Know which automatic transmission oil to use
by Jim Kerr

It used to be so simple. There was Type A or Type F. If your automatic transmission needed oil, you only had two to choose from. Many Fords used Type F transmission oil while Type A was used in everything else. Today, there are several types of oil specified for automatic transmissions. Using the wrong one can cause shifting problems or even damage your transmission. Here are the more common automotive transmission oils used today.

Dexron Automatic Transmission Fluid (ATF) is probably the most common oil found on the parts shelves today. It used to be called Type A transmission oil but as improvements were made to the oil, the name was changed to Dexron. Many types of Dexron oil have been used over the years. The original Dexron oil became Dexron II, which developed into Dexron IIE in the early 1990's. Dexron IIE used extra additives that helped clean computer-controlled shift solenoids and pressure control solenoids inside the transmission. After only a short time, Dexron IIE became Dexron III, which is still the current Dexron designation.

So which one should you use? The answer is easy. Dexron III is the only Dexron oil available and it can be used wherever Dexron oils were specified. Most General Motors vehicles, many foreign manufacturers, Chrysler vehicles (up until about 1997} and even Fords from the 1950's listed Dexron oil as suitable for their automatic transmissions. Dexron has even been specified in some industrial hydraulic systems and power steering systems, although most automobiles use special power steering fluid for their power steering.

Type F oil has traditionally been associated with Ford vehicles prior to 1977, but is was also used in some other makes between 1977 and 1981. Type F oil has different additives in it that match the friction characteristics of the clutch plates used in their automatic transmissions. The additive package in Type F oil is very strong, so one litre of Type F oil added to several litres of Dexron oil will essentially change all the oil to have Type F characteristics. For example, if Type F oil was added to a GM vehicle, the shifts would feel more aggressive. Type F oil is not interchangeable with MERCON ATF.

MERCON ATF is used in most late model Fords up until 1997, when MERCON V ATF came into use. MERCON ATF is much like Dexron and many ATF labels will list the oil as suitable for both Dexron and MERCON applications. MERCON V is different. Beginning in 1997, Ford began building transmissions for some of their large cars, trucks and vans that require a MERCON V ATF. Generally, MERCON V and MERCON oils are not interchangeable although there are some ATF brands on the market that meet the specifications for both. Check the label on the ATF container carefully!

Although Chrysler has always had their own ATF specifications, they also listed Dexron as an acceptable replacement. That changed in 1997 with the introduction of their ATF+3 fluid. ATF+3 is suitable in any vehicle calling for ATF PLUS, ATF+2 or a Type 7176 ATF. Some Mitsubishi and Hyundai transmissions also use this oil.

Some vehicles have very specific oils for their automatic transmissions. Honda for example, uses engine oil for automatic transmissions in some models. ZF automatic transmissions found in many European and some Asian vehicles often specify ESSO LT 71141 or T-IV ATF only! There are also synthetic transmission fluids available on the market, but before using one, make sure it meets the specifications for your transmission. One-way roller and sprag clutches used in many automatic transmissions require some friction to work, so the wrong oil can reduce their efficiency and cause them to slip.

The owner's manual will list the proper type of fluid for your vehicle's transmission, or if you can't find it, check at your local dealership for their recommendations. While most quick lube places have listings for most vehicles, they may not be familiar with your particular vehicle and could add the incorrect oil. Know the type of oil your transmission needs and be sure to ask what they are adding before they put any in.

The automatic transmission has come a long way from a novelty introduced in 1940 by Oldsmobile to the highly sophisticated computer-controlled gearbox of today. So have the oils. Use the correct oil for your transmission to prevent damage to this essential part of your vehicle's driveline.