Transfer Case Lubricant Selection
By David Newton
Preface:
Many times the question is asked as to what fluid is appropriate for use in the GM transfer cases in the four-wheel drive vehicles bounded by the 2500HD and 3500HD series. The following is an attempt to inform all who have intent to maintain their vehicles of the facts and logic behind the choices. There have been many discussions as to what lubricant is the “best” for this application. Let’s review what options we have, and what sources the information comes from. It is not my intent to push anyone to a conclusion, but rather to present the facts, confront the myths, and provide credible sources of information so that each individual may make an informed choice for his/her application. After all, it’s YOUR truck!
Background:
In the 2500HD and 3500HD trucks, the NV-261 and NV-263 transfer cases are utilized. Do not confuse these t-cases with the lighter duty versions in the 1500 and 1500HD trucks; they are not the same. In fact, even the 2500HD and 3500HD use slightly different versions of the 261 and 263 t-cases; however, they are similar enough to discuss them as a common group for the purpose of the topic of lubricants. GM does not make the t-cases; rather, they are purchased from what was New Venture. I say “was” in past tense, because they became part of New Process, and that in turn became part of Manga Powertrain, as of this writing. New Venture / New Process / Magna Powertrain(whatever you want to call them) are the OEM. GM is the seller/warrantor.
Detailed t-case design notes:
The 261,263 t-cases have been magnesium-cased, but some info exists that they may now be aluminum-cased. Case material has no influence on lubricant selection, for this topic. The power transfer design is by link-plate chain, having a driving gear on the main-shaft, and a driven gear on a slave or sub-shaft. The lubrication is achieved by three methods: forced, submersion and resultant splash designs. There is a gerotor that pumps fluid into the main shaft components. The lower portion of the chain is in submersion, and carries fluid to the sub-shaft gear, via a splash effect. The selection of gear range and output for 4x4 is done by traditional shift forks. This unit’s design is fairly typical of many four wheel drive vehicles. Sizes and components are upgraded for expected severity of use. There is a separate issue with a problem called “pump rub”, but I am not intending to discuss this here, and it should be noted that “pump rub” cannot be accelerated, nor prevented, by lubricant choice selection. It is a mechanical design issue, not a lubricant issue.
Lubricant Options:
Lubricants can be divided into two main options for this application; the specified fluids (automatic transmission fluid, i.e.ATF) and the alternative fluid (engine oil). The ATF can be sub-divided into different types (DEXRON III-h or DEXRON VI). The engine oil is typified by API 5w-30 grade oil. While it’s possible to use other fluids such as GL rated gear lubes, light grease, and such, they are not good alternatives for this application. The main discussion is between ATF and 5w-30 engine oil. Let’s looks at the individual choices.
ATF is specified by both the OEM (NV/NP) and seller/warrantor (GM). The reason is because that’s what GM requested the t-case to perform with, and that’s how it is tested at NV. Now that DEX VI has replaced DEX III, GM is specifying DEX VI. They are dissimilar enough to warrant certain precautions in some applications such as the Allison transmission, yet similar enough per GM to warrant its use throughout the GM product line. It is reasonable to expect that NV and GM collaborated on the design, development, and manufacture of the t-case, in all aspects. While not published outwardly, it’s common practice to expect full testing and FMEA (failure mode/effect analysis) criteria in large companies such as these. I have personally spoken with the product development/engineering services at both NV (at Syracuse) and GM (in Detroit), and the correct fluid specification is ATF, meeting either (former) DEX III or (current) DEX VI qualifications depending upon vehicle year. This is after numerous tests including wear analysis tear down, fluid property comparisons, and GM preferences for product viability and availability. GM has very good access to both engine oil and ATF; they chose ATF for the t-case based upon positive results for the preferred criteria they sought. That does not mean that ATF is perfect; it reflects the choice that GM made in that ATF best fit all the criteria as prioritized.
Engine oil has been touted as a replacement fluid for ATF in this application*. This suggestion comes from a noted “expert” in his field. Mike Weinberg is the president of Rockland Standard Gear, a re-manufacturer of power-train components; he has an extensive and impressive employment history. He wrote an article for Transmission Digest describing the detailed operation and issues with the 261/263 cases. In that article, he noted that RSG often found low or non-existent levels of fluid in the t-case upon teardown. He theorized that the fluid was over-heating and escaping through the vent. He specifically stated to use 5w-30 engine oil for this application, although he provided no data to back this up. Further, Weinberg suggested over-filling the t-case by 50%, adding one quart above capacity. In analysis, it’s important to note that he has actually made two distinct suggestions in one article; either could be implemented individually, or together. The article has no technical data, no references to industry studies, and no mention of the two opposing fluids’ properties.
*It is important to note that save for this one article from Rockland, I cannot find any other
source that makes this same claim.
