The average of 424,000 miles used with Castrol Syntec (not Syntorq) is somewhat misleading due to the fact that one member threw off the bell curve. That member is “Tdrmbramr” (This is his username on the TDR website) who claims over 700,000 miles recorded with all original components! Castrol SYNTEC is a GL-5/MT-1 rated lube. Of interest, Castrol specifically states in its Data Sheets that Syntec is not for a GL-4 application. Considering this empirical data, it would appear that synthetic gear oil rated to performance criteria GL-5 AND MT-1 is not just an alternative but a pretty darn good alternative to what the OEM originally validated for the NV4500. It would appear the “yellow” metals issue is addressed with the MT-1 rating & the GL-5 rating can take much more severe duty service. There are other TDR success stories with members using synthetic gear oils with the GL-5/MT-1 rating such as Amsoil. But, it would be best to dig as deep as we can since appearances can be deceiving and the NV4500 is not an inexpensive component to be experimenting with!
What does the actual manufacturer, New Venture Gear, have to say about all this? Getting any information from NVG was like pulling teeth. Countless inquires to numerous personnel via email and their telephone tech line resulted in little to no information. Eventually, I got a hold of Charles Armstrong, a NVG engineer willing to say something of interest. Apparently, New Venture Gear doesn’t even specify what to put in its own product! I find it hard to believe that the actual manufacturer of a transmission has no say in this matter. I quote his response to my email inquiry: “In response to your inquiry, New Venture Gear does not set the specifications for the SynTorq LT fluid. We are required to use this fluid by our customers. The fluid is specified by GM and DaimlerChrysler, and must meet their requirements. I would suggest contacting GM and/or DaimlerChrysler for their specification information.” Excuse me…. But didn’t NVG work directly with Castrol to develop this lube? What about all those shift stand tests we keep hearing about? I also pointed out other potential problem areas such as heat. Mr. Armstrong responded: “Concerning the high temperature issue you noted, this is one of the main reasons a synthetic lubricant like the SynTorq LT was required by vehicle manufacturers. In certain applications, transmission fluid temperatures can reach 300F. At such a temperature, mineral-based oils can quickly oxidize, thicken and lose some of their essential properties, reducing their ability to adequately lubricate the transmission. Further, overall useful life of the fluid can be drastically reduced by high temperatures, making the OEM required 'filled-for-life' condition for the transmission questionable at best. Synthetic-based lubricants are less sensitive to elevated temperatures and are not as susceptible to degradation as their mineral-based counterparts.” When I asked for more information regarding the new GL-5/MT-1 rated lubes, I received a very curt reply. “No more response will be forthcoming from NVG.” That was not exactly “happiness” to help me!
So, let’s at least analyze some of the important pieces of information that NVG gave us. 300degF! How can a transmission get so blazing hot? Many TDR members might say their NV4500 never overheated and that they monitor their NV4500’s with a temperature gauge. I posted a question on the TDR website; “Who has a temp gauge in a NV4500?” to get a response. TDR members reported seeing as high as 225degF pulling hard in hot ambient conditions and averaged 190-200degF pulling hard in normal temperate conditions. NVG says temperatures can reach 300degF. Why the discrepancy? Kevin Dinwiddie is a TDR member who works for LE (Lubrication Engineers) and is a Certified Lubrication Specialist by the STLE (Society of Tribologists and Lubrication Engineers). Kevin has worked in the oil business for over 22 years and responded; “An overheated condition does not always show up on the temp gauge. It happens between the gear faces with lugging or heavy loads and happens over time. I have not seen any high temps that are over 230 degF in any transmissions all the time. 230 degF is where the sulfur additive starts to have problems. Since you will not see the actual temps between the gear faces on your temp gauge then you will not know that you are having any problems.” So even with a temperature gauge, we can’t see the whole picture. We certainly can’t see what NVG can see with the test equipment specifically designed for that purpose. They did test it didn’t they? I think we all thought that the filled for life concept from DaimlerChrysler was “questionable at best”! It stems from the liability problem of demanding a specific lubricant and not supplying that lubricant to the customer for free. Making it factory “filled for life’ came out of the legal department, not the engineering department, and obviously is not in the customer’s best interest. The Magnuson-Moss Act is not the scope of this discussion, so we won’t go there.
