Discuss What is the best fluid for a T5 Transmission on AllFordMustangs.com, the place for Mustang enthusiasts.
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I'm sure Royal Purple makes something that is probably considered by most to be the best. I use Valoline synthetic fluid in my T5s and it has never failed me. T5s like yours (and mine) use Dexron III/Mercon ATF, not gear oil
i asked this question a while back cause i knew the T5 required DEX/MECON III and i wanted the best stuff. my choices was royal purple gear oil, royal purple syncromesh, royal purple ATF or just the regular dextron/mercon III.
i called royal purple's tech line and found out that the best thing to use would be the RP syncromesh.
One last piece of important information. ALL World Class T-5 use ATF (Dextron III) oil and NOT heavy gear oil or Redline MTL! All NON-World Class T-5 use 50 wt gear oil. (The original Ford/Borg-Warner recommendation back in 1984 was Dextron II. As this is no longer available, we and TREMEC recommend the 50 wt gear oil.) We recommend high quality Synthetic oil as it lasts a long time and over a larger operating temperature. It is important to change the oil in your transmission based on how you use the vehicle. If the vehicle is your daily driver then changing the oil every two to three years is fine. However, if the transmission sees regular track duty and pushed hard, then once or twice a year is in order. When we rebuild transmissions, we can tell when the oil has been changed often as the parts are much cleaner with less over all wear. There is no filter inside the manual transmission only a magnet at the bottom to pick up the metallic particles in the oil, the only metallic parts in a transmission is the gears or bearings. Oil is cheap, transmissions are not!
Definitely, 100%, no doubt, go with the ATF as specified by Ford and Borg-Warner. And no additives.
I haven't seen it yet in this thread, but it never fails, someone will chime in and say "it's a gear box, you gotta put gear lube in it". NO. The World Class T5 was engineered to use ATF, so whatever brand you choose, use ATF. Don't let anyone out there think they know more than the engineers who designed this transmission. As an engineer who designs consumer products, let me just tell you it's just silly when people assume they know more about the transmission than the guy who engineered it.
That being said, the T5 it only takes a couple quarts, and it's not like you change it every day, so spend a few extra bucks and buy the best synthetic ATF you can find. Which is best in this application is largely based on opinion, but I've tried Amsoil and I've also run conventional non-synthetic ATF. I've never had a lubrication-related problem. Let's be honest, most T5's that do fail will break, not wear out. I'm on my third T5 and it's not because I'm a high-school powershifter, or that I don't know how to drive stick. I've been driving stick shift for 30 years. The sad truth is, this transmission was rated by Borg-Warner (now Tremec) for 280 lb-ft of torque... while the 5.0 in the 1987-up Mustangs was rated at 300 lb-ft. And that's before any modifications, of which most of us have done at least a few. So if driven enthusiastically, your T5 may eventually break; and there's nothing any synthetic or magic additives will do to prevent that.
If you want it to last forever, drive like a grown-up, don't powershift, don't put a set of cheater slicks on and go hit your local drag strip, and for cheap insurance, change the ATF in it once a year. On the other hand if you're willing to replace it every now and then, put in any name-brand ATF, drive it like your life depends on winning every stoplight-challenge, and have fun!
Well after surching through the internet for answers on the subject, I went ahead and changed my fluid in the T5 to pinsoil synchromesh. And if you are searching high and low for some answers you just got one. This is by far the best fluid I have ever used it is the consistency of watered down gear oil and boy what a difference in the shift quality. Is is so smooth it feels like a new tranny, seriously its that good.
Sorry ATF you do not belong in a manual transmission.