Automatic-Transmission Fluid: What is today’s reality? - Transmission Digest

Automatic-Transmission Fluid: What is today’s reality?

Long gone are the simpler times of having just one or two types of transmission fluid. Throughout the 1950s, ’60s and early ’70s, there were basically GM type A or type A “suffix A” and Ford type F. Because of a changing environment, such as increasing engine/transmission temps as well as a fluid-component issue (remember the ban on sperm-whale oil), fluid started to evolve.

Technically Speaking

  • Author: Mike Riley, Technical Editor
  • Subject Matter: Automatic transmission
  • Issue: Correct fluid usage

Long gone are the simpler times of having just one or two types of transmission fluid. Throughout the 1950s, ’60s and early ’70s, there were basically GM type A or type A “suffix A” and Ford type F. Because of a changing environment, such as increasing engine/transmission temps as well as a fluid-component issue (remember the ban on sperm-whale oil), fluid started to evolve.

With the whale-oil component no longer available, GM released DEXRON™ II (C and D) to service its vehicles. At Ford, a significant change in friction material in the early ’70s required that a new fluid be developed, which resulted in Ford type CJ. Unlike type F, the CJ fluid was comparable to DEXRON. A slight deviation occurred at Ford with the launch of the C5 with a centrifugally locked converter. Type H was released to accommodate C5 models. By the mid ’80s, MERCON® was developed to replace type H.

Automatic-transmission fluid is one of the most-difficult oils/fluids to formulate, due to the variety of additives that are required. Engine oils have their set of components; however, ATF has that and more.

ATF can be broken down into three categories: base oil, additive package and, more recently, increased focus on viscosity modifiers. Because of increasing fuel-economy demands and more-sophisticated electrical components, fluid viscosity is more important than ever. Solenoid function is greatly dependent upon fluid viscosity.

The following is a list of additives and their functions:

The starting point is, of course, the base oil, which is broken down into different groups. From there, the appropriate additive packages are added along with the correct viscosity modifiers to meet OEM requirements. Variables also exist between factory fill and service fluids.

During development, determinations must be made as to how one additive component will impact the others. Although all additive components are important, two stand out that can contribute to optimal transmission operation.

Friction modifiers

Engine oils use friction modifiers as a means to reduce wear, as does ATF in automatic transmissions; however, in a transmission there are other concerns. Friction clutches, bands and torque-converter lockup pistons all rely on friction modifiers to provide the best apply feel and durability over a wide range of variables and for a significant amount of time.

Newer transmissions especially can have more than one type of friction material within the unit that must be addressed with one fluid. If an incorrect fluid is used in a given transmission the outcome could be disastrous. Initially, the transmission may shift or lock up OK but as time goes on could start to apply worse, to the point of failure. The failure could then be blamed on something else, incorrectly. With the array of transmissions on the road today, picking the right fluid beyond the recommended OE spec is a real chore. Clutch-to-clutch shifting presents even more complexities due to the apply/release timing of each component.

Viscosity modifiers

Viscosity-index (VI) improver has always been important to engine oils and transmission fluids, but not as much as today. Gear-train parasitic loss can be magnified by an incorrect fluid; however, there is a bigger concern. Solenoids, switches and sensors today are much more complex and sensitive to fluid type. A valve-type solenoid like a variable force motor or linear solenoid with pulse-width-modulation (PWM) operation can be affected by fluid viscosity over a range of temperatures. If a solenoid doesn’t fire correctly, bad things happen, initially or long term.

Companies like Lubrizol and Infineum devote a great deal of time to developing a specific additive package for the OEMs, on the basis of several requirements.

Gear range, torque capacity, computer strategy, transmission calibration, friction material/steel microfinish and ATF all combine to provide a good-working, long-lasting transmission. Changing any aspect can cause problems.

DEXRON III had been the workhorse of the industry for years until DEXRON VI was released in the mid-2000s to accommodate the newer transmissions, such as the six-speeds. On the Ford side, MERCON gave way to MERCON V, which many people equated (incorrectly) to DEXRON III; however, more changes began in 2003 with the 5R110W.

A couple of new fluids have been released recently, such as MERCON SP (5R110W) and MERCON LV (Figure 1).