I was able to contact Mr. Weinberg directly, and got information from him. He specifically cited his credentials in the industry, which are notable. He did indicate that he is not a petroleum engineer. He stated that he didn’t seek out specific information regarding the different lubricant properties for consideration in making his decision. He did mention the great success his company has had regarding the long-standing use of engine oil in the t-cases. Here is a direct quote from his reply:
“We have been using 5W30 motor oil in mechanically shifted transfer cases instead of ATF for over 30 years. We have seen hundreds of units that have over 100K miles on them running on 5W30 with zero negative outcomes”
However, he also mentioned that there is a 2% return warranty rate on their work. It was not a specific statement as to whether it was transmission or t-case related. So it would be unfair to claim that 5w-30 resulted in certain t-case failures, but it is fair to say that at least some of the time, 5w-30 may have contributed to failures. It is unknown if some t-case fluid levels were neglected, and having 5w-30 in them, resulted in failures attributed to the fluid.
Other Sources of Information:
Other industry competitors to Rockland do not support the use of any fluids other than what is required by the OEM. Specifically, Jasper Engines is also a renowned re-manufacturer. After speaking with their tech support analyst, they recommend use of OEM fluids, and will only warrant their work and products with fluid applications in line with OEM specifications. They had heard of the topic, and discouraged the use of engine oil because it had not been tested nor its performance validated.
Although some may exist, I could not find references to a specific re-manufacturer’s council regarding transfer cases. However, I did find the Production Engine Remanufacturers Association (PERA); they have no comment other than to echo those that are in line with the OEM fluid specifications. Since many re-manufacturers do engines, transmissions, differentials, and t-cases, it’s reasonable to assume the principles apply with consistency.
Transmission Digest, the trade magazine where the article appeared, has no comment other than to refer to the author of the article, Mr. Weinberg. They have no technical staff to validate articles; they simply edit and publish topics from industry contributors.
Other research includes advice from noted active and retired lubricant engineers and tribologists. Several I have spoken with suggest that staying with OEM specs can never be a bad thing, although there is always room for exceptions. However, care should be used before making such alternate selections. ATF and 5w-30 engine oil do not typically share the same viscosity properties; typical ATF has a viscosity of around 7.0 cSt at 100 degC whereas a 5W-30 engine oil is more like 10.5 cSt at 100 degC, so ATF is more like an SAE 15 weight. This would indicate that ATF would flow better into the link plates of the chain. In fact, a 5w-20 would be more like ATF, to mimic the grade of the ATF. NOACK values in a 5w-30 are around 13-15, where NOACK in ATF it is about 18-20. The difference is substantial enough to be considered non-empathetic; it is not reasonably interchangeable.
Details of lubricant characteristics:
The original comment from Weinberg suggests that the 5w-30 was selected for a higher resistance to evaporation. This is probably a good thing to have. But there are many good solutions to finding a fluid that resists evaporation more so than a traditional ATF. “Synthetic” fluids are available in many forms, groups and types. There are good synthetic fluids marketed in ATF formulas that would provide a much higher ability to withstand heat and evaporation, comparable to those of 5w-30 synthetic motor oils. It is probably not necessary to seek out a different type of fluid (motor oil) when an upgraded fluid base stock of ATF can provide the same results, and do it within the confines of the base lubricant properties.
While people would rightly point out that there are differences between additive packages, not all of these are worthy of debate. For example, the detergent and dispersant additives highly present in engine oil mean little to the t-case, because these are to help control soot, insolubles, etc. Since these combustion byproducts are not present in a t-case, the engine oil has no advantage in this regard.
Common sense questions arise from reading the article. First, no information was presented that gave indication of maintenance history for the t-cases involved in helping Weinberg making his determination. We do not know if the t-cases were neglected; perhaps fluid checks and changes were not performed adequately. Second, we don’t know the operating environment that the t-cases were present in, before removal. In a nutshell, nowhere does the OEM or GM indicate these t-cases are “fill and forget” equipment. They must be maintained, including proper fluids and levels. To let a t-case get so low on fluid that damage occurs is not the fault of the lubricant; it’s the fault of the owner for poor/neglected maintenance. If extreme low levels of 5w-30 lubricant were to occur, it’s likely the same disagreeable results would result.
Further, it’s reasonable to think that the OEM and GM considered the operating environment, including temps, angles, fluid levels, wear patterns, gear and bearing loads, etc. After all this, they specified ATF. It is not as though ATF is not capable. Engine oil may work, but it may not work as the designers intended.
Over-filling the t-case is an answer to a question that probably should have been addressed differently. If one maintains the levels properly, there should be no reason to over-fill the t-case. In fact, there are times when over-filling gear cases in general, creates other problems such as aeration, foaming, higher internal pressures, etc. If your fluid level is kept at “normal” design levels with proper maintenance, you should have no need to over-fill. Over-filling the 261,263 t-cases in this scenario has not shown any detrimental effects, but neither has it shown any advantages. There may be proof at the developmental level (OEM) one way or another, but field results don’t seem to reflect cause for concern. Overfilling is likely a precaution that adds cost, but little else.
