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Unread 09-28-2011, 11:28 PM   #1
joe002
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Short test with conventional gear lube and Valvoline Synthetic

I had some work done on my rear lockers, so after they were finished the dealership filled the axle with the stock Chrysler dino oil. I ran it for a week and measured the temperature. It was 145ºF when I got to work (back roads, slightly down hill), and 162ºF when I returned home (same roads, slightly up hill, and higher ambient temp). For 5 days the temps were within 1 degree. I changed out the lube with Valvoline Synthetic 75w90 and with my drive to work it was now 137ºF and my return home it was 148ºF.

I figured the synthetic was better (it’s higher than GL-5 because it’s also MT-1 and SAE J2360), but it was nice to see that it does keep the axle components cooler.

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Unread 09-28-2011, 11:33 PM   #2
tjkj2002
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Quote:
Originally Posted by joe002 View Post
I had some work done on my rear lockers, so after they were finished the dealership filled the axle with the stock Chrysler dino oil. I ran it for a week and measured the temperature. It was 145ºF when I got to work (back roads, slightly down hill), and 162ºF when I returned home (same roads, slightly up hill, and higher ambient temp). For 5 days the temps were within 1 degree. I changed out the lube with Valvoline Synthetic 75w90 and with my drive to work it was now 137ºF and my return home it was 148ºF.

I figured the synthetic was better (it’s higher than GL-5 because it’s also MT-1 and SAE J2360), but it was nice to see that it does keep the axle components cooler.
Actually it's doing the exact opposite,the syn gear oil is not transfering the heat from the diff internals to the diff housing as effectively as dino gear oil was,hence the cooler diff housing temps.Your cooking the internals more with syn.

Auto makers admit that syn gear oil is not the best when the OCI for diffs have dropped down to as low as 12,000 mile intervals when in the old days of running dino 80w-90 you basically never changed the gear oil.
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Unread 09-28-2011, 11:40 PM   #3
joe002
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Originally Posted by tjkj2002 View Post
Actually it's doing the exact opposite,the syn gear oil is not transfering the heat from the diff internals to the diff housing as effectively as dino gear oil was...
So the metal housing being cooler means the internal gears are hotter? I didn’t measure the actual temp of the oil, only the metal housing, the flange, etc. - all cooler...

Also note the temperature of my diff is hotter at the bottom (where the oil is) then at the top (where the oil isn't). I recorded the hottest temp I could find...
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Unread 09-29-2011, 01:29 AM   #4
ronjenx
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Quote:
Originally Posted by joe002 View Post
So the metal housing being cooler means the internal gears are hotter? I didn’t measure the actual temp of the oil, only the metal housing, the flange, etc. - all cooler...

Also note the temperature of my diff is hotter at the bottom (where the oil is) then at the top (where the oil isn't). I recorded the hottest temp I could find...
I have found the highest temps to be at the point the pinion portion of the housing meets the "pumpkin" portion of the housing. That's where the heat transfer is most direct, and less dependent on having to go through the fluid.

Regarding the post saying synthetic oil cooks the internals more, I have read lots of claims on both sides of that issue. It's typical of all the "this versus that" debates. Having read reports on both sides that were backed up by scientific sounding evidence, I can't really tell which is true.
However....
I can relate my own experience. I've put many hundreds of thousands of miles on quite a few differentials. Some had regular oil, most had synthetic oil. Never had one go bad in any way. None showed any signs of the gears or bearings being "cooked".

My conclusion? You are good either way. (Make sure it's GL-5 or equivalent, and the correct viscosity.)
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Unread 09-29-2011, 11:19 AM   #5
joe002
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Originally Posted by ronjenx View Post
I have found the highest temps to be at the point the pinion portion of the housing meets the "pumpkin" portion of the housing. That's where the heat transfer is most direct, and less dependent on having to go through the fluid.

Regarding the post saying synthetic oil cooks the internals more, I have read lots of claims on both sides of that issue. It's typical of all the "this versus that" debates. Having read reports on both sides that were backed up by scientific sounding evidence, I can't really tell which is true.
However....
I can relate my own experience. I've put many hundreds of thousands of miles on quite a few differentials. Some had regular oil, most had synthetic oil. Never had one go bad in any way. None showed any signs of the gears or bearings being "cooked".

