Used Oil Analysis - Factory Fill Diff Fluid - Sign of Trouble?

[C66 Racing]

All,
I changed out my factory fill diff fluid with AMSOIL Severe Gear Extreme Pressure Synthetic 75w90 a few weeks ago, sampled the stock fluid and submitted it to Blackstone Labs. The fluid had 10,636 miles on it.

The results weren't good. Here is their quote:
"We normally expect to see high wear in factory fill differential sample, though these levels are a little excessive, even for that. Iron was the dominant metal and shows some serious wear at steel parts. Chrome, iron, and nickel are all alloys in steel, and should read well below average considering the short oil run. Universal averages show normal wear levels after about 29,000 miles oil use. Copper, lead, and tin show poor wearing bronze parts like a bushing. Suggest having this oil changed out if you haven't do so already and resample in 5,000 miles."

You can see the full report on this page of my dealer website:
2006 Cadillac CTS-V Used Oil Analysis Factory Fill Differential Fluid

My recommendation for those that haven't changed out the stock fluid - change it early, whether you chose AMSOIL or another fluid.

[Rich H]

Results are not unexpected for our differential. It may make sense to change out the differential oil early but the rate of wear of the metal components won't necessarily be reduced by using fresh oil. In fact, if you believe results posted for oil changeouts for the V engines using Mobil 1, the rate of metal loss to the oil is actually at its highest with the fresh oil. It may have something to do with establishing an equilibrium of heavy metals suspended or dissolved in the oil.

So what's the happy median? Change out more frequently and accelerate wear - or less often and risk contamination or degradation of the oil? Either way, if you have a poorly designed, or under-designed, diff I'm not sure the lube changeout interval is the answer.

[slothV]

Well it's obvious to me what the problem is. The calcium level is way lower than normal. And everyone knows that calcium builds strong diffs.


oh wait, that's bones....nevermind.

[z06bigbird]

Thanks for reminder. Just had my Hagen Daas, rum raisin. Best flavor out there. Better than Blue Bell.

[darkman]

Originally Posted by C66 Racing

All,
I changed out my factory fill diff fluid with AMSOIL Severe Gear Extreme Pressure Synthetic 75w90 a few weeks ago, sampled the stock fluid and submitted it to Blackstone Labs. The fluid had 10,636 miles on it.

The results weren't good. Here is their quote:
"We normally expect to see high wear in factory fill differential sample, though these levels are a little excessive, even for that. Iron was the dominant metal and shows some serious wear at steel parts. Chrome, iron, and nickel are all alloys in steel, and should read well below average considering the short oil run. Universal averages show normal wear levels
after about 29,000 miles oil use. Copper, lead, and tin show poor wearing bronze parts like a bushing. Suggest having this oil changed out if you haven't do so already and resample in 5,000 miles."

You can see the full report on this page of my dealer website:
2006 Cadillac CTS-V Used Oil Analysis Factory Fill Differential Fluid

My recommendation for those that haven't changed out the stock fluid - change it early, whether you chose AMSOIL or another fluid.

I recently changed out, and saved, my factory fill at 13,600 miles. I have ordered the oil test kit from Blackstone, but it has not arrived yet. Although, it may be awhile (weeks) I will post my analysis when it arrives.

Based on the appearance of the fluid I drained, I believe it should have been changed it much sooner. Unless and until I see evidence that the rate of contamination has subsided (such as an oil analysis or visual inspection) I intend to change the fluid with each oil change.

[P-Funk]

Originally Posted by z06bigbird

Better than Blue Bell.

[darkman]

Originally Posted by P-Funk

Agree.

[CIWS]

Well just judging from my own personal experience, somewhere around 12-14K miles of use the diff starts making the growling sound with low speed turns (reference the TSB) and the car goes back to the dealership to change the fluid and relube it. That's where mine is this morning and one of the things they are scheduled to do to it. I have 31,771 on the car and this will be the third instance of fresh fluid it will see. That is if the dealership doesn't push for a diff replacement.

[darkman]

Originally Posted by CIWS

Well just judging from my own personal experience, somewhere around 12-14K miles of use the diff starts making the growling sound with low speed turns (reference the TSB) and the car goes back to the dealership to change the fluid and relube it. That's where mine is this morning and one of the things they are scheduled to do to it. I have 31,771 on the car and this will be the third instance of fresh fluid it will see. That is if the dealership doesn't push for a diff replacement.

I do not claim to know with certainty, but I think your experience indicates that even if the fluid is capable of adequate lubrication beyond 12-14k the friction coefficient is no longer suitable for the requirements of this particular limited-slip differential. Stated differently, you differential needs a fresh dose of friction modifier at the very least. Naturally, a fresh fill is the best way to reestablish the proper friction coefficient.

[Rich H]

Originally Posted by darkman

I do not claim to know with certainty, but I think your experience indicates that even if the fluid is capable of adequate lubrication beyond 12-14k the friction coefficient is no longer suitable for the requirements of this particular limited-slip differential. Stated differently, you differential needs a fresh dose of friction modifier at the very least. Naturally, a fresh fill is the best way to reestablish the proper friction coefficient.

It would be valuable to see if the lab measured any of these characteristics - although I doubt the friction coefficient is a standard test. I used ATF with friction modifier in a manual tranny on another vehicle and it was shifting fine after 90,000 miles. I changed it simply because I dropped the tranny for a clutch job.

[CIWS]

Car is back after the change and all is quiet again. However odds are somewhere between 10-14K and it will be back.

[darkman]

Originally Posted by Rich H

It would be valuable to see if the lab measured any of these characteristics - although I doubt the friction coefficient is a standard test. I used ATF with friction modifier in a manual tranny on another vehicle and it was shifting fine after 90,000 miles. I changed it simply because I dropped the tranny for a clutch job.

There is a standard test ("chatter test") for the friction coeffecient required by limited slip differentials that is used in testing lubricants. The test, however, is not included in oil analyses because it is a physical rather than a chemical test. Additionally, this friction characteristic is only required by devices making use of internal wet clutches.

[Silver Dollar]

Fellas,

If the differential is shreading itself at ~15,000 miles, changing the oil aint gonna do squat.

By the way, mine just started groaning during slow speed turns this week. It's the first time it's made noise since I've owned it and I have 25,000 on the clock. Perhaps it's time for some friction modifier......

[darkman]

Originally Posted by Silver Dollar

If the differential is shreading itself at ~15,000 miles, changing the oil aint gonna do squat.

That is partially true, but we seem to dealing with three different problems.

One is the problem is when the differential comes apart and no one seems to know what causes that. That problem does, however, seem to be limited to 2004 and some 2005 units based on what I read in this forum.

The second problem involves chattering. This condition is the inability of the limited clutches to engage and disengage properly and is apparently caused by the level of friction coeffecient. This is not a part failure, does not represent permanent damage, and can be corrected with a fluid change and/or soaking the clutch packs in friction modifier.

The third problem is noisey operation (the howl). The cause of this problem is neither singular nor clear cut. First, it is somewhat inherent in relative size of the internal gears and the small case. Second, it reportedly gets louder with age, which is not atypical with gear sets. Eventually, the louder howl can be caused by parts wearing to the point where they are longer within operational tolerances. For example bushings or bearings are no longer within serveable limits, the gears have ridging, rippling, pitting, or spalling, the lash/back lash between the ring and pinion are out of tolerance. In other words the wearing parts "wear out." Finally, in the case of the CTS-V differentials there is significant evidence that this third condition can be accelerated by episodes of wheel hop.

[Silver Dollar]

^^ all of that makes sense to me. Good summary.