5w-30 engine oil does have a higher viscosity index property, as compared to traditional ATF. In some circumstances, when used in gearboxes, it has shown marked improvements. However, this is typical of “gear-to-gear” type designs, where direct gear tooth contact is present, similar to a ring-pinion relationship. Here, thicker oil is nearly always preferred due to its viscosity and EP (extreme pressure) additives over an ATF. But even engine oil is overshadowed by true API GL rated gear lubricants in these circumstances. A common “compromise” is manual transmission fluid, which is somewhat a “hybrid” equivalent. However, we must keep in mind that the t-cases in our trucks are not of gear-to-gear design; they are link-plate chain driven. Lubrication between the plates, and to the pins, is just as important as the loading against the tooth/gear contact points.
One the most important things to understand, is that while viscosity gain can be a good thing, it can also be a bad thing. Typically, lubricants are rated at both 40 degC and 100 degC. This is because fluids never operate at just one temperature. Here’s a breakdown of DEX III and 5w-30 typical properties.
DEX III 5w-30
cSt @ 40C/104F 37 62
cSt @ 100C/212F 7.0 10.5
As you can see, while engine oil has a slight viscosity advantage at 100 degC, it is nearly 70% thicker at just above 100 degF. And is gets disproportionately even thicker below that. The problem with engine oil can be that if you don’t get your t-case hot all the time, the engine oil will not flow as well as ATF. ATF does a MUCH better job of flowing at lower temperatures. This is very important when submersion/splash lubrication is being used. So, while it’s true to say that above 200 degF 5w-30 has some advantage, other times, ATF actually flows better. By choosing 5w-30, you are trading high temp performance for low temp performance. T-cases do not always get very hot. There are many times, such as during winter, the t-case struggles to get over 50 degF! That is one time you do not want a fluid to be “thicker”. While 5w-30 works fine in a pressure fed lube system in an engine, it may not be doing that great a job when cool in a partial splash system like a t-case. And while both ATF and engine oil are available in “synthetic” products, it does not greatly change the viscosity properties of the lubricants. Upgrading from ATF to synthetic ATF is akin to moving from 5w-30 to synthetic engine oil, but the basic comparison is valid. So it is still a fair comparison for the above data.
Although not often discussed, it is appropriate to note that the new DEX VI fluid is a significant step above the old “dino” DEX III base fluids, in many regards. DEX VI has roughly twice the oxidation resistance, and twice the viscosity retention over its former fluid. DEX VI is a thinner fluid when starting out, but it stays within grade much better than traditional DEX III fluids, which drop considerably with use. DEX VI will actually be above DEX III in viscosity after some use, because the DEX III drops very steadily; yet the DEX VI holds its grade very well. And although the debate rages in regard to DEX VI usage in Allison transmissions, these upgraded properties may actually perform much better in a t-case. After all, if evaporation is the concern with a traditional DEX III, your DEX VI should last two times as long in the same operating environment. I have found no information in regard to DEX VI being tested by the OEM, but GM does warrant its use in the t-case, and is backwards compatible, per GM, although they do have conflicting documents. However, it is also important to note that DEX VI does not hold any advantage over synthetic (group VI PAO base stock) DEX III fluids. If one were to accept a “good – better – best” analogy, then you could rank the ATF fluids thusly: DEX III, DEX VI, DEX III synthetics, DEX III synthetic TES-295s.
Warranty Issues:
There are different opportunities for warranty coverage, should something happen to the t-case in the case of “normal” use. One is the OEM/Seller warranty. Another is from the lubricant marketer. Lastly, if one has rework done, then there is some expectation of coverage there are well. Let’s look at each individually.
The seller/warrantor (GM) specifies ATF at proper fluid levels. This is considered a routine maintenance item, and is the responsibility of the owner to assure proper fluids and levels are utilized. After speaking with GM, both at the corporate and dealership level, there is no assurance of warranty coverage other that what is in written form in the owner’s manual. Warranty coverage is void if non-specified fluids are used, or in conditions that do not meet with design criteria (over/under filled).
Amsoil has the following to say regarding their products and warranty:
DISCLAIMER & TECHNICAL CONCERNS
Specifications contained on this website are based on manufacturers' information and were believed accurate at the time of publication. Our recommendations apply to AMSOIL products only, as we cannot be responsible for products from other manufacturers. Always compare fluids and lubricants that were installed in the vehicle with those replacing them during service. Never install more fluid or lubricant than what is considered adequate according to gradients on dipstick or level of filler hole. Fill and drain locations are for reference only. Failure to perform adequate inspections or obtain proper resolution will limit or negate any liability toward AMSOIL INC. Models introduced midyear may not have the same specifications as those produced earlier.
