Need to service your automatic transmission? The market for automatic transmission fluid (ATF) has recently become saturated, if you’ll pardon the pun. There used to be just two choices: Type F for the Blue Oval guys, and GM’s Dexron for just about everything else. Today, Ford alone has seven different automatic transmissions fluids. Splash in Dexron versions III and VI and Chrysler’s +3 and +4 fluids and multiply that by a dozen or so oil companies offering their versions of these fluids and the choices, and the resultant confusion is rampant.
To attempt to make sense of all of this we’ve asked for a little help from our friendly neighborhood tribologist: Lake Speed, Jr. Yes, his dad is NASCAR’s Lake Speed, but more importantly, our Speed is our oil-engineer guide to lead us through this slippery ATF maze.
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What triggered this explosion of boutique fluids is the OE’s search for improved fuel mileage. Each car company has created its own specific lubricant to meet an increasingly narrow set of requirements. Combined with the escalation in the number of gears and different types of automatic transmissions, like continuously variable transmissions that demand a specific fluid, and we find ourselves slogging through an ATF labyrinth.
Adding to the confusion are the many claims that these latest fluids are backwards compatible. The unfortunate part is that this isn’t always true. Let’s offer some specific examples to show how complicated this can become. Let’s look at the GM 4L60E automatic in a 2000 Camaro or Corvette. Dexron VI is often claimed as the proper fill yet Dexron VI didn’t appear until 2005, which means this transmission was originally a factory fill with Dexron III.
This isn’t a huge problem since Dexron VI will certainly work. Looking at these fluids more carefully with Speed’s help, we learned that while Dexron VI is in many ways a better fluid with a more stable viscosity at higher temperature, it is also a lower viscosity fluid, which is the goal now in search of better fuel mileage and to satisfy demands set on the car companies for corporate average fuel economy (CAFE) standards.
It might appear that Dexron VI would therefore be backwards compatible as far back as the older TH350 and TH400 transmissions. The reality is that Dex VI is best only for newer vehicles. Speed tells us that he experimented with using Dexron VI in an older vehicle originally intended for Dexron III and found that the converter’s stall speed increased slightly which is understandable given Dexron VI’s lighter viscosity. This might be advantageous for some applications, but perhaps not for others.
For three-speed autos that date back to the ’60s, the newer fluids generally aren’t an ideal match. Twenty-first century automatics are designed specifically to use fluids with added friction modifiers additives that are intended to soften clutch engagement. The clutch packages in these later transmissions are designed to be compatible with these newer fluids. However, older performance transmissions like a TH350 or TH400, the Torqueflite 727 and 904, or the Ford C4 and C6 would not work as well with these updated fluids.
Attempting to make some sense out of all this, Speed suggested using the calendar year 2000 as a kind of cross-over or watershed point. The plan would be to use the most modern ATF for transmissions built after this calendar date. For automatics built prior to the turn of the century would be to consider using a more traditional fluid.
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Given that, then the next obvious question is what ATF should be used in the older transmissions? Let’s say we’ve built a street-driven big-block Chevelle with monster torque pushing through a built TH400 transmission. The car sees mostly street miles but also spends most weekends at the drag strip. Dexron VI would certainly not hurt the transmission but neither would it be the best plan. This would appear to leave Dexron III as the sole choice. But Speed suggests considering Ford’s Type F fluid for most if not all of these older automatics.
That might seem sacrilegious to the brand loyal believers but the choice has plenty of merit. The original Ford Type F fluid was formulated with a reduced friction modifier package with the goal to create quick clutch engagement and reduce clutch slippage.
GM drag racers have known this trick for decades and have used the Ford Type F fluid to improve shift quality and that’s still a good plan today. Ford’s Type F is still relatively easy to find although not always stocked on shelves at the local auto parts store.
If you’re looking for a very high quality Type F, consider this: ATI has been building torque converts and drag race automatics for decades and recently commissioned Driven Oil to formulate not one but two different versions of the older Type F for drag racing. As outlined in our Parts List, ATI offers both 20 weight and 30 weight versions. A heavy car with lots of torque might choose the 30W style while the lighter fluid could be used in the rest of the applications or to adjust stall speed slightly higher. This is a pure synthetic fluid, which is why it’s slightly more expensive.
Invariably, the question of mixing different types or generations of ATF will come up. Of course, in an emergency, any ATF is better than nothing. But for the discerning enthusiast, it’s important not to mix fluids with different additive packages. This gets back to understanding what all the different labels mean. For example, Chrysler now has a specific +4 fluid that uses a different additive package than both Dexron, and Mercon.
