Chrysler automatic transmission fluids: 7176, ATF+3, ATF+4
GM Frazier wrote:
For the full story behind the development of ATF+4, please see SAE paper #982674. It is simply packed with interesting data about the development of ATF+4®. Here are a few tidbits:
The initial development was done using Shell's XHVI base oil. Only much later were other Group III base oils approved. (Currently, SK in Korea and PetroCanada are the only additional approved base oil suppliers.) The use of Group III base oils is probably the leading cause for ATF+4 being a more expensive fluid than ATF+3 (which according to the paper uses a Group II base oil).
Lubrizol developed a new shear-stable viscosity index (VI) improver
specifically for ATF+4. The initial tests of this VI improver in the
MS9602 test fluids were so remarkable that Chrysler modified the then-current ATF+2 spec (MS7176D) to include it. Thus ATF+3 (MS7176E) fluid was born; it remained the factory fill until ATF+4. [Lubrizol is still used in ATF+4 and is required in fluids licensed for compatibility.]
In testing done during development of ATF+4, Chrysler noted the following viscosity loss from shearing for the following ATFs (20 hour KRL Shear Test):
Dexron III - 40% loss
Mercon V - 19% loss
Type 7176D - 32% loss
Type 7176E - 14% loss
Type 9602 - 10% loss
You can see what a significant impact the new viscosity improver had on ATF+3 when you compare the 7176D and 7176E numbers. From the standpoint of viscosity loss alone you can see why Dexron III should not be used in transmissions that require ATF+3 or ATF+4. In terms of other basic performance parameters, ATF+3 (7176E) comes the closest to ATF+4, with Ford’s Mercon V a close second. [Which doesn’t mean that Mercon is acceptable.]
The goal in developing ATF+4 was to create a fluid that would match the performance characteristics of the current fluid (Type 7176D), but would retain those characteristics for at least 100,000 miles. The paper specifically notes that the anti-shudder properties of ATF+3 are usually degraded enough by 30,000 miles to cause noticeable shudder.
Contrary to popular myth, one of the stated goals of Type 9602/ATF+4 fluids was that it would have the same frictional characteristics as ATF+3. The paper explicitly states that this was because new clutch materials would not be introduced for this fluid and it had to be backwards compatible with ATF+3. Graphs in the paper show that the friction coefficient of fresh ATF+3 and ATF+4 is essentially identical, but as the fluid ages ATF+4 retains the “as new” coefficient while ATF+3 degrades.
The paper noted that one alternative was to use synthetic Group IV base stock, which are even more expensive than the ATF+4 solution, which provided Group IV style performance from Group III stock. ATF+4 meets strict low-temperature, oxidation, and volatility performance requirements and relatively low cost — believe it or not.
Manufacturers can make ATF+4 fluids, but to use the trademarked ATF+4 name in their compatibility list, they must have their fluids tested and licensed by Chrysler engineers, and must use Lubrizol in their formulations. Licensed fluids are periodically sampled from stores to assure quality.
ATF+3 is a friction-modified, high-quality transmission fluid similar to the current fluid in most respects; but it wears out more quickly and has less desirable cold viscosity (to simplify: is too thick when cold). ATF+3 can be approximated by Dexron plus an additive but this does not save much money and is not as desirable as using the correct fluid to begin with.
Dexron itself is the General Motors-specified fluid from far back in automotive history. While it was once the standard for all American autos, that time has long passed, with Ford settling on Mercon and Chrysler on ATF+3 (and now ATF+4); other manufacturers also require their own fluids.
Engine oil has been used as an automatic transmission fluid, again in the antiquity of automatic transmissions; it is still used in manual transmissions, but generally a single-grade oil is used.
The Center for Quality Assurance, which Chrysler uses to run its ATF+4 licensing program, wrote: “The previous MOPAR ATF+3® formulation was discontinued in 2005 and ATF+4® is recommended for all transmissions filled with ATF+3®.”
Several companies now sell "universal" fluids. If they state that they are compatible with ATF+4®, they may work well, especially for those unsure of which fluid to use. The Center for Quality Assurance warned us to check the label for Chrysler’s license number, and to make sure the fluid is on their list of ATF+4® licensed and tested fluids.
You can use ATF+3 with all older Chrysler transmissions (except some Jeeps as noted below).
Chrysler is not the only company to require a unique transmission fluid. Dexron has long since passed its prime, and modern transmissions require modern fluids, which more refined properties. Toyota, Ford, Nissan, and other major automakers also require unique fluids.
David Castater noted: “I used Lucas transmission additive on the recommendation of my local Kragen counterperson... What a mistake!!!! We started seeing shudder at 55+ mph. The dealership told us it was the torque converter dropping out of lockup and the tranny would fail and should be replaced ($3,000). This was a dealer purchased rebuilt transmission less than 4 years old! My local AAMCO manager changed the oil and filter, added a"friction modifier", and reprogrammed the computer. No problems since!”
Kristen Clark, marketing manager for Lubegard, wrote: “Lubegard has test data on its Lubegard Highly Friction Modified (HFM) ATF Supplement being used in Dexron III in place of Mopar ATF +3. Our packaging includes one of our tests — “Clutch Slip after engagement” — showing the torque curves on it. This compares Lubegard HFM ATF Supplement added to Dexron III vs. Chrysler's Mopar ATF+3. We have proof our products match the frictional characteristics of various other ATF fluids such as Mopar ATF + 4 as well.”