Miata gearbox oil

[MiataSteve]

I bought some RedLine MTL for the gear box. I read the label which made unsure if it got the "best" type for my old 90 Miata (original trans, never opened 145,000 miles). So, I did a quick search on miata.net and the SpecMiata site. Now I really have a headache. I get better answers here. What is the "right" stuff to fill the tranny with?

[Dave_G]

Red Line MT-90 is probably a little better than MTL for a Miata tranny. They're essentially the same oil, but the MTL is 75W80 and the MT-90 is 75W90. Since Mazda specifies 75W90, I use MT-90. But I would think that either one would work fine. Both of them are GL-4 oils, which is better than the more common GL-5 gear oils because it is less slippery, leading to better performance of the synchros.

I know all this to be true because I've read it on the Internet.

[Stynger]

FWIW I've always used MTL when using Redline products for the Miata trans.

[WillM]

What Les said, or step up to Royal Purple.

Syncromax in the tranny, Max-Gear in the diff.

[MiataSteve]

Thanks Guys!