About I-CAR - Current Events/News: e-newsletters: Advantage Online: June 25, 2007

Figure 1 - CVTs offer improved efficiency over stepped 4- and 5-speed automatic transmissions. Chart courtesy of Dr. Z. George Zhang, Valvoline, a Division of Ashland Inc.

Figure 2 - This is the automatic transmission fluid usage timeline for the Chrysler Group. Chart courtesy of Dr. Z. George Zhang, Valvoline, a Division of Ashland Inc.

Figure 3 - This is the automatic transmission fluid usage timeline for Ford. Chart courtesy of Dr. Z. George Zhang, Valvoline, a Division of Ashland Inc.

Figure 4 - This is the automatic transmission fluid usage timeline for General Motors. Chart courtesy of Dr. Z. George Zhang, Valvoline, a Division of Ashland Inc.

Figure 5 - As vehicle speed changes, so does the diameter of the drive sheaves.

Figure 6 - The steel drivebelt is an integral part of the CVT transmission.

Figure 7 - Nissan uses two CVT fluid warning indicators under the hood of their vehicles.

Figure 8 - Vehicle makers that use CVTs also have specific CVT fluid. This fluid is for Honda vehicles.

FLUIDS FOR CONSTANTLY VARIABLE TRANSMISSIONS

In the 1930s, the first stepped automatic transmission was offered by General Motors, followed in the 1980s by Subaru offering one of the first constantly variably transmissions (CVT). Since the 1980s, CVT applications have diminished, only to resurge in the past few years. This is due in part to consumer demand for smoother shifting vehicles, better fuel economy (see Figure 1), and a transmission that is more efficient in using power developed by the engine than traditional automatic stepped transmissions. CVTs require a special transmission fluid, specific to each vehicle maker. According to the Nissan Owner's Manual for a 2005 Nissan Murano, "Using transmission fluid other than Genuine NISSAN CVT Fluid NS-2 will damage the CVT transmission, which is not covered by the NISSAN new vehicle warranty." Other vehicle makers have similar statements.

In 1938, General Motors introduced the first automatic transmission, and then other vehicle makers began introducing their own design. Following the development of the automatic transmission came the requirement of specific transmission fluids for nearly every vehicle maker. Some common types used through the 1960s and 1970s were the Ford Type-F, Mercon, and Dexron just to name some of the more common types.

As automatic transmissions evolved, so did the fluids that were recommended in different vehicle applications within a specific vehicle brand. In some situations, (see the charts in Figures 2, 3, and 4) vehicle makers may have had multiple fluids that were available during a given time frame, but designed only for use in specific transmissions.

In 1989, the Subaru Justy GL became the first production vehicle in the U.S. to offer a CVT. Basically, a CVT uses a steel driveband that rides on two constantly variable cones or sheaves (see Figure 5). Aside from the steel band, a CVT is very similar to a traditional automatic transmission, but without the noticeable shift points (see Figure 6). The smooth unnoticeable shifting occurs by the way a CVT functions. A CVT allows the engine to accelerate up to an optimum rpm, and at that point, the transmission engages. With the transmission engaged and the engine rpm at a predetermined point, one set of the drive cones, or sheaves, open as the other set closes. During acceleration, this changes the speed of the drive belt. Yet, while the engine rpm remains fairly constant, the transmission shifts through its gears and the drive cones constantly change to maintain a steady engine rpm and seemingly unnoticeable shifts.

Some of the vehicle makers that are using CVT transmission technology include Audi, Ford, Honda, Nissan, Saturn, and the Chrysler Group.

CVTs require special care, and as with other types of automatic transmissions, special fluid. Similar to regular ATF, the CVT fluid is a specially formulated product that is not interchangeable with automatic stepped transmission fluid. Using ATF that is designed for use in stepped automatic transmissions will damage the unit, and void the warranty of a CVT unit. Some vehicle makers even seal the unit so it is only serviceable with special equipment, not common in many service repair facilities.

Nissan even prints a caution in the Owner's Manual and displays a warning label in the engine compartment to help keep the unit from becoming damaged by using the incorrect fluid (see Figure 7). When working on a vehicle such as a Saturn VUE or Dodge Caliber, that are available with an optional CVT, always make sure any fluids used or servicing is done following the vehicle maker's recommendations, or the implications could be a tough lesson learned.

Depending on the vehicle makers' chemical formula, CVT fluids will have distinctly different colors. The Honda brand CVT fluid appears to have a thin red appearance (see Figure 8), whereas the CVT fluid used by Ford is green.

As CVTs are becoming more frequently used, it is critical to properly identify the transmission type before servicing or adding/topping off the fluid. With all the options that can be identified in a VIN deciphering section of an estimating guide, transmission type is not one of them. Possibly the only definitive way of identifying if a vehicle has a CVT, is by calling the dealer and verifying through the VIN.

Though not in production yet, in years to come we may see another variation of automatic transmission called the Infinitely Variable Transmission (IVT) which will most likely command yet another blend of ATF.

If the vehicle in your repair facility has a CVT that requires fluid or servicing, be sure to check the vehicle maker's web site information for the specific type of transmission fluid to use. Using a generic ATF, designed for an automatic stepped transmission, can result in extensive damage.

A copy of "Automatic Transmission Fluids, July 12, 2006" by Z. George Zhang, PhD can be downloaded below.

For comments or suggestions on the Advantage Online, please contact I-CAR Senior Instructional Designer Bob Jansen at bob.jansen@i-car.com.

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