Clearly Amsoil has no intent of recommending or warranting anything other than a fluid that is specified by the OEM; this is ATF. Amsoil does have products that they will warrant for use in ATF applications. This is not a comment on whether Amsoil meets OEM specs, but rather what their warranty recognizes as the proper application of their fluids to OEM specs. (I am distinguishing this because some would argue that Amsoil’s products are not tested to meet GM specs, and they’d be right. But I contend that Amsoil will warrant any failure related to lubes that they specify application for. Amsoil would warrant the t-case if you used either the “ATF” or “Torqdrive” products, as they are specified for DEX III and TES-295 applications. However, their engine oils are not specified for those same applications, therefore no warranty would be expressed or implied.)
Mobil has similar constraints:
ExxonMobil Lubricants & Petroleum Specialties Company, a division of Exxon Mobil Corporation ("ExxonMobil") provides this limited warranty to the purchasers who use Mobil brand lubricants in their vehicle.
This limited warranty covers the Mobil 1 lubricant and critical engine parts lubricated by the lubricant.
If there is equipment failure related to the Mobil brand lubricant you purchased, ExxonMobil will repair any equipment damage directly caused by a defect or malfunction of a Mobil lubricant, provided that the lubricant was selected and maintained in accordance with specifications of the original equipment manufacturer or the written instructions (which includes product packaging) of ExxonMobil.
This is specific to the Mobil 1 engine oil warranty, but all the Mobil warranties have the same general wording. Mobil will not warrant a t-case that has their engine oil in it, when the specified fluid is ATF. Mobil obviously has no intent of providing any coverage if improper fluids, or incorrect levels are used. Mobil would indeed warrant the t-case if their D/M or ATF products were used, and they do meet the full spec criteria.
In fact, it’s fair to say that all aftermarket lube companies I could find say similar things; they only warrant their products when used in accordance with OEM specs matching their application guidelines.
Rockland (RSG) says the following in their transfer case warranty: “ … Units will not be covered under warranty if they are run out of lubricant, under filled or overfilled with lubricant, or filled with the incorrect lubricant.” (Note: this is in bold type print not because I upgraded the text, but because RSG denotes it as such, to call attention to its importance). It is an interesting contradiction to the specific recommendation by Weinberg, and one that cannot (as of this writing) be reconciled. However, to be fair, given that the article was written by the RSG company president, there is a certain amount of expectation that the use of engine oil would be covered, but ONLY when used in a t-case that RSG remanufactured, and not one from any other source. RSG would not rebuild your GM backed or Jasper built transfer case, just because you used engine oil. And the corollary holds true; GM or Jasper is not going to rebuild the t-case, should you use engine oil. Each will only warrant their own work, when using the fluids that only they recommend.
Summation:
* The OEM/Warrantor specifies the use of ATF.
* The aftermarket lubricant industry as a whole recommends following OEM fluid specs.
* The remanufacturing industry, with one exception, suggests following OEM specs for fluids.
* The man who wrote the article has provided no credible sources or information to prove that motor oil is “better” than ATF in this application; he does have extensive industry experience
* Lubricant engineers imply the design characteristics should follow OEM design and development
* There is no technical evidence or industry studies available to suggest that using engine oil in lieu of ATF is harmful, nor helpful.
*The anecdotal evidence points to the fact that most failures are due to poor maintenance, and not lubricant selection.
* Engine oil is thicker at all temps; good when very hot, bad when not.
* If a longer lasting fluid is desired, that still performs within the criteria as specified by the OEM/Warrantor, a “synthetic” ATF in either DEX III or TES-295 would be a very good upgrade, without moving outside the operational boundaries of ATF.
Conclusion:
There are many people that successfully run ATF, in its many forms. It is the specified fluid, and has the full approval and warranty support of the manufacturing and lubricant industries. The failures while using ATF are likely attributed to poor maintenance routines. There are upgraded “synthetic” ATF fluids available will provide greater performance characteristics if desired.
There are many people that use basic or synthetic 5W-30 engine oil with great success as well. There are no known failures from using motor oil, although some may exist, but data is inconclusive. This may be due in part to the relative low exposure of people using these fluids, and the relatively small amount time that these alternate fluids have been in service. There is no evidence to show that this is a good or bad choice; the evidence is anecdotal.
Reality check:
There is but one fluid to use in your t-case. And that fluid choice is yours to make. The answer for you, the owner, comes from how you define your preferences, establish your goals, and maintain your vehicle. What other people choose is of no consequence. It was my intent to provide the facts, with credible resources and data. I hope that you find what you need to make your decision. All I wanted to do is set the record straight as to what information is available, where it comes from, and dispel the mythology regarding this topic.
