Strange Gear OIl Observation

[Jim Allen]

I had a limited slip installed by Auburn Gear (at Auburn Gear's test lab). They recommend a mineral gear oil with their limited slip because they have learned that synthetics may cause a decrease of bias ratio from the increased lubricity. Because I'm doing a test of their unit, I'm going to play their game... at least until I'm done testing. What interested me was oil temps. Let me outline this for you for your interest, consideration and commentary.

I can measure oil temp in the diff. Auburn is about 80 miles from me. I monitored oil temp at steady speeds, recording the point at which it stabilized. In general, I have learned that the higher the speed, the higher the temp. I drove at 55, 65 and 70 mph. Here are the results.

Trip Out
Open DIff
Oil: 75W140 RP Max Gear
Ambient Temp: 22F
Average Temp @ 55 mph: 122F
Average Temp @ 65 mph: 132F
Average Temp @ 70 mph: 143F

Trip Back
Auburn Gear HP Series
Oil: Chevron RPM 80W90 Universal Gear Lubricant
Ambient Temp: 30F
Average Temp @ 55 mph: 120F
Average Temp @ 65 mph: 128F
Average Temp @ 70 mph: 130F

FYI: It took 5.4 miles at 22F ambient to bring the oil to 100F (from about 40F in the garage).

I kinda expected to see slightly higher temps, both from break-in of the new carrier bearings (which were installed at a slightly higher preload than the original) and the Chevron mineral gear oil. Not sure if the slight increase in ambient temp would have mattered.

 

[INDYMAC]

Thanks for the report Jim. It sort of reminds me of the old test you did with LE607 SAE90 in your old farm truck. I like these real world tests. Keep up the great work!

 

[mechtech2]

New parts means new alignments.
It changes everything and makes the oil temp comparison invalid.

 

[dailydriver]

MOST of the domestic limited slip manufacturers require/suggest mineral based gear oils (YES, even the Torsen/worm gear type diffs), for basically the same reasons Auburn stated to you.

I don't know what the Euro/Nippon manufacturers require/suggest in their units though (Quaife, AutoTech, Kaaz, Carbonetics, etc.).

 

[Fat80y]

Jim,

I note you ran different weights for your trips. 140 out and 90 back. I assume because the 140 is thicker more friction and therefore more heat is created?

 

[shanneba]

dailydriver-
When I bought my Quaife Diff, Byrds Auto in the UK suggested Mobil VS600 75w-90. I have been running Red Line 75w-90 NS.

From their reply:
On the subject of lubes, Quaife say any conventional gear oil, but do not use LSD oil. The friction modifiers in some of those oils tend to limit the bias ratio because they are too slippery, and the diff needs a bit of gear friction to work properly. We use Mobil VS600 75W-90 Synthetic. Any lube of that grade will be okay.

 

[Jim 5]

Interesting.

Could this be attributable to something like wind? In my neck of the woods, I'm bucking at least a 30 MPH headwind if I'm going west and have the same tailwind when going back east. It makes a measurable difference in MPG.

Next time you're under your truck, I'd love to see a snapshot of your diff's temp sender.

 

[Jim Allen]

Originally Posted By: mechtech2
New parts means new alignments.
It changes everything and makes the oil temp comparison invalid.


Yeah, I agree, even though backlash and bearing preload was pretty close to what we took out (though we added a few thou to the preload on assembly). It was just one of those things where you expect to see one thing and you get another. And, yeah, the difference in fluid friction from a 140 to a 90 may account for some of it too. At a cool 130-140Foperating temp, that 140, even though it's a syn, is running at a somewhat higher viscosity than the 90 at the same temp.

Not too windy yesterday and I was running against what there was on the trip home with the cooler temps. I ran 1mpg less on the trip home than the trip there.

Well, no matter what, I can lay two strips of rubber now instead of one. The truck did a pretty impressive, two-tire, white-smoking burnout in the parking lot there at Auburn, with a rather gleeful engineer in the right seat.!

 

[Johnny]

Jim, wish I was your next door neighbor. You really do some neat things with your testing for different manufactures.

My thought on gear oils:

For the normal everyday driver like most of us, no more is needed than a well formulated mineral gear. Only exception might be in extremely cold conditions where a synthetic 75W might give better lubrication on those very, very cold starts.

For high performance racing applications, or in the over the road 18-wheelers that carry very heavy loads at constant speed, a good synthetic is better for the high temp conditions.

Until I moved to WI 20-years ago, I could tell no difference in the performance between a 80W-90 mineral gear oil and a 75W-90 synthetic gear oil.

Keep us posted on your final results.

 

[Ursae_Majoris]

Originally Posted By: dailydriver
MOST of the domestic limited slip manufacturers require/suggest mineral based gear oils (YES, even the Torsen/worm gear type diffs), for basically the same reasons Auburn stated to you.