In an attempt to reduce the confusion, many oil companies now market multi-compatible fluids. For example, you’ll see fluids that offer the combination of Dexron and Mercon fluids. The original factory specs for these two fluids is different, but also close enough that a single ATF can achieve both. However, if you see fluids that claim to meet all applications for all vehicles, it’s best to avoid them since the more universal the fluid, the less likely it is that is good for your transmission especially in a performance application. For older automatics, it is especially important to avoid ATFs intended for continuously variable transmissions (CVT) and fluids identified as low viscosity (LV) or ultra-low viscosity (ULV). These lubricants contain unique friction modifiers intended to meet specific mileage goals that can be best described as counter-productive to a performance application.
Synthetic is another term often used with both engine oil and transmission fluid. Essentially this refers to the quality of the base oil. While most of the talk up to this point has focused on additives, the base oil is also critical, especially with regard to temperature stability. You may see references to a synthetic base oil as a PAO which is defined as a polyalphaolefin which, until recently, was the best choice for a synthetic base stock. Recently, Exxon-Mobil has created a new mPAO (metallocine polyalphaolefin) base stock that offers significant improvements as indicated with a higher viscosity index rating.
All this borders on geeking out over petro-chemistry, but if the search is on for the best ATF to use, it would start with a pure synthetic base stock. Within the examples in the Parts List, look for fluids listed as pure synthetics. Among these, Driven AT3 and AT6 fluids use the most recent mPAO base stock, as do fluids from ATI fluids. You will also see the term synthetic blend for certain ATF fluid descriptions. This attempts to improve traditional base oil by adding a percentage of synthetic oil.
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The main advantage to using a synthetic ATF is superior thermal stability. Performance automatics with high-stall converters generate an immense amount of heat. Heat tends to destroy the fluid’s additive packages and reducing their performance, which can result in inconsistency as read on the time slip. On the street, a more stable synthetic ATF will retain its qualities over a longer period of time and be capable of withstanding an occasional high temperature situation while still protecting the transmission from damage. Of course, this improved performance comes at a price.
We’ve discovered that it really pays to shop around when it comes to price. Because most automatics require as many as 14 quarts (especially the 4L80E) depending upon converter size and pan depth, this represents a sizable investment in fluid. One of the more interesting price comparisons we discovered was a quart of AC Delco Dexron VI for sale through a private seller on eBay charging $9.69. With a couple of keystrokes we arrived at RockAuto and found the identical AC Delco ATF for $3.73. If we needed 12 quarts, RockAuto would save us over $70. We found an even egregious example with an Amazon seller asking $12 per quart for Motorcraft Type F while RockAuto would sell us all we wanted for a mere $3.44 per quart. That’s nearly a $9.00 per quart difference!
You can expect the future of automatic transmissions to become an even larger crazy quilt of ATF versions as the OE’s look to improve fuel efficiency with 8 and 10-speed automatics. While that portion of the industry will change, sticking with some tried-and-true fluids for older automatics will certainly make everything much less complex.
In speaking with several automatic transmission builders, the most common mistake that can kill or damage an automatic trans is improper filling. The accepted standard is that, with the engine running and the transmission fully warm, the fluid should be level with the transmission pan rail height. Mixing transmissions and dip sticks can produce an erroneous level.
Taking this one step further, many trans builders including TCI’s Kevin Winstead, the guys at PerformaBuilt automatics, and Lightweight Turbo 400 trans builder John Kilgore all agree that overfilling or exceeding this level for a performance application by roughly to 1 quart for most automatics is far preferable to under-filling. The reason is that hard drag racing launches and high acceleration rates will push a certain amount of fluid into the extension housing and away from the filter/pickup.
If these g-forces uncover the inlet to the filter, line pressure will drop as air is introduced into the hydraulic system. Losing line pressure is the first step towards creating clutch slip on engagement, which can eventually cause the trans to fail.
Obviously, over-filling the transmission to the point where the fluid level contacts the spinning components is also bad since this will quickly aerate the fluid, creating the same problems as insufficient fluid. According to the sources we spoke to, it appears that over-filling by roughly to 1 quart with the trans fully warmed up is acceptable. If the fluid begins to be forced out of the vent at the top of the transmission, this is most often a sign that the level is over-filled.
All these part numbers reference 1-quart containers the price will be slightly lower when purchasing in greater quantities like gallons or case lots. The prices here may only be valid as on-line purchases.
Source: https://t-tees.com
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