References:
www.amsoil.com
www.gm.com
www.jasperengines.com
www.magna.com
www.merchant-automotive.com
www.mobil.com
www.pera.org
www.rsgear.com (Special thanks to Mike Weinberg)
By David Newton
Preface:
Many times the question is asked as to what fluid is appropriate for use in the GM transfer cases in the four-wheel drive vehicles bounded by the 2500HD and 3500HD series. The following is an attempt to inform all who have intent to maintain their vehicles of the facts and logic behind the choices. There have been many discussions as to what lubricant is the “best” for this application. Let’s review what options we have, and what sources the information comes from. It is not my intent to push anyone to a conclusion, but rather to present the facts, confront the myths, and provide credible sources of information so that each individual may make an informed choice for his/her application. After all, it’s YOUR truck!
Background:
In the 2500HD and 3500HD trucks, the NV-261 and NV-263 transfer cases are utilized. Do not confuse these t-cases with the lighter duty versions in the 1500 and 1500HD trucks; they are not the same. In fact, even the 2500HD and 3500HD use slightly different versions of the 261 and 263 t-cases; however, they are similar enough to discuss them as a common group for the purpose of the topic of lubricants. GM does not make the t-cases; rather, they are purchased from what was New Venture. I say “was” in past tense, because they became part of New Process, and that in turn became part of Manga Powertrain, as of this writing. New Venture / New Process / Magna Powertrain(whatever you want to call them) are the OEM. GM is the seller/warrantor.
Detailed t-case design notes:
The 261,263 t-cases have been magnesium-cased, but some info exists that they may now be aluminum-cased. Case material has no influence on lubricant selection, for this topic. The power transfer design is by link-plate chain, having a driving gear on the main-shaft, and a driven gear on a slave or sub-shaft. The lubrication is achieved by three methods: forced, submersion and resultant splash designs. There is a gerotor that pumps fluid into the main shaft components. The lower portion of the chain is in submersion, and carries fluid to the sub-shaft gear, via a splash effect. The selection of gear range and output for 4x4 is done by traditional shift forks. This unit’s design is fairly typical of many four wheel drive vehicles. Sizes and components are upgraded for expected severity of use. There is a separate issue with a problem called “pump rub”, but I am not intending to discuss this here, and it should be noted that “pump rub” cannot be accelerated, nor prevented, by lubricant choice selection. It is a mechanical design issue, not a lubricant issue.
Lubricant Options:
Lubricants can be divided into two main options for this application; the specified fluids (automatic transmission fluid, i.e.ATF) and the alternative fluid (engine oil). The ATF can be sub-divided into different types (DEXRON III-h or DEXRON VI). The engine oil is typified by API 5w-30 grade oil. While it’s possible to use other fluids such as GL rated gear lubes, light grease, and such, they are not good alternatives for this application. The main discussion is between ATF and 5w-30 engine oil. Let’s looks at the individual choices.
ATF is specified by both the OEM (NV/NP) and seller/warrantor (GM). The reason is because that’s what GM requested the t-case to perform with, and that’s how it is tested at NV. Now that DEX VI has replaced DEX III, GM is specifying DEX VI. They are dissimilar enough to warrant certain precautions in some applications such as the Allison transmission, yet similar enough per GM to warrant its use throughout the GM product line. It is reasonable to expect that NV and GM collaborated on the design, development, and manufacture of the t-case, in all aspects. While not published outwardly, it’s common practice to expect full testing and FMEA (failure mode/effect analysis) criteria in large companies such as these. I have personally spoken with the product development/engineering services at both NV (at Syracuse) and GM (in Detroit), and the correct fluid specification is ATF, meeting either (former) DEX III or (current) DEX VI qualifications depending upon vehicle year. This is after numerous tests including wear analysis tear down, fluid property comparisons, and GM preferences for product viability and availability. GM has very good access to both engine oil and ATF; they chose ATF for the t-case based upon positive results for the preferred criteria they sought. That does not mean that ATF is perfect; it reflects the choice that GM made in that ATF best fit all the criteria as prioritized.
Engine oil has been touted as a replacement fluid for ATF in this application*. This suggestion comes from a noted “expert” in his field. Mike Weinberg is the president of Rockland Standard Gear, a re-manufacturer of power-train components; he has an extensive and impressive employment history. He wrote an article for Transmission Digest describing the detailed operation and issues with the 261/263 cases. In that article, he noted that RSG often found low or non-existent levels of fluid in the t-case upon teardown. He theorized that the fluid was over-heating and escaping through the vent. He specifically stated to use 5w-30 engine oil for this application, although he provided no data to back this up. Further, Weinberg suggested over-filling the t-case by 50%, adding one quart above capacity. In analysis, it’s important to note that he has actually made two distinct suggestions in one article; either could be implemented individually, or together. The article has no technical data, no references to industry studies, and no mention of the two opposing fluids’ properties.
*It is important to note that save for this one article from Rockland, I cannot find any other
source that makes this same claim.
