The right fluid for the automatic transmission. Parameters, permissions and characteristics

An automatic transmission is a useful thing. The technology of building automatic transmissions and producing lubricants for them has reached such a level that you can not think about changing the oil in the automatic for 4-5 years. That’s if we buy a new car. If we have a car with a mileage, we have to face the problem of choosing a fluid and the method of its replacement. Both problems cause a lot of questions and we will look for answers right now.

What is ATF and why it’s not really oil

The transmission fluids that squirt in our automatic transmissions are called ATF thanks to General Motors. The abbreviation stands for Automatic Transmission Fluids or fluids for automatic transmissions. Americans were the first to use automatic transmissions in serial automobiles, so they were the first to encounter the problem of mismatch between the characteristics of engine and transmission oils.

There were many things that GM was not satisfied with in motor oils. First, hydromechanical transmissions consisted, and even more so now, of heterogeneous parts, metal, synthetic, ceramic, composite. In internal combustion engines, we mainly see metal-on-metal friction. It is very difficult to select such additives that would not destroy the materials of all box parts without exception. This is why motor oils, gear oils and ATF have completely different additive packages.

Second, the fluid must cool the parts, the crankcase, and the hydrobox. If the engine is cooled by antifreeze, the automatic transmission has no separate cooling system. And it heats up quite well, too. Modern GM transmissions can operate at temperatures up to 100-150°C, and the oil temperature inside can reach 900-1200°C. That’s why all automatic transmissions, working with high power engines, have a liquid radiator.

Third, the high pressure and high speed of oil passing through the channels of the gearbox can cause the formation of foam. Foam is dangerous because it in turn causes aeration – saturation of the liquid with oxygen. And oxygen leads to oxidation and rapid aging of ATF and corrosion of aluminum, steel and other elements of the gearbox.

Fourthly, the oil must not lose its viscosity characteristics when it gets very hot – for the torque converter to work, the oil must have a relatively low viscosity, and on the contrary, the viscosity must be as high as possible to lubricate the rubbing parts. And this is probably the most important factor that distinguishes oil from ATF fluids. Therefore, it is not quite correct to call them oils, but habit is sometimes stronger than we are.

ATF classification and specifications. Don’t be confused by the labels

What oil to pour into the automatic transmission depends only on the recommendations of the automatic transmission manufacturer. These recommendations refer only to fluid specifications and tolerances of this or that manufacturing company, but not to ATF brands.

In short, to make it clearer how to choose the right type of automatic transmission fluid, let’s follow the specifications of GM, Ford, and the manufacturer of automatic transmission boxes for trucks, buses, SUVs, the company Allison, a subsidiary of GM for the production of transmissions.

In 1949 GM developed a special oil for automatic machines ATF-A, which quickly spread around the world. In ’57 a new and improved Type A Suffix A (ATF TASA) standard was released. It was also used worldwide for the next ten years.

But suddenly the question arose about the need to revise the standard. The fact was that the fluid contained an animal component, the raw material was whale oil. The consumption of oil was growing and there were no more whales. So GM developed a new standard on the safe side, just in time to avoid a major scandal. In 1969, whaling was banned anyway.

The new standard was called Dextron and this fluid is completely mineral or synthetic based. Ford tied its standards to Dextron and these fluids can be fully interchangeable. Here is a table of interchangeability and development of GM and Ford specifications:

ATF Specification

Mixing and refilling the automatic transmission oil correctly

We did not include obsolete standards in the table for nothing, because they are often used in many European cars in simple manual transmissions. The manufacturer is sure to mention this in the service book.

ATF approvals, what are they

The new automatic transmission oils for the last years of production are almost identical in characteristics. The only difference is in the friction coefficient, or more precisely, friction modifier additives:

• General Motors ATFs are balanced so that as the speed of the transmission shaft decreases, the friction coefficient decreases. The gears shift softer and smoother, eliminating jerks and jolts.
• The Ford specification, on the contrary, implies an increased coefficient of friction under load. The shift jerks are allowed, but the transition from gear to gear will be more accurate and precise.

Fluid standards are clearly approved, meaning that each fluid meets the requirements for viscosity, flash point, foamability and chemical reactions with copper and alloys. But before you choose an automatic transmission oil for your car, we will definitely study the tolerance list of the transmission manufacturer.

And there are not so many of them, but each of them gives recommendations on the use of this or that fluid. Mercedes-Benz, MAN and ZF clearly prescribe what fluid to use in the box of this or that model.

Interchangeability of automatic transmission fluids

A very important question about the interchangeability of oils for automatic machines arose against the background of the wide range of products on the market. No matter how much the big companies try to unify all ATFs, they don’t succeed.

Someone will use a new additive, completely confusing the public with a new fluid brand. The confusion is also caused by the colors: the color of the oil in the automatic transmission is not decisive, because different manufacturers can add dye of any color they want, the color is not standardized.

The budget mineral oil Dexron II D can be safely replaced by the more advanced one, Dexron II E. They have a slight difference in viscosity, nevertheless the basic characteristics are completely the same. ATF with reduced friction coefficient Dexron III is not suitable for automatic machines with smooth shifting.

If you put Dexron III instead of Dexron II, the friction of friction pairs will be insufficient and the gearbox will work with jerks and delays.

When to change the oil in the automatic transmission

Despite the claims of some manufacturers that the oil will last for its entire service life, the oil must be changed. Mercedes Benz was the first to start talking about “eternal ATF” about 20-25 years ago, but in the early 2000s, in small handwriting it was written in the manuals, that it would be nice to change it after 60 000 runs. In practice, even the first symptoms of automatic transmission malfunction should not be allowed in any case.

It is critical to change the oil in the automatic transmission before the disease develops. Otherwise, we run the risk of paying for expensive repairs, and in some cases, we will be forced to buy a contract automatic transmission or a new one altogether. Jerking, delayed shifting, jerking, noise, burning oil smell are the obvious signs that it’s probably too late to change the fluid in the automatic transmission.

In practice, the optimal oil change interval is from 35 to 40 thousand runs. The more often we change the oil, the better for the box. At that, changing of the filter in all cases is highly recommended.

The price of replacement of the oil and filter in automatic transmission is incommensurable with huge sums for repair or purchase of a new unit. Although the schedule may also depend on operating conditions. For example, if our car:

In these cases, you need to change the oil even more often, at least 25-30 thousand km mileage.

Let’s summarize

We found out that you need to change the oil in the automatic transmission, and we found out approximately when. You have to clearly understand that every company has a marketing department. Some benefit from having us change the ATF in the box as often as possible, while others benefit from having us change the gearboxes themselves as often as possible, or better yet, buy new cars.

There are also third companies, which sell magic additives for automatic transmissions, resurrecting the dead and giving eternal life to our automatic transmission. All this is mostly nonsense and to give in to provocations to buy additives for automatic transmissions we do not recommend.

The main thing to remember is to change the oil, not when the box is at death and changing the oil is no more effective than a shaman tambourine, but at least 2-3 thousand km before that. And the more the car is in the risk zone (traffic jams, temperature, loads), the more often we change ATF.