Why no syth gear oil in the diff? - JeepForum.com
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post #1 of 197 Old 08-29-2009, 12:21 PM Thread Starter
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Why no syth gear oil in the diff?

This has been covered but my search is not turning up threads that give real answers. I'd be grateful if anyone can paste in a thread link that answers the question. Or otherwise answers the question why I shouldn't put synthetic oil in the rear diff? Saw a comment on this recently on JF, from Jerry maybe, who you don't want to ignore.

Everything else is synth on my Jeep (except in the T-case), and I have some synth 75/90 ready to go, but I want to make sure the gears are protected. '

My diff oil doesn't get changed very often since I seldom dunk them, so I want some longer lasting oil. My Jeep sees sub-freezing temps a lot in the winter, and the usual heat in the summer.

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post #2 of 197 Old 08-29-2009, 12:37 PM
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Proven to run hotter than they already do on dino oil. Currie Enterprises won't even warranty if synthetic is used.
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post #3 of 197 Old 08-29-2009, 12:43 PM
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The Word of Jerry is as follows:


"I'm sorry but #1 it's not just Currie that has discovered the heat extraction issue with synthetics and #2, what else would you expect a manufacturer who only makes synthetic lubes to say on the subject?

And finally, who do you think would be the most likely to be non-biased on the synthetic vs. non-synthetic gear lube subject? An axle manufacturer or a gear lube manufacturer who only makes synthetic gear lubes? Personally, I'll trust the axle manufacturer every time... especially one who was as surprised as the rest of us that synthetic gear lubes were causing the problems they observed that go away when non-synthetics are used. To me, that's a no-brainer unless you can't keep an open mind on the subject.

In closing, I am definitely not anti-synthetic. In fact, in one of my most recent answers to what lubes to use, I recommended synthetic lubes in the transmission and transfer case and I recommend a synthetic in the power steering system too. But I'm not so closed-minded to believe that synthetic has to be the best for all applications either as some appear to be either."
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post #4 of 197 Old 08-29-2009, 12:55 PM
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In regards to this anti-synth. being used in a diff., upon Jerry's well respected advice, I put GM's SynchroMesh into my tranny. I'm wondering what anyone knows how much of a problem would be caused using a SynchroMesh instead of just a regular diff. fluid change? I find SynchroMesh works great in my tranny and would love to have a stronger and longer lasting fluid in there, but if the same heat problems would exist as a straight synthetic, I don't want to risk it.

Anyone?


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Last edited by VanBCguy; 08-31-2009 at 02:13 PM.
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post #5 of 197 Old 08-29-2009, 01:14 PM
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Quote:
Originally Posted by WahooCreek View Post
The Word of Jerry is as follows:


"I'm sorry but #1 it's not just Currie that has discovered the heat extraction issue with synthetics and #2, what else would you expect a manufacturer who only makes synthetic lubes to say on the subject?

And finally, who do you think would be the most likely to be non-biased on the synthetic vs. non-synthetic gear lube subject? An axle manufacturer or a gear lube manufacturer who only makes synthetic gear lubes? Personally, I'll trust the axle manufacturer every time... especially one who was as surprised as the rest of us that synthetic gear lubes were causing the problems they observed that go away when non-synthetics are used. To me, that's a no-brainer unless you can't keep an open mind on the subject.

In closing, I am definitely not anti-synthetic. In fact, in one of my most recent answers to what lubes to use, I recommended synthetic lubes in the transmission and transfer case and I recommend a synthetic in the power steering system too. But I'm not so closed-minded to believe that synthetic has to be the best for all applications either as some appear to be either."
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post #6 of 197 Old 08-29-2009, 02:02 PM
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Try this: https://www.jeepforum.com/forum/searc...archid=5806665

I did a search as follows:

Do an Advanced Search
Select TJ Technical Forum
Select User: Jerry Bansford
Search Term: differential synthetic

You will get several threads that have the discussion back and forth.

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post #7 of 197 Old 08-29-2009, 02:21 PM
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i wouldn't take anything that Currie Enterprise says as fact. they are just covering there ***** because people don't break in there gear set properly.

several years ago I had currie build me a ford 8" rearend for my 89 wrangler. I have a 8" 3rd member already build with a detroit locker and 4.10 gears sitting in my shelf. the assembly had been in my 73 torino with a hung out 351 cleavlend in it, till it dropped a valve. anyways, I tired to have currie build me a 8" housing with torino big bearing end on it. he said himself that it could not be done since ford did not make 8" housing with the big bearing ends. never mind that I had one sitting in my yard, in my torino. the car originally had a 302 in it. I probably should have sent him my housiing so it could be shortend for my jeep, but at that point I was done dealing with that know it all. As we would call a "fountain of miss-information".

If you do a proper break in process, you can run synthetic in you differental. when I had purchaced my 08 JK 4 door in september of last year, I had broke the engine in from the drive from el paso TX to Silver City NM, which is about 150 miles. the first oil change was done at 2000 miles and the diff oil was changed to synthetic oil also. I'll change the front diff when I hit 30000 miles as it almost never see's any action in it.