Even low-volume transmissions have gotten a specific fluid, such as the FNR5 produced by Jatco. Not only does Ford have an FNR5 fluid, but so does Mazda (Figure 2). Are the Ford FNR5 and Mazda M5 the same?

Chrysler also went through the fluid phase, upgrading from DEXRON to the type 7176 and type 9602, becoming ATF +3 and ATF +4. Beyond developing the 62TE and using Mercedes transmissions like the 722.6, Chrysler has also added eight-speeds to the mix.

The import side of the equation is even worse. It seemed as though each manufacturer had to have a different elixir, whether needed or not. One of the most-infamous import brands of fluid is, of course, Honda (Figure 3). For years, rebuilders have had fits with different shift issues with Hondas because of the unique blend of friction material, steel microfinish, calibration and fluid. A deviation of one item and big problems arise.

Hyundai and Kia used Japanese transmissions for years but finally came into their own by producing in-house transmissions and developing their own fluids. Mopar® fluid got the job done on earlier models, but as newer models were launched, fluid requirements changed. The Hyundai/Kia SP III was recommended for later-model four- and five-speeds, but that was changed with the release of the six-speeds and SP IV fluid (Figure 4).

For a time, Mercedes and ZF transmissions would function well on GM fluid; however, as the five- and six-speed models were released, a greater emphasis on the correct fluid was needed. With the launch of seven-speeds at Mercedes and now eight-speeds from ZF, using the correct fluid is mandatory.

Although the majority of transmissions used at Nissan and Subaru have come from Jatco over the years, other units were provided by companies such as AISIN, and guess what: Different fluids are required (Figure 5). Aside from different manufacturers are different models, like older four-speeds to newer five- and seven-speeds, all with different requirements.

As with other import manufacturers, Toyota did exist on DEXRON quite well. As time went on, internal changes occurred such as friction materials and shift strategies, requiring alternate fluids. Initially, the T-IV version was used, but with more changes and models came other flavors like WS (Figure 6). Extreme use of the vehicle can also be a contributing factor.

Beyond regular step-type transmissions are the variables, such as a continuously variable transmission (CVT), which absolutely require a different liquid. The internal pressures and stresses of a CVT demand a fluid with superior attributes, and even within the CVT model offerings are different requirements. The use of an incorrect fluid in a CVT can be even more disastrous than with a planetary-gear transmission, since the belt can weld to the pulleys without the right friction modifier. Jatco provides CVTs to Nissan and Chrysler, but yet both car companies have their own brand of fluid (Figure 7).

One more variation from the norm is the dual-clutch transmission (DCT). A DCT is basically a standard transmission that has been automated (pump, valve body, clutch-pack assembly etc.) with a unique apply characteristic. There is no torque converter or standard-type clutch for initial takeoff; therefore, it’s the dual-clutch assembly doing all the work. Volkswagen was the first to use a DCT, which certainly takes a different fluid from the norm (Figure 8). The A2 fluid, which is used in many of the VW models, is the company’s own special blend; go figure.

For years, oil companies such as AMSOIL, Mobil, PEAK, Pennzoil, Valvoline etc. have produced various synthetic blends that supposedly apply to a variety of vehicles. The question is, which brands cover the most vehicle applications and at what cost?

Fluid-additive manufacturers, like Lubrizol and Infineum, work closely with the OEMs to understand and tailor an additive package for a given application. To deviate from that can lead to problems or failures.

There are organizations that can test and validate the compatibility of specific oils and fluids. The Petroleum Institute of America (PIA) does extensive work to qualify oil and fluids and can determine which ones do not measure up.

In speaking with several shops and rebuilding facilities, it becomes apparent that there is no clear-cut approach to fluid choices. Beauty is in the eye of the beholder. In the end, what works is what counts, so it’s best to buy from someone who stands behind their fluid performance.

The purpose of this article is to not only provide information but also to query the industry as to best practices and determine the “reality of today.” We welcome responses from the industry on this matter in hopes of narrowing the field of options. Reply to [email protected].

Special thanks to Dale Warmuth of Leon’s Car Care Center in Eureka, Calif., for his recommendation that we do this article.

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