I was able to contact Mr. Weinberg directly, and got information from him. He specifically cited his credentials in the industry, which are notable. He did indicate that he is not a petroleum engineer. He stated that he didn’t seek out specific information regarding the different lubricant properties for consideration in making his decision. He did mention the great success his company has had regarding the long-standing use of engine oil in the t-cases. Here is a direct quote from his reply:
“We have been using 5W30 motor oil in mechanically shifted transfer cases instead of ATF for over 30 years. We have seen hundreds of units that have over 100K miles on them running on 5W30 with zero negative outcomes”
However, he also mentioned that there is a 2% return warranty rate on their work. It was not a specific statement as to whether it was transmission or t-case related. So it would be unfair to claim that 5w-30 resulted in certain t-case failures, but it is fair to say that at least some of the time, 5w-30 may have contributed to failures. It is unknown if some t-case fluid levels were neglected, and having 5w-30 in them, resulted in failures attributed to the fluid.
Other Sources of Information:
Other industry competitors to Rockland do not support the use of any fluids other than what is required by the OEM. Specifically, Jasper Engines is also a renowned re-manufacturer. After speaking with their tech support analyst, they recommend use of OEM fluids, and will only warrant their work and products with fluid applications in line with OEM specifications. They had heard of the topic, and discouraged the use of engine oil because it had not been tested nor its performance validated.
Although some may exist, I could not find references to a specific re-manufacturer’s council regarding transfer cases. However, I did find the Production Engine Remanufacturers Association (PERA); they have no comment other than to echo those that are in line with the OEM fluid specifications. Since many re-manufacturers do engines, transmissions, differentials, and t-cases, it’s reasonable to assume the principles apply with consistency.
Transmission Digest, the trade magazine where the article appeared, has no comment other than to refer to the author of the article, Mr. Weinberg. They have no technical staff to validate articles; they simply edit and publish topics from industry contributors.
Other research includes advice from noted active and retired lubricant engineers and tribologists. Several I have spoken with suggest that staying with OEM specs can never be a bad thing, although there is always room for exceptions. However, care should be used before making such alternate selections. ATF and 5w-30 engine oil do not typically share the same viscosity properties; typical ATF has a viscosity of around 7.0 cSt at 100 degC whereas a 5W-30 engine oil is more like 10.5 cSt at 100 degC, so ATF is more like an SAE 15 weight. This would indicate that ATF would flow better into the link plates of the chain. In fact, a 5w-20 would be more like ATF, to mimic the grade of the ATF. NOACK values in a 5w-30 are around 13-15, where NOACK in ATF it is about 18-20. The difference is substantial enough to be considered non-empathetic; it is not reasonably interchangeable.
Details of lubricant characteristics:
The original comment from Weinberg suggests that the 5w-30 was selected for a higher resistance to evaporation. This is probably a good thing to have. But there are many good solutions to finding a fluid that resists evaporation more so than a traditional ATF. “Synthetic” fluids are available in many forms, groups and types. There are good synthetic fluids marketed in ATF formulas that would provide a much higher ability to withstand heat and evaporation, comparable to those of 5w-30 synthetic motor oils. It is probably not necessary to seek out a different type of fluid (motor oil) when an upgraded fluid base stock of ATF can provide the same results, and do it within the confines of the base lubricant properties.
While people would rightly point out that there are differences between additive packages, not all of these are worthy of debate. For example, the detergent and dispersant additives highly present in engine oil mean little to the t-case, because these are to help control soot, insolubles, etc. Since these combustion byproducts are not present in a t-case, the engine oil has no advantage in this regard.
Common sense questions arise from reading the article. First, no information was presented that gave indication of maintenance history for the t-cases involved in helping Weinberg making his determination. We do not know if the t-cases were neglected; perhaps fluid checks and changes were not performed adequately. Second, we don’t know the operating environment that the t-cases were present in, before removal. In a nutshell, nowhere does the OEM or GM indicate these t-cases are “fill and forget” equipment. They must be maintained, including proper fluids and levels. To let a t-case get so low on fluid that damage occurs is not the fault of the lubricant; it’s the fault of the owner for poor/neglected maintenance. If extreme low levels of 5w-30 lubricant were to occur, it’s likely the same disagreeable results would result.
Further, it’s reasonable to think that the OEM and GM considered the operating environment, including temps, angles, fluid levels, wear patterns, gear and bearing loads, etc. After all this, they specified ATF. It is not as though ATF is not capable. Engine oil may work, but it may not work as the designers intended.
Over-filling the t-case is an answer to a question that probably should have been addressed differently. If one maintains the levels properly, there should be no reason to over-fill the t-case. In fact, there are times when over-filling gear cases in general, creates other problems such as aeration, foaming, higher internal pressures, etc. If your fluid level is kept at “normal” design levels with proper maintenance, you should have no need to over-fill. Over-filling the 261,263 t-cases in this scenario has not shown any detrimental effects, but neither has it shown any advantages. There may be proof at the developmental level (OEM) one way or another, but field results don’t seem to reflect cause for concern. Overfilling is likely a precaution that adds cost, but little else.