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post #8 of 197 Old 08-29-2009, 02:42 PM
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Quote:
Originally Posted by JohnRodriguez View Post
i wouldn't take anything that Currie Enterprise says as fact. they are just covering there ***** because people don't break in there gear set properly.
That says only one thing... that Currie feels they are better protected against improper break-in with a mineral-based gear lube. More importantly, it's not just Currie that has started requiring dino gear lubes be used to maintain the warranty, Currie was just the first axle builder to go to the trouble to finally figure out WHY a mineral-based gear lube protected the ring & pinion gears more effectively.

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post #9 of 197 Old 08-29-2009, 10:05 PM
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Quote:
Originally Posted by GOLENJEEPTJ View Post
Proven to run hotter than they already do on dino oil. Currie Enterprises won't even warranty if synthetic is used.
I find this statement to be false. Well atleast in my trials. I ran my old d35 on dino oil for 20 miles took a temp reading then ran same route with synthetic and did a temp reading found on synthetic it was 20 degrees cooler.

if they run hotter on synthetic why do the OEM's put syntheic in some of ther axles. Even semis now are using synthetic in there diffs

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post #10 of 197 Old 08-30-2009, 05:11 AM
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Well,

not to stir up the pot, Ive been on the fence as well, because I'd like to run a longer lasting lube.

It has been mentioned before, that the Diff housings actually run cooler with synthetic than with dino, but the gears themselves run hotter. which makes sense, the heat has to go somehwhere, either into the oil or into something metal!

The one thing that I've thought about, is that Currie as well as several others usually manufacture high pinion axles. I would beleive that synthetic doesnt travel as well being drawn upwards into a gear as conventional oil. This doesnt matter in an engine or Tcase/trans, because the fluid is pumped. Stock Jeep differentials arent high pinion, so most of us wont see the difference. However, if the gear oil works better in the high pinion diffs, it will work better in ours as well, but the difference might be less noticeable. Just my take on it.

Also, the OEMs, usually call for 80w90 or 75/140 for towing. 75/140 used to be strictly synthetic, and todays CAFE specs are the hot topic, so its not hard to see why their specing synthetic. as for Transports and the long haul guys, MPG and cost are a big factor for them, and the cost of changing gear oil every few months would add up quickly. but again, it bring back the point that synthetics in some diff applications might not cause the damage that currie claims, seeing how the big rig guys arent experiencing a record number of failures from it.
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post #11 of 197 Old 08-30-2009, 05:43 AM
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Can oil go bad? Cuase I bought like 8 5 gallon buckets of dino gear oil cause everyone was changing over to synthetic, and I bought all of it for 10 bucks.......more like I paid a guy 10 bucks to load it in my truck.
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post #12 of 197 Old 08-30-2009, 05:50 AM
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If you live in an area that gets below zero degrees F in the winter then you had better be running synthetic oil in everything including diffs. Damn what currie says....
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post #13 of 197 Old 08-30-2009, 07:39 AM
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I've been running Royal Purple synthetic in my diffs since 2006 when I lifted my Heep and I have driven many road miles and used my Heep on the farm, pulling my ATV trailer, boats, Hunting and fishing, pulling other stuck vehicles out and offroading in the mud here in Florida all the way to mountains in North Carolina. I have yet to have any problems. Synthetic oil is suppose to have a higher boiling point than regular Dino oil, so why would it overheat faster?
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post #14 of 197 Old 08-30-2009, 07:49 AM
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I have been running synthetic in all of my vehicles for 15 years with no problems at all. I have a '93 Suburban I use to tow my jeeps to the trail head and it has 248000 miles on it and still going strong. My '76 Cherokee is up on 35's and locked front and rear. I have used synthetic in it since I regeard to 4.56 with no problems. I have used synthetic in my 2006 Unlimited which I regeared to 4.88 recently. Also no problems at all.
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post #15 of 197 Old 08-30-2009, 07:55 AM
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Quote:
Originally Posted by floridajpr View Post
I've been running Royal Purple synthetic in my diffs since 2006 when I lifted my Heep and I have driven many road miles and used my Heep on the farm, pulling my ATV trailer, boats, Hunting and fishing, pulling other stuck vehicles out and offroading in the mud here in Florida all the way to mountains in North Carolina. I have yet to have any problems. Synthetic oil is suppose to have a higher boiling point than regular Dino oil, so why would it overheat faster?
But have you taken the rear apart and had it inspected to see if there is a issue? Example had a buddy drive a celica with only one quart of oil in it. Drove it that way for years(yes) He would claim no issues. I began to believe him. But one day I convinced him to change the oil in it and when we puled the plug a bunch of shiny metal came out. So if he had never looked he would still be going around saying
Quote:
I have yet to have any problems.
But in reality he was having problems, just to ignorant to check it.
But not saying your right or wrong. I am just pointing out a flaw I see in someones statements. Now if you have done a though inspection please add that to the post. I am trained in Aircraft hydraulics and we run a patch test ever so many hours. It test the metal content of the fluid. Easy done draw out a set amount of fluid from the diff after running it a set amount of miles. Drain the fluid though a white coffee filter and then drain though some alcohol or other clear solvent. Mostly to get rid of the colored oil and leave only the metal particulates. The darker gray the more the metal.
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