Originally Posted by y8s
did you pull back on your joystick?
Joystick? Aren't we Mr. Highfalutin all of a sudden?
Ain't no joystick what I remember:
incidentally, the equivalent redline GL-4 product is apparently the MT-90 you alluded to above.
They've got three non GL-5 oil listed under the "Gear Oil for Manual Transmissions" section: MT-90, MT-85, and MTL. 75W90 NS claims GL-5 / GL-6 / MT-1, but not GL-4, yet claims that it's "Designed for transmissions and transaxles"
and "Popular in Ferrari, Porsche and Subaru transaxles,"
presumably because it "Contains extreme pressure additives like our 75W90 GL-5 oil, but lacks friction modifiers to balance slipperiness."
I understand what's being said here. Everything that's been said is logical. GL-5 is for hypoid gears, and supposedly contains some sort of Extreme Pressure Additive that either bonds to copper or brass parts (rendering the synchro cones unable to do their job) or just attacks and corrodes these parts outright, depending on who you believe.
And Hustler, bbundy, y8s, I'm not calling y'all liars or even that I doubt what you're saying.
I'd just think that if there was a serious risk of damage to the transmission as a result of running GL-5 lube, or even of the shifting performance of the transmission being degraded even slightly, that Mazda wouldn't be slapping a label under the hood of every new Miata telling you that you can run either GL-4 or GL-5 in the transmission. Even if they just suspected
something very slightly bad could possibly
happen if you ran GL-5, they'd issue a TSB to have a new sticker put under the hood, in order to avoid the risk of having to deal with warranty claims and bad press.
I just went and looked up the owner's manual for the 2010 MX5 at MazdaUSA:
It's been 21 years now, and they're still making the same recommendation.