I don't know what the Euro/Nippon manufacturers require/suggest in their units though (Quaife, AutoTech, Kaaz, Carbonetics, etc.).

I know for a fact that Toyota Tacoma LSDs do not like synthetic gear lubes, they bind even with double the LSD additive. http://www.toyotanation.com/forum/showthread.php?t=120918

On another hand, I used Valvoline 80w-90 Durablend in my Isuzu (with half a tub of GM-recommended LSD additive), and it is working just fine.

 

[Johnny]

Originally Posted By: Ursae_Majoris
Originally Posted By: dailydriver
MOST of the domestic limited slip manufacturers require/suggest mineral based gear oils (YES, even the Torsen/worm gear type diffs), for basically the same reasons Auburn stated to you.

I don't know what the Euro/Nippon manufacturers require/suggest in their units though (Quaife, AutoTech, Kaaz, Carbonetics, etc.).

I know for a fact that Toyota Tacoma LSDs do not like synthetic gear lubes, they bind even with double the LSD additive. http://www.toyotanation.com/forum/showthread.php?t=120918

On another hand, I used Valvoline 80w-90 Durablend in my Isuzu (with half a tub of GM-recommended LSD additive), and it is working just fine.


Do you have any trouble with 80W-90 up in Alaska during winter?

 

[Jim 5]

FWIW

The G80 Eaton locker in my previous truck (a chev avalanche) did just fine on 75w-90 synthetic gear oil. It has clutch packs.

I haven't seen the specs on the locking diff in my Sierra 2500, but I assume it's a variant of the G80 that's in the half tons. It's engagement etc. seems identical to the G80 in my previous half ton. This truck specifies the GM synthetic 75w-90 gear oil as well.

 

[Ursae_Majoris]

Originally Posted By: Johnny
Originally Posted By: Ursae_Majoris
Originally Posted By: dailydriver
MOST of the domestic limited slip manufacturers require/suggest mineral based gear oils (YES, even the Torsen/worm gear type diffs), for basically the same reasons Auburn stated to you.

I don't know what the Euro/Nippon manufacturers require/suggest in their units though (Quaife, AutoTech, Kaaz, Carbonetics, etc.).

I know for a fact that Toyota Tacoma LSDs do not like synthetic gear lubes, they bind even with double the LSD additive. http://www.toyotanation.com/forum/showthread.php?t=120918

On another hand, I used Valvoline 80w-90 Durablend in my Isuzu (with half a tub of GM-recommended LSD additive), and it is working just fine.


Do you have any trouble with 80W-90 up in Alaska during winter?


No problems. Dealer did the 30K service 3 years ago with dino Castrol 80w-90 (pour point of -30C). Never had any problems with it, but I never race my vehicles when cold. I did 60K service early, with 52K on the odometer, I was not comfortable leaving dino in for more than three years. I went with Valvoline synthetic blend because the pour point was low enough at -36C (80w-90 Durablend), vs -45C (75w-90 Synpower) and -36C for 75w-140 Synpower. For comparison, pour point for 75w-90 Castrol is -39C, almost the same as 80w-90 Durablend.

So far no problems, and we had quite a few single digits days with negative night temperatures. In another 3 years I might try the 75W-90 Synpower.

PS Differential gears showed some wear (I had to pop the cover off), but it was uniform across the teeth, with no chips. Magnetic plugs had very fine metal particles (looked like toothpaste in consistency) on them, not a whole lot.
No signs of water intrusion. Axiom breather was extended from the factory to the above the spare tire, almost a foot above the differential.

 

[mechtech2]

I glazed over the thicker lube, and concentrated on the new settings.
Thicker oil does indeed run hotter.

But why don't factories offer limited slip final drives except on a few cars? Even on low powered economy cars, they are a wonderful addition to inclement weather traction.

 

[dailydriver]

Originally Posted By: shanneba
dailydriver-
When I bought my Quaife Diff, Byrds Auto in the UK suggested Mobil VS600 75w-90. I have been running Red Line 75w-90 NS.

From their reply:
On the subject of lubes, Quaife say any conventional gear oil, but do not use LSD oil. The friction modifiers in some of those oils tend to limit the bias ratio because they are too slippery, and the diff needs a bit of gear friction to work properly. We use Mobil VS600 75W-90 Synthetic. Any lube of that grade will be okay.


This I knew. I've NEVER heard of a worm gear/Torsen type diff manufacturer EVER suggesting/requiring a gear oil with LSD friction mods already in it, nor to ever add any free-standing form of friction modifier.
Both Torsen and Detroit/Eaton True Trac will tell you that there needs to be friction not just between the gears, but between the outer gears and the case, in order to function/bias properly.
This is probably why they suggest mineral based oils as well.