OK, what about the repair companies that rebuild transmissions? Standard Transmission of Texas is a transmission rebuilder of countless NV4500’s. They tried some different lubes in the very beginning to try to offset some of these lubrication costs. Mike P. of Standard Transmission responds: ”When we first began rebuilding the NV4500s, we couldn't find a good reason to use the expensive oil. We advocated using 30w oils of various kinds to keep the cost within reason. We soon found out that the Dodge units HAD to have the Castrol, but the Chevys were okay with just about anything. The Dodge units burned the gears up. The reason we came up with is that the GM units just don't have enough engine to make them work as hard as a Dodge, so they wouldn't burn up. The Dodge is usually used much harder than the GM, so it builds up more heat. So actually, we never did any exhaustive testing, just trial & error that led us back to the Castrol..” I can understand why Standard Transmission experimented with 30wt oils. A lot of transmissions required just that. For example, between 1988 and 1991 either Synchromesh OR 5w30 engine oil was perfectly acceptable in the NV3500. The reason many manufacturers use motor oils is that petroleum gear oils frequently do not shift well at low temperatures. Motor oils and ATF’s are more fluid at these reduced temperatures and are not harmful towards the synchronizers. Unfortunately, these oils provide little to no extreme pressure protection. The shearing action of a manual transmission is much greater than the shearing action in an engine or automatic transmission. Also, a 75w85 gear lube works out to be closer to a 10w40 motor oil than a 30wt oil. When the relatively large amounts of torque produced by the mighty Cummins powerplant was applied to the NV4500, it simply did not have enough protection with engine oil it and it simply over heated.
Technically speaking, MT-1 is NOT a designated replacement for GL-4. GL-4, which contains some obsolete test procedures, WILL BE DELETED in the future and replaced with a new category. Industry insiders refer to this as the “GL-4 Upgrade”. This new category would also address the needs of light duty axles & commercial Synchromesh transmissions. The CURRENT RATING GL-4 IS IN FACT OBSOLETE!
I pointed out these deficiencies in the GL-4 rating to Ed Brown. His reply; “This gentleman makes a very good argument and he seems very knowledgeable on this topic. The API (American Petroleum Institute) recognizes that there are deficiencies with GL-4 quality lubricants, and has created a new category for ASTM to work on which will replace API GL-4. We often refer to this as the new manual transmission category or the "GL-4 upgrade." Because most of the tests specified under GL-4 are no longer available.” The GL-4 rating may be obsolete, but the GL-4 APPLICATION CERTAINLY IS NOT. Oil technology has advanced dramatically. We will have to wait for the new GL-4 “upgrade” to be implemented if you want to know absolutely, positively what you can put in the NV4500 as a safe alternative. Brown continues; “The quality of gear lubricants has improved tremendously over a relatively short time period. This is mainly due to improved additive technology. It is very likely that an old GL-4 lubricant (based on a non-thermally stable additive), at twice the additive treat level, would not meet both GL-5 and MT-1 performance requirements. However, a GL-5/MT-1 quality lube at half the additive treat level would meet GL-4 performance and benefit from improved thermal stability and copper compatibility.”
Empirical data suggests that certain synthetic GL-5/MT-1 rated gear oils will do the job, especially with their good copper compatibility. In one of my queries to Mr. Brown I pointed out the “cleanliness” of the new MT-1 category and talked about the corrosive nature of EP additives and their reaction with heat etc. I pointed to some empirical data suggesting a gear lube with a GL-5/MT-1 rating looks like a better choice than an ordinary GL-4. Apparently even Shell Oil has heard anecdotal claims that GL-5/MT-1 gear oils have performed well, but no OEM is confident that they will provide satisfactory field performance. Certain OEM’s have dropped their recommendation of long drain intervals to relatively short ones. GL-5/MT-1 gear oils work but no one feels comfortable with how long they will work. Brown explains; “Despite the fact that GL-5/MT-1 lubricants meet an ASTM D 130 requirement of 2A max. (after 3 h @ 121.1C) and GL-4 lubricants have a D 130 requirement of 3B max. (after 1 h @ 121.1C), we do not recommend GL-5/MT-1lubricants for GL-4 applications. GL-4 lubricants are frequently used in synchronized manual transmissions. These transmissions frequently have yellow-metal-based components such as synchronizers and thrust washers. We have heard anecdotal claims that GL-5/MT-1 gear oils perform well in these applications. Depending upon the drain interval, the duty cycle and the additive treat this may be true in certain situations. However, I would be concerned with pitting of the yellow metal when using a GL-5/MT-1 lubricant, especially with an extended drain interval or severe duty cycle. Note however that OEM's are not confident that a GL-5/MT-1 lubricant possessing satisfactory D 130 performance would provide satisfactory field performance. Therefore, Meritor does not allow use of GL-5/MT-1 lubes in their transmissions, and Eaton allows them in transmissions only with a fairly low drain interval (60,000 miles; on-highway service). Given the problems with transmission oil cooler corrosion (the coolers are copper), Eaton dropped its specification allowing for 250,000-mile drain intervals for approved GL-5/MT-1 gear oils, and recommends a maximum 60,000-mile on-highway service oil drain interval if MT-1 oils are used in their transmissions.“ Oh Mr. Brown, I love that detail! Now, that was “happiness” to help me!