5w-30 engine oil does have a higher viscosity index property, as compared to traditional ATF. In some circumstances, when used in gearboxes, it has shown marked improvements. However, this is typical of “gear-to-gear” type designs, where direct gear tooth contact is present, similar to a ring-pinion relationship. Here, thicker oil is nearly always preferred due to its viscosity and EP (extreme pressure) additives over an ATF. But even engine oil is overshadowed by true API GL rated gear lubricants in these circumstances. A common “compromise” is manual transmission fluid, which is somewhat a “hybrid” equivalent. However, we must keep in mind that the t-cases in our trucks are not of gear-to-gear design; they are link-plate chain driven. Lubrication between the plates, and to the pins, is just as important as the loading against the tooth/gear contact points.
One the most important things to understand, is that while viscosity gain can be a good thing, it can also be a bad thing. Typically, lubricants are rated at both 40 degC and 100 degC. This is because fluids never operate at just one temperature. Here’s a breakdown of DEX III and 5w-30 typical properties.
DEX III 5w-30
cSt @ 40C/104F 37 62
cSt @ 100C/212F 7.0 10.5
As you can see, while engine oil has a slight viscosity advantage at 100 degC, it is nearly 70% thicker at just above 100 degF. And is gets disproportionately even thicker below that. The problem with engine oil can be that if you don’t get your t-case hot all the time, the engine oil will not flow as well as ATF. ATF does a MUCH better job of flowing at lower temperatures. This is very important when submersion/splash lubrication is being used. So, while it’s true to say that above 200 degF 5w-30 has some advantage, other times, ATF actually flows better. By choosing 5w-30, you are trading high temp performance for low temp performance. T-cases do not always get very hot. There are many times, such as during winter, the t-case struggles to get over 50 degF! That is one time you do not want a fluid to be “thicker”. While 5w-30 works fine in a pressure fed lube system in an engine, it may not be doing that great a job when cool in a partial splash system like a t-case. And while both ATF and engine oil are available in “synthetic” products, it does not greatly change the viscosity properties of the lubricants. Upgrading from ATF to synthetic ATF is akin to moving from 5w-30 to synthetic engine oil, but the basic comparison is valid. So it is still a fair comparison for the above data.
Although not often discussed, it is appropriate to note that the new DEX VI fluid is a significant step above the old “dino” DEX III base fluids, in many regards. DEX VI has roughly twice the oxidation resistance, and twice the viscosity retention over its former fluid. DEX VI is a thinner fluid when starting out, but it stays within grade much better than traditional DEX III fluids, which drop considerably with use. DEX VI will actually be above DEX III in viscosity after some use, because the DEX III drops very steadily; yet the DEX VI holds its grade very well. And although the debate rages in regard to DEX VI usage in Allison transmissions, these upgraded properties may actually perform much better in a t-case. After all, if evaporation is the concern with a traditional DEX III, your DEX VI should last two times as long in the same operating environment. I have found no information in regard to DEX VI being tested by the OEM, but GM does warrant its use in the t-case, and is backwards compatible, per GM, although they do have conflicting documents. However, it is also important to note that DEX VI does not hold any advantage over synthetic (group VI PAO base stock) DEX III fluids. If one were to accept a “good – better – best” analogy, then you could rank the ATF fluids thusly: DEX III, DEX VI, DEX III synthetics, DEX III synthetic TES-295s.
Warranty Issues:
There are different opportunities for warranty coverage, should something happen to the t-case in the case of “normal” use. One is the OEM/Seller warranty. Another is from the lubricant marketer. Lastly, if one has rework done, then there is some expectation of coverage there are well. Let’s look at each individually.
The seller/warrantor (GM) specifies ATF at proper fluid levels. This is considered a routine maintenance item, and is the responsibility of the owner to assure proper fluids and levels are utilized. After speaking with GM, both at the corporate and dealership level, there is no assurance of warranty coverage other that what is in written form in the owner’s manual. Warranty coverage is void if non-specified fluids are used, or in conditions that do not meet with design criteria (over/under filled).
Amsoil has the following to say regarding their products and warranty:
DISCLAIMER & TECHNICAL CONCERNS
Specifications contained on this website are based on manufacturers' information and were believed accurate at the time of publication. Our recommendations apply to AMSOIL products only, as we cannot be responsible for products from other manufacturers. Always compare fluids and lubricants that were installed in the vehicle with those replacing them during service. Never install more fluid or lubricant than what is considered adequate according to gradients on dipstick or level of filler hole. Fill and drain locations are for reference only. Failure to perform adequate inspections or obtain proper resolution will limit or negate any liability toward AMSOIL INC. Models introduced midyear may not have the same specifications as those produced earlier.
