NA Miata - MT and RD fluid

[AngryScientist]

Hard to believe 1990 was 36 years ago!

I just bought the car and the service history is unknown to me, so I'm going through and doing all of the fluids. This is a 1.6 car, so definitely nothing high horsepower.

Couple of questions: When doing the MT and RD fluid with an unknown service history is it recommended to do a "flush" of running a cheaper gear oil for a hundred miles or so to clean out the gearboxes before adding the final lube, or is that totally unnecessary?

If possible I'd like to use the same fluid in both units. Any recommendations? This will be a weekend street driven car. No track days or anything like that. My guess is just about anything will do, but we're all oil geeks here and I would prefer to have the most premium choice, even if it really does not matter

Excuse the mundane question. It's the dead of winter here and I'm overthinking and over-researching before I do some maintenance in the warmer Spring months.

 

[randomhero439]

Assuming the driveline is working with no issues now, I would just do a simple drain and fill with your fluid of choice. Maybe Amsoil products.

Does the manual spec a GL-5 for both the transmission and differential? Or does the transmission need a GL-4.

 

[skyactiv]

Motorcraft XT-M5-QS is highly regarded in the Mazda Miata community. I used it in a VW GTI years ago and the fluid at the time was made in Germany and contained PAO. Read the reviews on Amazon with the one containing 520+ reviews. I bought it at a Ford dealer, was quoted a stupid price and politely said if you can compete with an online seller I'll buy it today.

 

[ctechbob]

Motorcraft XT-M5-QS is highly regarded in the Mazda Miata community. I used it in a VW GTI years ago and the fluid at the time was made in Germany and contained PAO. Read the reviews on Amazon with the one containing 520+ reviews. I bought it at a Ford dealer, was quoted a stupid price and politely said if you can compete with an online seller I'll buy it today.

What he said and a good GL5 in the diff. That's all you really need.

Same fluid for both...you won't like it. The gearbox really needs to be something suited for it (The Motorcraft stuff) and the rear end, being a tiny little 6" gear, needs a good GL5 75W90. Doesn't really matter what, even if you have the VLSD the choice of gear oil won't make any difference to it as it is a sealed unit.

I tried the Mobil 1 Gear lube in my transmission and it was terrible. Swapped it out in under 100 miles for something more suitable.

 

[randomhero439]

I have a friend who drives the hell out of his NA on track for the last 10+ years. He used the Ford Motorcraft XT-M5-QS for the transmission and Amsoil or Mobil 1 75w-90 gear oil for the diff

 

[mzr]

Use a GL4 for the transmission, I always used Redline MTL for the two NAs (1993 and 1996) I had. It helped with engaging second gear when cold. Don't forget to fill the turret. For the differential, Redline 75w90.

 

[GaryMX5]

I and many other Miata owners also used Redline MT90 in the transmission and 75w-90 gl5 in the diff.

 

[ctechbob]

Use a GL4 for the transmission, I always used Redline MTL for the two NAs (1993 and 1996) I had. It helped with engaging second gear when cold. Don't forget to fill the turret. For the differential, Redline 75w90.

And ditch the crappy plastic bushing.

 

[AngryScientist]

Follow-up: Going with Redline MTL in the transmission and GL5 75/90 in the RS.