Also remember that we don’t know how much EP additive is a GL-5/MT-1 rated lube. I did not find any test currently performed on gear lubes to detect the presence of EP additives. Which gear lube has EP additives and how much? We don’t know unless the manufacturer tells us. Dinwiddie comments: “I believe you are right in stating that there should be a test for buffer package amount or type and it's effectiveness over the long term. I do not know of any test like that but it may exist somewhere.”
We also don’t know what buffers are added, if any, to offset the corrosive EP additive. And if they are buffered, we don’t know how long these buffers may work. Dinwiddie adds; “I believe that you’re fighting an uphill battle, why? Because there is no way to determine if a company has used a buffer package or if the buffer package that they used will last for the oil change that the owner wants to go.” Kevin continues; “Yes the LE Gl-5 oils will reduce wear that a GL-4 will not, however, if it was my own truck, even I would use a GL-4---Why? Because you never know what you are going to have to pull or who might drive your truck and lug it or spring a leak and over heat it”
To confuse matters further, we don’t even know how much EP additives is in a GL-4 lube either. Brown states; “we often use the rule of thumb that an API GL-4 treat rate is half that recommended to meet the requirements for API GL-5. That is because API GL-4 applications do not require the high levels of EP performance (manual transmissions use spur of spiral bevel gears) and these high sulfur levels can be detrimental to copper compatibility. However, this rule of thumb is not the optimum situation, and this fact has finally been recognized within the industry.” Rule of thumb? That is not exactly a precise measurement, is it? Is any GL-4 safe or just the one the OEM recommends?
Is this risk really worth the reward? Brown continues; “Since applications calling for a GL-4 oil don't need the EP performance of a GL-5/MT-1 oil, the very real possibility for yellow-metal corrosion is not worth the risk. We suggest that customers follow the OEM lubricant recommendations for their equipment. If an OEM recommends a GL-4 lubricant, we would not recommend using a GL-5/MT-1 lubricant for the application.”
In spite of NVG’s lack of cooperation, we do know Syntorq LT is a very good gear lube, compliments of Castrol USA. Lubricants are often designed to provide a viscosity that is low enough for good flow characteristics in cold weather and high enough to provide adequate film thickness and lubricity in hot, high-severity service. When this hot and cold performance is required, a small response to changes in temperature is desired. The oil industry expresses this response as the V.I. (Viscosity Index). From the Data Sheets of Syntorq we find that it has a relatively high V.I. of 166. A high V.I. also indicates it is a better quality base stock to begin with. Lubes that have a high V.I. also have a lower sulfur content. Sulfur is also part of the corrosive equation that we need to avoid. Multigrade oils were first additized with polymers to increase the V.I. of an oil. Additives do not last the lifetime of the base oil, so the benefit of having a high V.I. without the additives are obvious. I also found out Syntorq is uniquely polymer free.
Specification SAE J306 was revised in June 1998 and became mandatory in January 2000. This is the first time that an SAE gear oil specification has had a shear stability requirement. It must meet the 100degC kinematic viscosity stay-in-grade requirement after a 20-hour KRL Shear Stability Test. It is quite possible many gear oils may fail to satisfy the new shear requirements due to a variety of reasons; for example, being formulated too close to the low end of the 100degC viscosity limit, or using a pour point depressant or viscosity modifier with insufficient shear stability. You guessed it, Castrol claims Syntorq meets SAE J306 too! And before 1998, Castrol used the Kurt Orbahn Shear Stability test on Syntorq to qualify its performance.
