Dino or Synthetic in Differentials

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Diffs don't run that hot to begin with.
There are some that have had issues and they call for syn oil. Nissan tried to use regular oil in their titans but had problem so they switched to a 75w140 syn.
 
Originally Posted By: Miller88
Some people think the synthetic "washes" off the gears and is worse if you are towing.


Only on the "spin cycle". If you have the newer front loader style differential you'll be okay as long as you only use "HE" grade lubricants. Remember, only you can prevent ring-around-the-gear in your differential.
 
Great info, MolaKule.

Is it just me, or do all of you also think that you want MolaKule to be your Internet bestie?
 
I was surprised how hot the vettes diff ran. After on the highway for a couple of hours my ir gun showed 210. Its got a 4.56 gear though. I think I'd be interesting if we could get a thread going on diff temps.
 
Originally Posted By: turtlevette
I was surprised how hot the vettes diff ran. After on the highway for a couple of hours my ir gun showed 210. Its got a 4.56 gear though. I think I'd be interesting if we could get a thread going on diff temps.



And the problem is.....?
 
I was told some custom axle manufacturers like Currie and Dynatrac require conventional gear lubes, believing dino oil helps sink the heat away more effectively so the gears run cooler.

Thanks for the helpful info.
 
I frequent some Jeep forums so hopefully we can shed some more light on this.

An individual user who is deeply respected in the Jeep community began posting on multiple forums the results of some field trial work from Currie Enterprises regarding their rear ends. Allow me to paraphrase: According to Currie, they were having a higher than normal ammount of failures in their rear diffs and built a rear-end dyno to see what was happening. The stated common thread in all of the failures was the use of "synthetic" gear oil. They claimed to have measured sump temps along with ring/pinion temps and observed that while the synthetic gear lube ran substantially cooler in the sump, the acutal ring/pinion were running hotter. They therorized the synthetic was blanketing the pinion and not extracting heat and dispersing it throughout the pumpkin. Hence they concluded the conventional gear oil allowed the ring & pinion to run "cooler" and attached this stipulation to thier warranties hence forth.

Like everything else on the internet, this exploded into an urban legend and got recycled and repeated over and over and over. It's now engrained in every Jeep web forum known to man.


The problem is that NOBODY can/has posted or has access to Currie's data or knows for certain what was and wasn't tested. There is so much foke lore with no substantiaton surrounding this phenomenon and it keeps getting repeated without question. This is further complicated by most of the general public's lack of lubrication understanding. It seems to apply mostly to the Ford 9 inch rears high pinion setups with steep aftermarket gears (4.56+).

Jim Allen and MolaKule here on BITOG has posted some outstanding responses to these obesrvations. Most diff builders appear to not have much scientific basis but more of a cause/effect position in regards to lube recommendations.

I've searched high and low for a conclusive answer to this theory and have yet to come across anything conclusive.
 
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Originally Posted By: turtlevette
I was surprised how hot the vettes diff ran. After on the highway for a couple of hours my ir gun showed 210. Its got a 4.56 gear though. I think I'd be interesting if we could get a thread going on diff temps.



Was this on a C5/6/7 torque tube/transaxle set up, or an earlier, 'standard' front mounted gearbox/driveshaft/rear pumpkin C1/2/3/4??
 
I think synthetic vs. conventional means next to nothing in most differentials. Fluid level, lack of contamination, presence of proper additives for LS/lockers, and being the correct weight for the application/use probably matters a whole lot more.

One of my trucks has synthetic in it, one conventional. I use whatever is convenient and makes the most sense to me at the time.
 
Originally Posted By: dailydriver
Originally Posted By: turtlevette
I was surprised how hot the vettes diff ran. After on the highway for a couple of hours my ir gun showed 210. Its got a 4.56 gear though. I think I'd be interesting if we could get a thread going on diff temps.



Was this on a C5/6/7 torque tube/transaxle set up, or an earlier, 'standard' front mounted gearbox/driveshaft/rear pumpkin C1/2/3/4??


C3. And they also have a huge problem with side yoke wear. The tire puts pressure on the yoke against the center pin and wears the yoke to the snap ring.

Vett people say there is no oil that will prevent it but I don't believe that.
 
Originally Posted By: MolaKule
Originally Posted By: Miller88
Some people think the synthetic "washes" off the gears and is worse if you are towing.


Some people have no idea how gear lubes actually work.

http://www.bobistheoilguy.com/forums/ubb...tion#Post729255



Gear lubes don't wash off of anything because of their tacky components.

Synthetic lubricants have a slightly higher thermal conductivity than do their mineral oil counterparts.

The calculations below were done for a majority PAO lubricant verses a mineral oil:

Originally Posted By: From Mola's 7/02 thread


Using the Heat Conduction formula:

H = kA(To-Ti/L),

where H is heat Power in W.m, k is heat conduction coefficient in W/meter-squared/C, and temps in C. The k for synthetic oil is 0.16 and k for dino is 0.128, To is temp out of a journal bearing = 100 C, and Ti was oil temp into bearing = 80C, representing a temp rise of 20C, which is a rule of thumb. L is the thickness of the oil film which is on the order of 1um at high loads. A is area of film assumed to be a patch of area of 1 mm squared.

Hs = conductive heat transfer of synthetic oil in W = 3200 W,
Hd = conductive heat transfer of dino (mineral oil) in W = 2560 W.

Therefore, synthetic oil is 20% more efficient at conductive heat transfer than mineral oil.


The same film thickness for both dino's and synth's was used for the calculations.



Also see:

Gear Tribology and Lubrication II
 
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