Clearly Amsoil has no intent of recommending or warranting anything other than a fluid that is specified by the OEM; this is ATF. Amsoil does have products that they will warrant for use in ATF applications. This is not a comment on whether Amsoil meets OEM specs, but rather what their warranty recognizes as the proper application of their fluids to OEM specs. (I am distinguishing this because some would argue that Amsoil’s products are not tested to meet GM specs, and they’d be right. But I contend that Amsoil will warrant any failure related to lubes that they specify application for. Amsoil would warrant the t-case if you used either the “ATF” or “Torqdrive” products, as they are specified for DEX III and TES-295 applications. However, their engine oils are not specified for those same applications, therefore no warranty would be expressed or implied.)
Mobil has similar constraints:
ExxonMobil Lubricants & Petroleum Specialties Company, a division of Exxon Mobil Corporation ("ExxonMobil") provides this limited warranty to the purchasers who use Mobil brand lubricants in their vehicle.
This limited warranty covers the Mobil 1 lubricant and critical engine parts lubricated by the lubricant.
If there is equipment failure related to the Mobil brand lubricant you purchased, ExxonMobil will repair any equipment damage directly caused by a defect or malfunction of a Mobil lubricant, provided that the lubricant was selected and maintained in accordance with specifications of the original equipment manufacturer or the written instructions (which includes product packaging) of ExxonMobil.
This is specific to the Mobil 1 engine oil warranty, but all the Mobil warranties have the same general wording. Mobil will not warrant a t-case that has their engine oil in it, when the specified fluid is ATF. Mobil obviously has no intent of providing any coverage if improper fluids, or incorrect levels are used. Mobil would indeed warrant the t-case if their D/M or ATF products were used, and they do meet the full spec criteria.
In fact, it’s fair to say that all aftermarket lube companies I could find say similar things; they only warrant their products when used in accordance with OEM specs matching their application guidelines.
Rockland (RSG) says the following in their transfer case warranty: “ … Units will not be covered under warranty if they are run out of lubricant, under filled or overfilled with lubricant, or filled with the incorrect lubricant.” (Note: this is in bold type print not because I upgraded the text, but because RSG denotes it as such, to call attention to its importance). It is an interesting contradiction to the specific recommendation by Weinberg, and one that cannot (as of this writing) be reconciled. However, to be fair, given that the article was written by the RSG company president, there is a certain amount of expectation that the use of engine oil would be covered, but ONLY when used in a t-case that RSG remanufactured, and not one from any other source. RSG would not rebuild your GM backed or Jasper built transfer case, just because you used engine oil. And the corollary holds true; GM or Jasper is not going to rebuild the t-case, should you use engine oil. Each will only warrant their own work, when using the fluids that only they recommend.
Summation:
* The OEM/Warrantor specifies the use of ATF.
* The aftermarket lubricant industry as a whole recommends following OEM fluid specs.
* The remanufacturing industry, with one exception, suggests following OEM specs for fluids.
* The man who wrote the article has provided no credible sources or information to prove that motor oil is “better” than ATF in this application; he does have extensive industry experience
* Lubricant engineers imply the design characteristics should follow OEM design and development
* There is no technical evidence or industry studies available to suggest that using engine oil in lieu of ATF is harmful, nor helpful.
*The anecdotal evidence points to the fact that most failures are due to poor maintenance, and not lubricant selection.
* Engine oil is thicker at all temps; good when very hot, bad when not.
* If a longer lasting fluid is desired, that still performs within the criteria as specified by the OEM/Warrantor, a “synthetic” ATF in either DEX III or TES-295 would be a very good upgrade, without moving outside the operational boundaries of ATF.
Conclusion:
There are many people that successfully run ATF, in its many forms. It is the specified fluid, and has the full approval and warranty support of the manufacturing and lubricant industries. The failures while using ATF are likely attributed to poor maintenance routines. There are upgraded “synthetic” ATF fluids available will provide greater performance characteristics if desired.
There are many people that use basic or synthetic 5W-30 engine oil with great success as well. There are no known failures from using motor oil, although some may exist, but data is inconclusive. This may be due in part to the relative low exposure of people using these fluids, and the relatively small amount time that these alternate fluids have been in service. There is no evidence to show that this is a good or bad choice; the evidence is anecdotal.
Reality check:
There is but one fluid to use in your t-case. And that fluid choice is yours to make. The answer for you, the owner, comes from how you define your preferences, establish your goals, and maintain your vehicle. What other people choose is of no consequence. It was my intent to provide the facts, with credible resources and data. I hope that you find what you need to make your decision. All I wanted to do is set the record straight as to what information is available, where it comes from, and dispel the mythology regarding this topic.
References:
www.amsoil.com
www.gm.com
www.jasperengines.com
www.magna.com
www.merchant-automotive.com
www.mobil.com
www.pera.org
www.rsgear.com (Special thanks to Mike Weinberg)
