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

[Rich H]

But the question still remains - does a lube change every 10,000 miles really increase the overall service life. Mine just started to whine at ~26,000 miles. I haven't changed fluids yet and was waiting to see if I was lucky. Apparently not. If I change the fluid now it may run quiet for a while but the damage is likely done and the tolerances will just continue to increase regardless of the new vs old fluid. This differential was designed to self destruct when placed in the drivetrain with our LS6 or LS2 engines whether you are hard on it or not.

[darkman]

Originally Posted by Rich H

But the question still remains - does a lube change every 10,000 miles really increase the overall service life. Mine just started to whine at ~26,000 miles. I haven't changed fluids yet and was waiting to see if I was lucky. Apparently not. If I change the fluid now it may run quiet for a while but the damage is likely done and the tolerances will just continue to increase regardless of the new vs old fluid. This differential was designed to self destruct when placed in the drivetrain with our LS6 or LS2 engines whether you are hard on it or not.

Your correct that we do not have conclusive evidence that frequent fluid changes will extend the service lives of THESE differentials. That would presumably require: (1) a number units subjected to frequent changes; (2) another set units operated without frequent changes; and (3) a comparison of resutling service lives or a measurement of accumualted wear and tear.

What we do have, however, is substantial evidence that fluid changes done both early and often seems to coinicide with better results in terms of service life for a number of individuals in this forum. We also know that contaminated fluid accelerates wear on bushings, bearings, and gear sets.

Changing fluid in a unit with 26K may be "too little, too late," but it can't hurt.

[CTSV_Rob]

Good write up dm, makes sense to me.

I only have 6K on my diff and I am planning to change the fluid. Some are concerned with warranty but I'm not convinced the GM lubricants are as good as some of the after market versions. Some people are hung up on specs but after hearing that GM realized this diff would not handle the power and they signed it off anyways would make me question whether the fluid meet the specs they outlined for the diff.

It has been my experience in the past that the after market fluids were typically better then the orginal GM versions. GM is a large company and being a large company they will try to cut corners where ever possible. With this being said it wouldn't be a stretch to say they have a chance to put $5 dollar a quart or $10 a quart fluid the bean counters will pick the $5 version. Nothing against GM but they are a large company and the bean counters have more say then any of us on the outside would like. I have heard rumor this is why we have a 6 bolt wheel on the V's for example.

With this said I believe there are better fluids then the GM versions. I have only heard good about the Amsoil but since C66 reps the fluid I would rather hear from someone that doesn't. I don't mean to say I don't trust what you say C66 but since you rep them you might be a little biased.

I am currently planning to put the fluid in my car (Amsoil MaxDiff 75W90) but I sure wish there was more information/tests with this fluid and this rear.

If they won't warranty the diff over fluid then I think they won't anyways because of the power adders I have on the car. Need to find a dealer that believes in customer satisfaction then I should be good to go.

[darkman]

I think we fully vented the brand vs. brand issue in an earlier thread and I am not incliined to revisit that subject now. I do not know whether GM, or any other brand for that matter, actually bottles the fluid they claim to bottle. I think GMs stuff comes from an outside vendor.

I do believe, however, the facts we seem to know at this time fully support frequent fluid changes with whatever brand folks prefer.

[CTSV_Rob]

It wasn't my intension to revisit the fluids but just a comment. I'm sure your right, I doubt GM makes the oil themselves. For example, GM doesn't make Silicon wafers (anymore but they used to at Delco in Indiana, Saw it for myself) they buy the Navigation systems.

I agree with your comment about frequent fluid changes however I believe there are better fluids.

[CIWS]

The question with any fluid put into the car is if it meets minimum GM spec, no matter how good it actually is. We should all know by now that a dealership / Cadillac could attempt to deny warranty work if you use a fluid or oil that does not meet their listed spec.


My replacing of the diff fluid has been soley related to the "growl" experienced with slow speed turns like in the parking lot. It has no whine and no fluid has been replaced in my case due to a whine, only the growl.

[Rich H]

Originally Posted by CIWS

The question with any fluid put into the car is if it meets minimum GM spec, no matter how good it actually is. We should all know by now that a dealership / Cadillac could attempt to deny warranty work if you use a fluid or oil that does not meet their listed spec.


My replacing of the diff fluid has been soley related to the "growl" experienced with slow speed turns like in the parking lot. It has no whine and no fluid has been replaced in my case due to a whine, only the growl.

Then that would seem to indicate that your friction modifier is degrading for some reason since the growl is likely related to the limited slip differential not having the correct friction coefficient. If you have no whine the tolerances are probably still good for the mechanical gears and I assume you ARE adding the correct friction modifier every time you change the fluid. By the way, have you had the back seats down to confirm you have no whine? Mine rear sounds fine until I lower the back seats.

[C66 Racing]

Originally Posted by darkman

What we do have, however, is substantial evidence that fluid changes done both early and often seems to coinicide with better results in terms of service life for a number of individuals in this forum. We also know that contaminated fluid accelerates wear on bushings, bearings, and gear sets.

I appreciate the healthy discussion this thread has generated. Darkman's response above summarizes my view's well.

But, and I understand Rob's skepticism, I do feel that good aftermarket fluids do offer improved wear resistance. This, I feel, will reduce the amount of contaminates floating in the diff fluid which I can only believe would further reduce wear on parts like the bushings and bearings (which based on my sample don't appear to be holding up well).

