a tech gave me an interesting answer that this stuff has some better abilitys then the full synthetic !??
i will believe him....
btw- in my us car shop they have some GEAR oils - not spec. saying diff oil- is it the same like differential oil?? 20191103_152444.jpg
 

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How about the rear transaxle? I keep reading AC fluid is the only choice.
Trails/sports have a rear transaxle that gets ac rear transaxle fluid. Front and rear Differentials take a gear oil.
 
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...this good? says limited slip- didnt see when buyin...!? 20200816_160124.jpg
 

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My understanding is that ltd slip oil has friction modifiers that help the clutch-packs found in most ltd slips function. Those additives don't have much (if any) downside, they just aren't needed.
 
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-Those additives don't have much (if any) downside, they just aren't needed.-

..thats what i wanted to hear...thanx ;-)
 
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