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Of all the liquids flowing within your vehicle, none is more important than your automatic transmission fluid. Sure, all liquids matter, but it’s the vital lubricant that keeps the clutches and friction plates within the transmission cool and running smoothly. More than just “oil,” an automatic transmission fluid (ATF) is a complex chemical mix. But is it absolutely vital to get the right type for your vehicle? That is a question I hear quite often, so to get some solid information, I reached out to ATI Performance Products.
It’s Your Type
ATF can be divided into two main types: petroleum (also called traditional) and synthetic. The former is based on natural oils while the latter is based on synthetic polymers. Just as an aside, most new vehicles run a synthetic ATF, and if I were to venture a guess, many classic cars still continue to use a petroleum-based fluid.
If you are asking, “should I use synthetic- or petroleum-based fluid?”, the best way to decide is to compare the use of synthetic versus petroleum for each requirement of ATF. Proper lubrication is the main requirement, and an ATF’s ability to deliver this quality depends on both the base stock and additive’s ability to provide lubrication throughout the complete operating range of the transmission. Transmissions are required to operate in varying ranges of cold to hot, and the thermal properties of synthetics vs. petroleum results in a clear advantage for synthetics. Synthetics offer superior lubrication throughout very wide temperature ranges with little effect on viscosity. However, petroleum-based ATF fluids are not thermally stable, and will “thin” at high temperature and thicken at lower temperatures.
Max Duty Super F
ATI’s 30-weight Max Duty Super F is for large displacement, turbocharged, or very high horsepower engines — including off-road and monster trucks. It features heavier viscosity for less thermal break down, cooler temps, and better converter lock-up over ATI’s 20 weight Super F. Recommended for use in GM Powerglide, Turbo 350 and 400, Chrysler Torqueflite 727 and 904, Ford’s C4, C6, and other non-electronic transmissions.
Hot, Hotter, Burned
It’s no secret that heat will kill a transmission in short order. When both petroleum-based and synthetic fluids are in a liquid state, the heat-transfer ability is very similar. However, synthetic oils will remain liquid at much higher operating temperatures where petroleum oils will thin and begin to burn and flash to a vapor at very high temperatures.
Movement of and engagement of clutches in the transmission is accomplished by pressurized-fluid movement (i.e., hydraulics). When traditional ATF is operating at very high temperatures, the previously mentioned flashing to vapor can occur. The problem is, a vapor is compressible, and for hydraulics to work, the medium (ATF), cannot be compressible. Since synthetic oils will tolerate much higher temperatures than traditional oils, the higher temperature range of synthetics gives it better hydraulic function at those high temperatures. At very low temperatures (i.e, winter in Pennsylvania), petroleum oils are similar to pudding where synthetics are less viscous.
The inside of an automatic transmission is filled with clutch plates and friction discs that come together or separate to move the required planetary gears, creating a moving force to the required gear.
When automatic transmissions were first introduced to the buying public, there was only one ATF meeting the requirements of the American manufacturers. General Motors referred to its ATF as Dexron II and Ford’s specified fluid was labeled Mercon.
Super F
ATI’s Super F transmission fluid is an effective ATF for use in Powerglides, Turbo 350 and 400, Torqueflite 727 and 904, and Ford C4 and C6 automatics. Super F is great for any non-electric transmission. Super F can also be used in high-performance street applications and is excellent for towing use. It can be mixed with petroleum-based ATF without harm, but obviously, the higher the percentage of Super F in the mix, the better the performance and reliability.
According to ATI Performance’s JC Beattie, “In our A/SA Challenger, the Super F fluid was a solid two-hundredths quicker in back-to-back testing over non-synthetic Type F. If I didn’t test it myself, I wouldn’t be telling you this. Over non-synthetic and other synthetics without Type F, you can expect lower heat build-up for more consistent rounds, quicker and firmer shifts, longer life of the fluid, and internal parts, and fewer fluid changes! What more could you ask for?”
The main difference between many of the new ATF lubricants and their predecessors comes down to viscosity. The viscosity of any ATF is measured by Kinematic Viscosity, which is a measure of a fluid’s internal resistance to flow under gravitational forces. It is determined by measuring the time in seconds, that is required for a fixed volume of fluid to flow a known distance (by gravity) through a capillary within a calibrated viscometer at a closely controlled temperature.
The new, modern ATF fluids are manufactured with a lower viscosity, and its kinematic viscosity is typically on the order of 6 centistokes (centimeter-gram-second) at 212 degrees, while the older fluids are in the range of 7.0 to 7.5 centistoke (heavier) at 212 degrees. This lower viscosity helps to improve low-temperature performance and reduce friction to deliver a potential increase in fuel economy. Also, the additive mix in the latest fluids also offers improved oxidation stability, shear stability, and friction durability to provide more consistent shift performance over the life of the fluid.
What Does This Mean For Classic Car Owners?
Among the myriad of fluid choices available, when it comes to most pre-electronic transmissions, the good news is that all the new ATFs are compatible. That means Dexron-VI is safe for use in all GM transmissions back to the beginning. The same is true for Chrysler transmissions calling for ATF+4 (unless Dexron was specified). Ford’s Mercon V is also safe for early transmissions. The only exception is the 1977 to ’81 Ford transmissions that require Type-F fluid.
When is the last time you changed your transmission fluid? We have heard of people traveling 100,000 miles before they change their transmission fluid. That seems like a long time, and most companies recommend no more than 80,000. Look at it this way, is it cheaper to change the fluid or rebuild the transmission?
Since most, if not all, classic Chevys with pre-electronic transmissions can safely use any of the Dexron variants, have you ever considered using Type-F fluid in your classic Chevy? The reason I ask is, Type-F fluid is formulated with a reduced friction modifier package with the goal to create quick clutch engagement and reduce clutch slippage. If that sounds like it will make the transmission perform better, that is because it does. Drag racers and many transmission rebuilders have been utilizing and recommending Type-F for decades to improve shift quality.
Eventually, the question of mixing different types of ATF is asked. It happens, you’re on a trip or at the track, and you have to add fluid. In an emergency, it is safe to say that any ATF is better than nothing, and mixing Dexron and Type-F is not detrimental to your transmission.
If most transmission builders agree that Type-F is a great option for all GM pre-electronic transmissions, which one should you use? Might I suggest you consider this: ATI has been in the performance transmission market for decades, and that means they know a little bit about transmission fluid as well. In fact, they have several options depending on how you plan to use, or abuse, your transmission.
Ultra Low Viscosity Super F
Finally, ATI’s Ultra Low Viscosity Super F is perfect for “lower” horsepower rides — like daily cruisers, and street/strip hot rods. This is a 100-percent PAO-based synthetic and its recommended uses cover GM Powerglide, Turbo 350, Turbo 400, Chrysler’s 904 and 727, Ford’s C4, C6, and other non-electronic transmissions.
