Changing tranny fluid

[CosmosMpower]

That's a clue; you don't need oil as thick as you think you do.

Feel free to argue with chief engineers at Honda/Lotus/Mazda. I'm sure they don't know what they're talking about when they engineered the fluid and printed the required oil type/viscosity

[ozone42]

It's about time for me to attempt this again as well. With colder weather here shifting is getting notchy until it's nicely warmed up.

[Snowdoggie]

So what's the best stuff to put in the transmission? Royal Purple? Some special slick shifting racer juice?

[Darron65]

So what's the best stuff to put in the transmission? Royal Purple? Some special slick shifting racer juice?

Redline MTL for me. I've been using it in practically everything since 95 or 96. Nice light shift effort even in cold temperatures. Runs on the low side of viscosity recommendations but still meets manufacturer's specs, Cosmos. The only lighter oil I would consider using is ATF but I'm happy where I'm at.

Viscosity grade is the single most important consideration, followed by additive type/package. I tend to favor lower viscosities as it suits my driving style/duty cycle. If you are pumping twice the original power through your transmission and/or have long track sessions with poor cooling airflow then you may want to run a bit thicker. It's easy to overcompensate in this area though. Install temperature sensors if you really want to know what's going on.

[cam76034]

Feel free to argue with chief engineers at Honda/Lotus/Mazda. I'm sure they don't know what they're talking about when they engineered the fluid and printed the required oil type/viscosity

Funny you should mention this. Take a look at the recommended oil viscosities from a 90 Miata owner's manual versus a 91.

[SirHustlerEsq]

redline mt-90 is too thin for the track, and too thin for the street from personal experience. I started to lose a 3rd gear synchro with mobile 1, and I also found out that it "rolls" more than most.

Motul is the shznit according to BITOG, Gary and Wagz run it and like it. It shifts fine, and the ester compounds in Motul are the best available. BITOG also really likes Shaeffer gear oil, and they've done the testing to prove it. I'd like to run Schaeffer in my 5-speed but can't find it in town. If you track the car, don't expect standard-service oils to do the job of a race-quality oil.