This material applies to both the LF (2.0L) and the L3 (2.3L) engined-vehicles.
The American Petroleum Institute (API) Service rating of a transmission oil refers to the amount of extreme pressure (EP) additives it contains. An API Service GL-1 oil contains no EP additives and a GL-4 Service oil contains about 1/2 the additives of a GL-5 Service oil. EP additives are composed mostly of sulfur/phosphorus compounds that can harm yellow metals such as copper or brass that are contained in some synchros. Mazda3 synchros do not contain yellow metals and consequently, as clearly stated in the M/T section of the FSM, either GL-4 or GL-5 oils are completely safe to use. The API service rating is completely independent of the viscosity rating so, for example, an SAE 75W-90 oil could have a GL-4 or a GL-5 or even a GL-1 Service rating.
In point of fact, API categories GL-1, GL-2, GL-3, and GL-6 were declared inactive (obsolete) by an SAE Technical Committee in 1995, although oils may still be marketed with these designations. Concomitantly, ASTM International (American Society for Testing and Materials) does not plan to maintain the performance tests associated with these categories, as in a number of cases these tests can no longer be run because parts or test installations are not available.
On the assumption that most of you reading this want to upgrade from a mineral to a synthetic oil, in addition to listing the transmission oil specs, I'll provide a partial list of fully synthetic oil alternatives that I believe to be true synthetics. In order to qualify, the manufacturer must specify that it is derived from Group IV (PAO) or Group V (Polyol ester) base stocks. It is NOT enough simply to state that the oil is synthetic, fully synthetic or 100% synthetic. After all, Castrol Syntec claims to be fully synthetic, but we all know it to be a hydrocracked mineral oil. I'll focus mostly on Red Line oil because not only is it my brand of choice but, more importantly, they provide more comprehensive data than can be found on other oil company websites.
Manual Transmission (G35M-R)
The capacity is ~ 3.03 quarts (2.87L). The FSM specifies SAE 75W-90 (all season) or SAE 80W-90 if the temperature never falls below 50 deg F (10 deg C). Suitable synthetic replacement oils are as follows:
Amsoil Synthetic Manual Transmission and Transaxle Gear Lube; SAE 75W-90, API GL-4. This is Amsoil's currently recommended oil for this application.
http://www.amsoil.com
Fuchs-Silkolene: Silkolene Silktran SYN 5; SAE 75W-90, API GL-4/5. A fully synthetic M/T oil that, according to the manufacturer, is ideal for road and competition limited-slip differentials. May be used where conventional SAE 90, 85W-90 or 80W-90 lubricants are recommended.
http://www.silkoleneoil.com
Fuchs-Silkolene is a British/German company. For a list of distributors in North America, go to:
http://www.fuchs-oil.com/worldwide.1.html?ziel=9&EN
Motul Gear 300 SAE 75W-90; API GL-5
http://www.motul.com
Motul is a French company with many distributors in North America as a Google search will indicate.
Red Line MT-90; SAE 75W-90, API GL-4. According to Red Line, it has the appropriate coefficient of friction for most manual transmission synchronizers. Red Line claims that many gear oils, engine oils and ATFs are too slippery for proper synchro engagement.
http://www.redlineoil.com
Torco RTF Racing Transmission Fluid: SAE 75W-90; SAE 80W-90; API GL-6. According to the manufacturer, this oil, derived from Group IV/V base stocks, is suitable for both racing and street use. As noted above, API GL-6 is an obsolete classification. It would provide a level of of EP additive protection far in excess of anything our M/Ts currently require.
http://torcooil.com
Automatic Transmissions
FN4A-EL (4-speed)
The capacity is 7.6 quarts (7.2L) after a complete fluid removal. The FSM specifies Type ATF M-V.
FS5A-EL (5-speed)
The capacity is 8.6 quarts (8.14L) after complete fluid removal. Again, the FSM specifies Type ATF M-V.
Suitable synthetic replacement fluids for both types of transmission are as follows:
Amsoil Synthetic Universal Automatic Transmission Fluid; replaces Dexron II and III, Mercon and Mercon V (M-V).
Red Line D4 ATF. Interestingly, this is a GL-4 rated oil, one of the two ATFs I know of that are so rated. According to Red Line, D4 ATF is suitable for use where Dexron III, or Mercon fluids are recommended. It is also designed to satisfy the improved low temperature requirements which will be in the new Dexron IV specification and the improved shear-stability requirements which will be part of the new Mercon specifications.
Red Line D6 ATF. It's designed to be a replacement for Dexron VI, Ford Mercon SP, Toyota WS and M-B NAG-2 fluids. According to Red Line, it provides the best low-temperature shiftability in both A/Ts and M/Ts which require, or can use, ATFs. It is also a GL-4 rated oil which satisfies SAE 70W-75 gear requirements.
Torco HiVis Automatic Transmission Fluid. The manufacturer states that this oil, derived from Group IV/V base stocks, is suitable for both racing and street use. Meets all current Dexron and Mercon requirements as well as that of other types.
Finally, there are other transmission oils marketed as synthetic but I have only listed here those that I believe are true synthetic oils (i.e. those that specify they are derived from either Group IV (PAO) or Group V (Polyol ester) base stocks.
Deletions:
Mobil 1 Synthetic Gear Lube LS 75W-90; API GL-5 and Mobil 1 Synthetic ATF have been removed from our list of M/T and ATF lubes believed to be fully synthetic. Discussions on the various oil forums and revised information on Mobil 1's website indicate that the oil is no longer derived solely from Group IV (PAO) base stocks but rather from hydrocracked Group III petroleum stocks with some PAO stock added as a finishing component to enhance overall performance. Thus Mobil 1 is no longer considered a true synthetic by the standards we're applying here.
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the FN4A-EL 4-speed activematic is the same technology found in the 1.6, 1.5 and 1.4 versions based on the trannies from the 2.0 and 2.3 versions.
Read from the automatic transmission heading especially and compare what Southern Sales telling you or a tranny specialist.