My conclusion? You are good either way. (Make sure it's GL-5 or equivalent, and the correct viscosity.)
On mine the temp on the cover near the bottom in the middle is the same as the temp at the pinion pumpkin area you describe. On a recent trip with a number of Jeeps I measured everyone’s temps, and found that some with heavy metal armor and skids have a lower reading on the cover, but yes, the pinion area was always the temperature one would expect to see (as a side note: at freeway speeds, the temperature of my 5.38s ran about 20º hotter than the stocker TJ gears on the freeway as the 5.38s turn a lot more than the stock gears so one would expect a little more heat).

I also have seen a lot of debate about the benefits/drawbacks of synthetic verses regular gear oil - especially on this forum. That’s one reason I posted my simple/short notes as it appears to show that my rear axle at all measurable metal points runs at a lower temperature with the Valvoline Synthetic verses the conventional oil they put in a the dealership.

I agree that you need to use the correct viscosity for the way you drive your Jeep (tow or not), and that you need a GL-5. I like that Valvoline also meets or exceeds MT-1 and SAE J2360.
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Unread 10-02-2013, 06:52 AM   #6
94beachxj
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Quote:
Originally Posted by tjkj2002 View Post
Actually it's doing the exact opposite,the syn gear oil is not transfering the heat from the diff internals to the diff housing as effectively as dino gear oil was,hence the cooler diff housing temps.Your cooking the internals more with syn.

Auto makers admit that syn gear oil is not the best when the OCI for diffs have dropped down to as low as 12,000 mile intervals when in the old days of running dino 80w-90 you basically never changed the gear oil.

One problem here.......2prob's.........Most lockers such as the Auburn gear apps that I use, require normal dino Motorcraft fluid strickly!

But in my stock Jeep Liberty the owners manuel says Syn Lube only!

I added a locker to my old 94 Cherokee a few yrs ago and I thought syn or Lucas would do the trick.....WRONG! After Auburn reps told me the reason why I had chatter on right hand turns, I switched to Motorcraft fluids.

So if its stock stick to the book, if not call the company you purchased the locker from imo.
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Unread 10-02-2013, 08:33 AM   #7
Maertz
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Quote:
Originally Posted by tjkj2002 View Post

Actually it's doing the exact opposite,the syn gear oil is not transfering the heat from the diff internals to the diff housing as effectively as dino gear oil was,hence the cooler diff housing temps.Your cooking the internals more with syn.

Auto makers admit that syn gear oil is not the best when the OCI for diffs have dropped down to as low as 12,000 mile intervals when in the old days of running dino 80w-90 you basically never changed the gear oil.
This x2 i just use standard gear oil
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Unread 10-02-2013, 10:15 AM   #8
jwmbishop
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Quote:
Originally Posted by joe002 View Post
So the metal housing being cooler means the internal gears are hotter? I didn’t measure the actual temp of the oil, only the metal housing, the flange, etc. - all cooler...

Also note the temperature of my diff is hotter at the bottom (where the oil is) then at the top (where the oil isn't). I recorded the hottest temp I could find...
FAR too many variables for your test to be conclusive.

The gear tooth contact COULD be making more heat, with the oil carrying less to the housing - thus showing a lower housing temp. Could be making LESS heat but but carrying more and STILL be under the thermal transfers of the other oil! The two have very different splash and cling characteristics.

Picture your engine for example. With no load runs right at 180 - but climb a hill and the temp wants to go up to 210 but the system maintains 180. Same coolant! Different heat load - but more heat coming out of the radiator airflow.

We did compare with our quick change Hildebrant a few years back. AFter a 25 lap warm up we pulled the gears and immediately read them with a pyrometer right at the gear. Although the gear temp was within a few degrees (synth slightly cooler) - the synth oil was MUCH cooler and the housing was a bit warmer (had to use gloves to touch with synth but not with dino)- I think it transfers heat to the housing better (more cling on the stationary housing surface than on the rotating gears).

I think the bottom line is that although both provide good lubricity to the teeth - synth will stay "good" through a lot more heat cycles than dino giving longevity in lube quality. If you change often - dino is more economical. If you change seldom synth will provide better protection.
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