[Rich H]

Originally Posted by C66 Racing

I appreciate the healthy discussion this thread has generated. Darkman's response above summarizes my view's well.

But, and I understand Rob's skepticism, I do feel that good aftermarket fluids do offer improved wear resistance. This, I feel, will reduce the amount of contaminates floating in the diff fluid which I can only believe would further reduce wear on parts like the bushings and bearings (which based on my sample don't appear to be holding up well).

But as Darkman also states, there is no direct evidence that changing the fluids regularly significantly lengthens the service life of THIS differential.

[darkman]

Originally Posted by Rich H

But as Darkman also states, there is no direct evidence that changing the fluids regularly significantly lengthens the service life of THIS differential.

I did NOT say there is no DIRECT evidence, I said there is no CONCLUSIVE evidence owing to the absence of a controlled comparison study.

We have lots of DIRECT evidence that infrequent fluid changes will shorten the life of these differentials such as: (a) the Blackstone oil analysis provided by C66 Racing; (b) visual inspection of my fluid which I found to be heavily contaminated (oil analysis pending) (c) the remarks by CIWS concerning the indicated service life of his fluid in terms of friction coefficiency; and (d) reports by other forum members concerning their experience with early and frequent changes.

The evidence here is no more ambiguous that the maintenance schedule that we are addressing in the first place. Specifically, GM says to change the fluid every 50,000 miles unless the car is "used for high performance operation" for which the frequency drops to every 3,000 miles. Thus, we are dealing with a manufacturer's instructed frequency that ranges from 3,000 to 50,000 miles tied to the ambigous term "high performance operation."

I am not sure what degree of certainty you are seeking. Afterall, we are merely suggesting that the prudent course of action appears to be changing the fluid more often. (closer to 3,000 miles than to 50,000 miles) This is not a "life or death" decision requiring absolute certainty.

[CIWS]

Originally Posted by Rich H

If you have no whine the tolerances are probably still good for the mechanical gears and I assume you ARE adding the correct friction modifier every time you change the fluid. By the way, have you had the back seats down to confirm you have no whine? Mine rear sounds fine until I lower the back seats.

Each time it's been performed by the dealership. Now I can only assume (cough) it's being done correctly. If it were Lindsay I would have complete confidence in this, but unfortunately it's not.

I have run with a single back seat lowered when recording the exhaust note. But I can always do it again and keep the mic internal to the trunk to see if it picks up anything.

[Rich H]

Originally Posted by darkman

I did NOT say there is no DIRECT evidence, I said there is no CONCLUSIVE evidence owing to the absence of a controlled comparison study.

We have lots of DIRECT evidence that infrequent fluid changes will shorten the life of these differentials such as: (a) the Blackstone oil analysis provided by C66 Racing; (b) visual inspection of my fluid which I found to be heavily contaminated (oil analysis pending) (c) the remarks by CIWS concerning the indicated service life of his fluid in terms of friction coefficiency; and (d) reports by other forum members concerning their experience with early and frequent changes.

The evidence here is no more ambiguous that the maintenance schedule that we are addressing in the first place. Specifically, GM says to change the fluid every 50,000 miles unless the car is "used for high performance operation" for which the frequency drops to every 3,000 miles. Thus, we are dealing with a manufacturer's instructed frequency that ranges from 3,000 to 50,000 miles tied to the ambigous term "high performance operation."

I am not sure what degree of certainty you are seeking. Afterall, we are merely suggesting that the prudent course of action appears to be changing the fluid more often. (closer to 3,000 miles than to 50,000 miles) This is not a "life or death" decision requiring absolute certainty.

DIRECT, CONCLUSIVE, UNDENIABLE, WHATEVER

The point is that others have noticed a short term reduction in noise after a fluid change but the noise always returns if it was already present. Some notice the noise immediately after installation of their "new" rear-end, some must wait a considerable time before onset. I don't think we know why this is. If the noise were related to gradual breakdown of the metal components (gears and bearings) due to mechanical overload why is there such a drastic difference in reported "time to whine" or "time to failure". I am not the type that goes out and tries to blow-out my rear-end, but I sure don't baby it either.

I've scheduled an appointment with my dealer on Monday so he can do some diagnostics on mine. I told him that nothing short of replacement with the latest part is acceptable- so we shall see. Then I will do whatever it takes to keep this one in top shape. And if that requires changing the fluid every 10,000 miles or less I'll do it. And then if it lasts 50,000 miles before whining or breakdown that's a good enough controlled evaluation for me to judge that the service life has been signifcantly extended.

[CTSV_Rob]

I will be changing my fluid out soon with the MaxDiff. If I decide to send the fluid in for eval then where do I send it and what does this typically cost?

Interesting thread and everyone has made some interesting points.

[Rich H]

Originally Posted by CTSV_Rob

I will be changing my fluid out soon with the MaxDiff. If I decide to send the fluid in for eval then where do I send it and what does this typically cost?

Interesting thread and everyone has made some interesting points.

Amsoil offers a prepaid oil analysis kit for about $25 - see attached link. http://www.amsoil.com/storefront/oai.aspx

[DILLIGAF]

Don't waste your money guys.Stock diff,one lube change at 500 miles,30,000+ maggied miles and quiet as a mouse.I'll change it at 50,000 maybe