First things first: Oil specifications for engines are relatively straightforward. Most original equipment manufacturers recommend a minimum standard for oil performance based on engine and laboratory tests. For the North American market, that consists of API categories, which are currently API SN Plus and SN Plus-Resource Conserving as well as ILSAC GF-5. GM also has Dexos.

On the heavy-duty side, API CK-4 and FA-4 are the current benchmarks. OEMs have their own labels with some tighter limits on tests or additional tests to differentiate their products.

Europe is a bit more complex, since the latest industry sequences always include several in categories as well as different levels for engines with and without additional emissions systems and heavy-duty applications. Japan also has both industry and OEM specs.

Oil marketers have a relatively simple matrix of product recommendations for sale. Mostly its a good-better-best lineup with two levels of products and several SAE viscosities. Depending on the brand and market served, there may be one or more specialty oils such as those meeting the Dexos specification.

The heavy-duty oil matrix is similar, except high-mileage would be replaced by specialized oils such as gasoline engine oils. All in all, the total number of products is relatively minimal.

Transmission fluids are a whole other kettle of fish. First of all, there are several different types of transmission designs. I wont go into details about the differences, but suffice it to say, there are automatic transmissions, automated manual transmissions, continuously variable transmissions, dual-clutch transmissions and manual transmissions.

Transmissions have a preferred and a not-so-preferred place in various types of vehicles based on the torque requirements of the vehicle. According to Afton Chemical, traditional step-type automatic transmissions are best in heavier vehicles, including light commercial units. Wet double-clutch transmissions are popular in mid-size and racing applications. Continuously variable transmissions are better for lighter applications such as mini and mid-size vehicles. Automated manuals seem to fit across a broader spectrum from very small, lightweight vehicles up to racing and small commercial applications.

Each transmission design has a definite appetite for transmission fluid, and there is no SAE viscosity system to define them. Each type has a preferred viscosity and chemistry unique to itself. In fact, even within a particular family of transmission types, the additive chemistry can be remarkably different depending on the manufacturer.

An example from former years is the difference between Ford and GM fluids. They serviced transmissions of similar design, but Ford always wanted the driver to feel the shift, so very little friction modifier was used. On the other hand, GM wanted a smooth, almost unnoticeable shift, so more friction modifier was used. There were other chemical differences as well.

To give you an idea about the complexity of the transmission fluid market, there are over 100 currently active specifications. These basically differ by transmission design, but there are some instances in which a transmission manufacturer has specified one oil formulation while the OEM that uses those transmissions specifies something else. Talk about confusion!

At this point, you may be asking yourself if there is a possibility that one product could be formulated to meet all requirements. The direct answer is no. As great as that sounds, current transmission fluid specifications have differences in minimum and maximum viscosities that make them mutually exclusive. (See Page 14 of the 2019-2020 LubesnGreases Factbook.) In addition, there are differences in chemistry that also raise performance questions.

In a recent article, Infineum noted that transmission fluids are being called on to provide additional fuel economy performance. Transmission fluid viscosity affects pumping, drag and churning losses. The oil pump is a major source of energy loss in the transmission, so you cant ignore it. Theres also the impact of viscosity and chemistry on gear and bearing efficiency.

A number of OEMs have moved transmission base oil viscosity from around 6.8 centistokes to 5.5 cSt. There are already some 4.5 cSt fluids in use, and there could be a move to lower viscosities in the future.

In a reported experiment, Infineum demonstrated that a reduction in base oil viscosity from 7.3 to 5.4 cSt resulted in fuel economy gains of 1 percent in Federal Test Procedure 75 for fuel economy. Additive changes gained an additional 0.6 percent. Lowering the base oil viscosity to 4.8 cSt and using the improved additive resulted in another gain of about 1 percent.

Infineum went on to note that improved low-temperature viscosity is also critical. Logically, if viscosity is lowered, there is greater risk of wear and friction increasing, so new chemistries are going to be needed to maximize fuel economy gains. On top of that, there will be formulation challenges to improve durability and extend drain intervals. In short, increased fuel economy and more complex transmission hardware will stress ATF, leading to formulation of even higher performing transmission fluids.

All this points to the fact that each transmission design has some unique performance requirements that will make it very difficult, if not impossible, to create a truly universal product. Fast oil change stores and independent maintenance and repair shops continue to have an inventory problem with respect to transmission fluids. Which ones should they stock, and where do they find the ones they dont have on hand when needed? For new car dealers, there is no real problem, since theyll be working on their own brands. Even then, there may be an occasional vehicle that comes in with a transmission fluid need they dont have on hand.

For the independents and fast oil change market, the need for a relatively broad-base product is obvious. The OEMs did something like it before with Ford Mercon and GM Dexron products. These found fairly wide use in the past, but that era has mostly gone away. Now were dealing with foreign name plates such as Audi and Toyota, which brings us back to the beginning of this column.

All four of these vehicle makes are apparently having problems with poor shifting and startups. I dont know the technical details or what cause, if any, has been determined. I could speculate that the wrong transmission fluid was used, resulting in some system malfunction such as deposits due to oxidation; shear loss of the oil, resulting in a partial loss of load carrying ability; or friction modifier failure.

I could also speculate that adding a top treat, which may or may not raise the overall performance of the transmission fluid to OEM standards, didnt work and may have compromised the existing additive system in the transmission fluid. These fluids have very complex additive systems, and getting them just right is sort of like balancing a dime on its edge. It can be done, but its not easy, and its not stable.

So heres what Im proposing: Some organization-probably API-should get the ball rolling on a standard system of transmission fluid identification similar to the engine oil categories. It would be more complex than engine oils and would require transmission builders as well as oil marketers, additive suppliers and ASTM to get to work. It would be difficult; it was difficult getting all engine OEMs, oil marketers and support organizations to reach consensus, but we need it to retain some semblance of sanity.

I guess that the bottom line is this: Be careful which transmission fluid you use.

Industry consultant Steve Swedberg has over 40 years experience in lubricants, most notably with Pennzoil and Chevron Oronite. He is a longtime member of the American Chemical Society, ASTM International and SAE International, where he was chairman of Technical Committee 1 on automotive engine oils. He can be reached at steveswedber@cox.net.