Install the proper fluid in an automatic transmission because using the wrong type may cause strange symptoms and costly comebacks. Keep these points in mind.
In my last two columns, I discussed the importance of periodically replacing automatic transmission fluid (ATF). Years of field experience suggest that ATF service may be out of sight and out of mind — until automatic transmission symptoms appear.
In all fairness, it may be too late to save an automatic transmission once those symptoms appear.
However, replacing the ATF may solve shifting problems, saving the transmission.
As I explained in my last column, "exchanging" new ATF for the old with a transmission service machine is the most effective way to replace the fluid.
Obviously, tire dealers and service shop operators prefer to buy the fewest number of lubricants and fluids — not to mention purchase them in bulk. Readers have asked me if they can substitute an ATF they already have for an OEM fluid.
The answer is "definitely maybe." The profit margin on a bulk purchase of "generic" ATF may be enticing, but that attractive margin isn't so attractive if the replacement fluid causes performance problems or shortens the life of a transmission.
The only thing I can recommend is to test this multi-purpose ATF in a variety of known-good vehicles. If the transmissions in these vehicles perform to your expectations, then and only then answer a question: "Are you ready to back the product after you install it?"
Mind you, I cannot deliver a comprehensive treatise here on the pros and cons of substituting alternative fluids, but with a small helping of tech talk, I can describe a prime example of problems caused by the incorrect ATF.
All automatic transmissions contain clutch plates. Each clutch is a steel plate lined with friction material. At the appropriate time, transmission fluid pressure "engages" a clutch plate by pushing it against another component.
On the one hand, the fluid pressure must clamp that clutch plate firmly enough against that component to transfer power.
On the other hand, this clutch engagement is finely calibrated to prevent objectionable jerking or jarring sensations.
Typically, transmission fluid formulations are an integral part of the designer's calibration of shift quality. In other words, the relative firmness of the transmission's shifts is a designed-in trait.
Years of experience have confirmed that installing an "alternative" ATF may make an automatic transmission shift noticeably firmer than it originally did.
This additional firmness may appeal to one customer but annoy another one.
Worse yet, the wrong ATF may cause such an abrupt clutch engagement that the driver feels an annoying jerking, banging or shuddering after you replace the fluid.
The only sure fix may be performing a thorough fluid exchange with OEM-specified ATF.
I see three overall options here. One choice is to install an OEM-specific ATF; adjust your price accordingly where necessary.
Another option is to search for a replacement fluid that not only meets OEM specifications as well as performs like it.
A third option is ratifying ATF with an aftermarket additive. Some companies make additives that are supposed to make an ATF mimic the characteristics of an OEM fluid.
Investigate these options. Where appropriate, experiment on known-good vehicles, then choose the option that suits you. Just remember that fluid ain't just fluid.
Full disclosure: I have met the best-informed sources on transmission topics at Automatic Transmission Rebuilders Association (ATRA) conferences.
This October will mark my 26th consecutive appearance presenting electrical seminars at ATRA's annual Powertrain Expo.