PHeller UberDork
11/6/13 3:49 p.m.

I've tried reading some threads on various fluids for the Miata, but most are either far too long with no relevant information in the first or last pages, or outdated.

Could someone make up a list of various fluids that will work in transmissions and diffs of the Miata, how much to use, how much they cost, and where to find them?

EvanB PowerDork
11/6/13 3:54 p.m.

75W-90 gear oil.

Keith Tanner
Keith Tanner MegaDork
11/6/13 4:09 p.m.

Redline MTL is the best trans fluid for a street car. It's been a favorite of Miata drivers for a couple of decades.

Redline MT90 is a good trans fluid for a race car. Not as friendly when cold as MTL.

Redline 75W-90 for the diff.

All are available at Flyin' Miata. 6-speeds need two quarts of trans fluids, 5-speeds need two quarts plus a bit more for the shifter turret. The latter isn't a high stress location, so you could use just about anything.

BoxheadTim PowerDork
11/6/13 4:09 p.m.

Redline MTL makes a big difference in the transmission. Can't quite remember how much the transmission takes (I think you need to buy 3qts, but I might be off by one here). I just drive to my local Summit Racing and buy it off the shelf there (~$16 a bottle).

IIRC Keith mentioned at some point that their heavier gearbox oil (MT90?) might be better for track use.

BoxheadTim PowerDork
11/6/13 4:10 p.m.


I guess I should have hit "Add Post" sooner .

Kenny_McCormic UltraDork
11/6/13 5:04 p.m.

Redline also makes MT85 now IIRC, if you want to go inbetween. I put the MT90 in my FWD Corolla that calls for 85 or 90 depending on who/what continent you ask and it shifts, uh, sporadically? till it warms up a bit.

PHeller UberDork
11/7/13 7:48 a.m.

What about a cheaper but satisfactory transmission fluid?

Swank Force One
Swank Force One MegaDork
11/7/13 8:26 a.m.

I use Amsoil MTG in the trans, SVG in the diff. I previously had Redline MTL in the trans and Redline 75w-90 in the diff.

The trans felt god-awful. Butter with the Amsoil.

A lot of people are liking the Ford Motorcraft stuff.

Keith Tanner
Keith Tanner MegaDork
11/7/13 10:16 a.m.
PHeller wrote: What about a cheaper but satisfactory transmission fluid?

You're not willing to spend $30 every 30,000 miles with guys who give you tech support?

I'm sure Walmart has something in a big jug.

Swank Force One
Swank Force One MegaDork
11/7/13 10:49 a.m.

Yeah, the Amsoil stuff was something like $15/qt. I'm perfectly ok with $45 every year or two.

RoadWarrior Reader
11/13/13 12:49 a.m.

I've been running Motorcraft Full Synthetic Manual Trans fluid in my gearbox for my '94, it's the currently darling of and I guess S2k guys with notchy gearboxes love it too. All I know is it's done wonders to mine. And seems to do well no matter what temperature the car is at. As to the rear diff, I'm just running regular ol' 75w90 there.

SnowMongoose HalfDork
11/13/13 1:12 a.m.

I bought my Redline MTL from Keith and the folks at FM after nobody within 50 or so miles of me carried it.
I dig it.
(DD, occasional autocross, '95 5-speed)

kylini Reader
11/13/13 4:27 p.m.

I've also had very good experiences with the Motorcraft Full Synthetic, but Redline is cheaper, which is terrifying.

Heck, just changing it will be an improvement!

mistanfo UltraDork
11/14/13 6:04 p.m.

I am a big fan of Redline, Keith's recommendations are spot on. I know a few racers that use the Shockproof in the transmission, but they change it after every race weekend. Now that gets expensive fast! I've always been happy with MTL and 75/90, the shockproof DID shift nicer for a short while, but then got notchy. That's when I found out it's considered a short term solution... Lesson learned. In the turret of a 5 speed, I use whatever oil I have a bit of lying around in a bottle.

Double_Wishbone Reader
11/19/13 10:45 p.m.

I just bought some Redline for my differential, from FM. Happy with it, but not sure if I'd "feel" a difference using lesser fluid, but its a nice insurance policy.

For the transmission, I used Motorcraft Synthetic and it's great. Unfortunately, I can't compare it to Redline since I've never used it, and Motorcraft is more expensive than the Redline. If you google around like I did, though, you can find it for quite a bit cheaper than most places sell it for.

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