Transmission fluids seem fairly simple — manual transmissions ought to take gear lube, and automatics ATF. But neither is as simple as it looks.
Most import stick shift transmissions take 90w, now usually available as 80W90. One early exception is that most MGs, as well as other English cars and Volvos with the Laycock DeNormanville overdrives, use engine oil. 30W was the original specification, but 20W50 is OK in a pinch.
Some of the newer Japanese transaxles require ATF, even in the manuals. And ATF isn’t quite as simple as it looks, either.
Originally, General Motors transmissions used a fluid known as Dexron, and everything else used the Ford specification fluid. A common application for Ford ATF is the Borg-Warner transmissions used in many European and Japanese cars up into the 1980s.
There is a slight difference in viscosity; a oil company rep once told me that transmissions will operate on the wrong fluids, but that a GM transmission will shift rough with Ford fluid, and a Ford trans will be mushy on Dexron.
Dexron has been reformulated twice, so what we get now is Dexron III, which contains additives which offer greater resistance to temperature degradation. I was told that the current formula contains rapeseed (also known as canola) oil, which is supposed to be as good at preventing the fluid from turning into a black gooey mess as the original whale-oil derivatives that were used in the original Dexron. There are also additives available (the major one is Lubegard) which also offer protection against heat damage to the transmission fluids.
Some years back, we started to see cars calling for a new Ford fluid, originally called FA6, now Mercon. It turned out to be Dexron, and so you often see Dexron labelled as Dexron/Mercon.
The most common supplier of automatic transmissions now found in European cars is ZF, most of which used Dexron up to the mid-90s, but later require the VW-type ATF-1…
In short, you cannot guess at what is supposed to be in your gearbox.
There are a couple of new fluids: Many VWs and Audis after 1995 are listed as using a AT fluid that lube charts list as “AE”, referencing Esso LT71141. We carry this as VW# G052-162-A2, made by Pentosin in Germany as ATF-1, for $14.95/liter.
Some BMWs 1995–99 are also listed as requiring AE fluid, which does cross-reference to the VW fluid. Later BMWs have sealed transmissions with a 100,000 mile factory fill, so don’t do routine transmission service on these vehicles without BMW’s advice. These BMWs require special equipment and procedures for fluid checking and fill.
Mercedes now has four factory fluids available; check your owner’s manual, and it helps to have the model number off of the transmission.
Some later model Mercedes now do not have a dipstick installed in the transmissions; a dipstick is available for about $40, which you use as a tool but do not leave in the trans. There is a red plastic plug for the dipstick opening that usually breaks when removed, but is fortunately not expensive — and we usually have it in stock.
One new fluid family we are now have available are the special fluids for the CVVT (constantly variable) transmissions.
Chrysler and some of the Japanese manufacturers use a highly friction modified fluid listed as ATF+3 or ATF+4 (AP3 and AP4 on lube charts). You can buy an additive that makes Dexron III meet this specification. There is also a new Ford requirement for Mercon V; again, you can get additives to add to Dexron III for this.
Many of the Japanese manufacturers are now requiring specific fluids; we normally stock (or can get) Toyota and Honda fluids, and can check on others, many of which are a D-4 type which is available from several manufacturers, including Redline and other synthetics.
Amsoil makes a universal synthetic transmission fluid that will work for Dexron, Ford, Mercon V, and the ATF+3 and ATF+4 fluids. It claims superior high and low temperature performance, with three times the service life of petroleum fluids. We have this available at $9.95/qt.
There are other companies that sell a “universal” ATF, but in general, we recommend the specific factory fluids.
Standard transmissions don’t put a lot of stress on the trans fluid (except Minis that run in the engine oil pan), but should be changed according to your owners’ manual. Automatic fluids do run hotter and degrade eventually, but Dexron III is supposed to outlast the old Dexron II.
Most factories recommend changes about every 25–30,000 miles, although some of the later ZF transmissions have 100,000 mile (or “permanent”) recommendations and require special equipment and procedures. There are special manual trans fluids required for many later model cars.