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The key question regarding transmission fluids

Do you need OEM-specific fluids? It might not be a simple yes or no.
Tuesday, March 31, 2015 - 07:00
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When you answer technical questions about automotive lubricants, some of the most recurrent questions are about automatic transmission fluids (ATF) and their applications. Perhaps the most often asked question is, “Do I really need OEM specific fluids?” Like most technical questions, the answer never is as simple as a straight yes or no. Perhaps a little ATF history will help clarify the issue and at least explain how we got to where we are today.

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Prior to 1990, there were basically two ATFs - DEXRON/MERCON ATF and Ford Type F ATF - that were in every shop and were used to service everything. A few OEMs (Chrysler and Toyota) had their own fluids, but in general, service choices were simple and new vehicle warranties were short.

The changes really started with the advent of electronically controlled transmissions. Engineers quickly found one of the most important factors for maintaining shift quality was having an ATF that did not change viscosity during the life of the fluid. This was possible, but would require improved additive packages, better viscosity index (VI) improvers and high quality base oils. The fluid specifications at that time were changed to require performance that could be obtained only by using these new improved additives and synthetic base oils.

These programs were very successful and they got what they were looking for: shear stable ATF with outstanding oxidative stability that would meet the new extended warranty being offered by some OEMs. The only problem was these new fluids did not shear down to a viscosity that met the requirements of the new 6-speed transmissions (the same thing is true for newer 7-, 8-, and 9-speed automatics) that had reduced sump volumes, higher fluid turnover rates (aerodynamic shrouding inhibits air flow over hot transmissions) and increased temperatures from heat generating electronics in the transmission itself. When you factor in reducing viscous drag in the transmission drivetrain, it became very obvious to many OEM engineers that reduced viscosity ATFs would be a winner.

New transmissions were designed for them, and each transmission manufacturer had its own requirements for frictional properties and a desire for a new profit center developed around exclusive use of its OEM-branded fluid available through the dealer network. OEM service departments were programed to deny warranty if “improper” fluid (anything not sold by them) was used for non-dealership service. By 2015, the list of OEM-specified and required ATF has more than 100 types available. When you include all types of automatic transmission fluid like CVT fluid and DCT fluid, the list gets even bigger and more complicated. because of the unique properties CVT and DCT fluids have.


The Original Question Again

With that said, back to the question, “Do I need OE specific fluid?” Because the U.S. automotive aftermarket is the dynamic free market entity that it is, there always will be an oil company that is willing to take the same technology it sells to OEMs and package it for consumers available at their favorite source for non-OEM lubricants. Recognizing the need for shear stable synthetic ATF, many manufacturers have products designed to meet the OEM requirements for automatic transmission fluid.

Because the different OEMs have different engineering requirements some of the new synthetic transmission fluids are conventional viscosity (6.8-7.5 cSt at 100 degrees Celsius) while other synthetic automatic transmission fluids are reduced viscosity (5.5-6.5 cSt at 100 degrees Celsius) “fuel-efficient” type formulations.

When determining what to use, following OEM reasoning helps in the decision making process. Some OEMs view reduced viscosity ATF as reverse compatible to older transmissions (GM (DEXRON VI) and Honda (Honda Genuine DW-1) specify their new reduced viscosity ATF as reverse compatible), while others like Ford, Chrysler and Toyota do not and have multiple, specified OEM fluids to meet specific requirements. Aftermarket fluids always will have a product information sheet (often on their website) that gives you viscosity information, so picking an equivalent is not difficult. Because frictional properties are what drove much of the proliferation of OEM specific fluids, this must be factored in when selecting replacement fluids.

Many oil companies will specify the frictional applications of their aftermarket synthetic ATF and have different versions for different vehicle applications. These normally are listed on the product sheet or online. There also are well-respected aftermarket transmission fluid supplements that provide the desired frictional properties. They also have literature and informational websites that guide the user to the correct products and the correct type of ATF to use when using non-OEM fluid solutions.


Up Next, CVTs

The next group of automatic transmissions to consider is the CVT transmission that is becoming very common. Just like conventional automatic transmission, they require frequent service and fluid changes to provide the longevity modern motorists have come to expect. A common mistake made is that CVT fluid and conventional ATF are similar. CVT fluids provide many of the same functions of ATF like hydraulic system operation, cooling and wear prevention.

Where they differ is frictional properties. ATFs are designed to slip clutches properly with no shudder or chatter, where CVT fluids are designed to have a very specific coefficient of friction that allows them to protect the sheaves and belts/chains from wear without excessive slip, making them what we call traction fluids. Using OEM fluids makes sense to many during the warranty period (CVT transmission can be very expensive), but there are excellent synthetic CVT fluids now available in the aftermarket that meet the quality and frictional requirements of the OEM specified fluids.

The final type of “automatic gearbox” we are starting to run into is the DCT transmission (dual clutch transmission). There basically are two types: wet clutch and dry clutch. Dry clutch is used on smaller cars with lower power output engines. The wet clutch DCT is often a high performance option and is gaining popularity because it has an automatic mode that allows the gearbox to shift itself. Dual clutch fluids are the same type of fluid for dry or wet applications. The mechanical/electronic systems (mechatronics) that cause the gear shifts on the dual shaft setup require a fluid similar to ATF.

Because there is a dual mass flywheel that conveys power to the selected shaft/gear wet clutch, the fluid has frictional properties like an ATF to slip the wet clutch properly for smoother shifting. Unfortunately, this is where the similarity ends. The DCT fluid has to contain a much higher level of extreme pressure (EP) anti-wear additive than ATF to ensure gear drivetrain longevity. This requires a fluid formulated to meet the anti-wear requirements of these types of fluids. Once again, the automotive aftermarket in North America has DCT-specific synthetic fluids currently available to take the place of expensive or hard to get OEM transmission fluids.

The answer to the question, “Do I really need OE specific fluids?” obviously is no, but you need to make sure the fluids you chose are designed to perform the way the OEM fluids do. Technology and high quality products are not exclusive to OEM dealerships, but you have to know what is required and make sure what you use meets those needs. There are several aftermarket companies that make specifying OEM alternatives their daily business. It would serve the informed consumer well to remember this and seek the advice and products of these experts.


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