Trust me when I say my entire goal was to research a viable alternative to the OEM recommended lube. I had trouble finding any gear lubes even in the same viscosity grade. I only found one lube that even comes close in rheological terms and it wasn’t a GL-5 but a synthetic GL-4 specifically made for synchronized transmissions. Remember that the NV4500 is splash lubricated. There is no oil pump or filter in this unit, so the viscosity of the lube is extremely important and not all 75w90’s are created equal in that respect.
As far as base stocks, EP additives, buffer compounds and who uses what; knowledge is pure profit in the science of the lubrication industry and no one is sharing. There might be an equivalent gear lube at a more reasonable cost, but without a degree in petroleum engineering and the resources to test it, I won’t find it before the new GL-4 “upgrade” category comes out.
Syntorq is specifically tailored for the NV4500, no 75w90 GL-5/MT-1 I looked at even approaches it in rheological terms. It meets the new SAE J306 shear stability test. It has a higher V.I. than any of the GL-5/MT-1 alternatives I looked at and is polymer free. The NV4500 doesn’t need the extra protection of a GL-5, so why take the risk? It’s my opinion that Syntorq is the “Holy Grail” of gear lubes for our beloved under engineered NV4500. Unfortunately, Syntorq LT also comes with the “Holy Grail’s” price too! Well, what should you do? Use a less expensive GL-5/MT-1 lube (change it frequently to mitigate the risk), use the expensive Syntorq and be sure, or wait for the new GL-4 “upgrade” category to see what life brings us? Me? My only temptation would be to try a qualified synthetic GL-4 specifically made for synchronized transmissions, but I’m more inclined to just bite the bullet, pay for the Syntorq and not worry about a thing…
Your best dealer choice for Syntorq is General Motors. Ask any GM dealer for P/N 12346190. It will be substantially less than any Dodge dealer will. You can also obtain a wholesale price for Syntorq plus shipping charges from Standard Transmission of Texas.
Remember, “Tdrmbramr” and others that are experiencing good results with gear lubes rated GL-5/MT-1 have rolled the dice and won. My hats off to this pioneering spirit but can you be the same type of pioneer? For example, their frequent lube changes may have mitigated the corrosive chemical reaction that takes place over time under heat and pressure. “Tdrmbramr” changed his lube every 6 months or 100,000 miles, whichever came first. He also took the transmission apart and measured it! Will you? And what really was the duty cycle in these cases? How hot did they actually run? Were these lubes really put to the test? They are too many variables to objectively give these lubes the unconditional thumbs up. Rockland Standard Gear in New York is another transmission rebuild shop not happy with Syntorq cost. They also are using a GL-5/MT-1 gear lube marketed as their own private label “Rockland Standard Synthetic Gear Lubricant” with good success in urban fleet vehicles. But Rockland’s GL-5 has a 1B rating which far exceeds the MT-1 standard for copper compatibility. This also indicates that it’s very likely a mild EP version and would have a much greater chance of success than a typical GL-5/MT-1. I don’t have any more data on that lube to objectively comment further. These new generation synthetic GL-5/MT-1 gear lubes appear to work OR maybe it’s like the eating. It takes putting the wrong fluids and food in a body over time. It’s not like you eat one bad thing and BAM your sick with congested arteries etc! No, that takes time and that time varies depending on how that body is used. Then the end comes and you realize what you have done. But it’s too late…
If you currently use a GL-5/MT-1 rated gear lube, change it religiously and on a fairly short interval basis. You will be probably be OK in most situations. Is probably OK an acceptable risk factor? That’s up to you. If there is harsh shifting present under cold conditions until it warms up, your lube probably doesn’t have the correct viscosity characteristics and not flowing properly. What else might it not be doing correctly?
Southwest Research Institute, Inc. (SwRi) , Lubrizol Reference Library, Society of Tribologists and Lubrication Engineers(STLE), Don Johnson (NOT from Miami Vice but VP of Product Engineering @ Pennzoil Products Co SAE & STLE member), American Society for Testing & Materials, American Petroleum Institute, Ed Brown of Shell Oil Company, Kevin Dinwiddie of LE & STLE, Kenneth Koliba & Charles Armstrong @ New Venture Gear, TDR members participating in NV4500 OIL SURVEY,
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