Np Texas, glad you got it sorted out and you didn't have to pay to have it done. It's better to be safe than sorry (and constantly worrying about it haha).

@ Ash8: The problem is most long term forum members are S1 owners who have a completely different transmission. If you read the Miata forums (links I posted above), their long term members mostly seem to aggree that the Motorcraft oil IS better than MT-90. Even so, the MT-90 is certainly good enough for most S2 owners. But if you're like me and really want the smoothest shifting transmission possible, the Motorcraft fluid is worth a try.

I will warn you though, the Motorcraft is twice the price of MT-90, so you really have to want the smoothest transmission to use it. Notchy transmissions are one of my pet peeve's.

 

^ I may likely give that Motorcraft fluid a shot next time I feel my car is due for a change. I don't mind paying extra if the product is better... Wait a sec, I better not start the debate, lol!

 

Sweet, make sure you post a comparison if you do, I wanna know if the Motorcraft is actually worth it haha.

Ill probably do the MT-90 next year just to see.

 

^ It'll be another 10k miles until I change mine again... Until then, I'm enjoying the peace of mind.

 

I changed my transmission(GL4) & rear diff.(GL5 ) with Amsoil at 2,700 miles because my diff. was having that chatter vibration when taking turns. The diff. was really black at 2,700 miles but the transmission was not that bad. I went with Amsoil because it did wonders for my 4Runner. Now, with the oil changes, the car shifts smoother and no more chatter from the diff. I will try the the Redline products for my next change.

 

I have an '04 GT with 48k miles, which I purchased this past Jan. She's my first rotary, and I'm definitely a Honda convert. I love my 8. None of the previous owners have given it the love it really has needed so I've been going down the maintenance list: plugs, coils, wires, and the fluids. I changed the trans and rear diff. with redline fluids, MT-90 for the trans and 75w90 for the rear diff, after reading the praise from others here. Trans shifted amazing right afterwards. I could really feel a difference, which is no surprise since it probably had the original fluid with 43k miles on it. Now about 5k miles after the change, I've really started noticing that it doesn't shift as smoothly. I actually ground second gear the other day, which was a first. Also, I have noticed that on days when it is 90+ degrees out. It is super slick. Even on days with the temp in the mid 70s, I can tell it struggles to go into gears. Thinking motorcraft might be a better option. Anybody else having this problem after switching to redline? Thoughts? Ideas?

 

Redline is great right off the bat but it started getting worse for me as well. Especially on 3 to 2 downshift under hard braking, even with perfect revmatch it would always give me grief. Switched to Eneos and never looked back. Have had 0 problems ever since.

 

Gee this becomes an almost boring topic, done to death...again.

Now, as I see it, with all things being equal, that is Transmission in 1st class condition and Synchronizer Rings (cones), Gears and Bearings included, then look at ambient temperatures and gearbox temps and use.
Again if the car and Tranny only does short driving distances then the owner has the problem not the car or oil.

I don't care what brand of Gear Oil one uses as long as it is GL4 rated, you will be fine.
Each have their own characteristics and operational range/design.

Yes, some brands have different feel and appears to be "a" 'better' product, but again it depends on use will depend just how satisfied one is.

Motorcraft or Ford is a thicker gear oil, so it can give better gear changes on colder boxes, but, when hot I believe thinner is better.

Redline is a thinner gear oil, when stone cold it is a little disappointing, but when gearbox is warm to fully hot operating temps, IMO it is one of the best gear changes and gear oils.

Eneos, Mobil, Shell and BP/Castrol I have not tried/tested, I have stuck with Redline as I like it's performance when my Transmissions are fully hot...both in my RX-8 and Miata/MX-5/Roadster.

 

Noted...

 

noted as well

 

Noted... and added mine with ceratec... half bottle front and other half for diff...

 

Just order some MT 90, 27K miles and just starting to get a rough 5th gear figured i'd start somewhere see if this helps my poor synchro's. Update will follow when i do the change later this week.

 

I used Redline MT90 for a while. Currently I'm back on the stock oil because I had to have the pinion seals on my transmission and differential replaced. I'm not sure if the seal failure has anything to do with the MT90 -- or the Group 5 oil I tried before, which turned out to be too slippery, and possibly reactive with transmission components. In any event, if the shifter feels notchy, an oil change is in order regardless of what you use. Just stay away from Group 5 oils.

 

Yeah it's definitely time for a good fluid change, only 27K but an 04 so it's safe to assume it was never changed. I might as well do the diff as well. I'll wait on coolant since I'm pulling the motor in about a month to work on over winter. Did I read correctly in the diff needs group 5 75W90 correct?

 

Not to jack, does anyone have any bad experiences running Amsoil fluids here on the RX8? On my Evo and s2000, they worked great. I was hoping to use the same brand in the transmission and rear diff. I have a 2009 R3 with almost 25K on the odometer and I was planning to do it either before I put her away for the winter or in spring. Thanks!

 

No NONE, and I also use it on my MX-5 NC2 which has the same (exact) Trans internals as late S2's...I wont use anything but Redline.

Remember MT-90 GL4 for Trans, GL5 for Diff.

Having a Diff Pinion-Axle Seal or Extension Housing Seal leak can happen to anyone, anytime, it's not new.

 

Yes, the amsoil guide clearly states GL4 for the transmission and GL5 75w-90 for the rear differential. They have severe gear and normal and I don't know if one is worse than the other to use. I used severe gear since I was auto-xing or racing...

 

BTW:
I know guys rave about the Motorcraft Trans Fluid in the Miata Forum, however, I only use Redline, in both my P66M Transmissions, my MX-5 Trans is the very latest updated (current) unit made by Mazda (P66M's are a Mazda made trans not AISIN).

Anyway, the smoothness on my 2011 Miata/MX-5 with MT90 is just amazing, it is silky smooth.
No notchyness, no baulking or blocking when cold...when hot it is just a click/click stick movement at any RPM...bliss!!!

The best 6 Speed Manual Trans Mazda has EVER made...

I will say this again, and again, for warm to hot weather climates (like South Australia, Texas), the MT-90 IS the best, as it is not too thick or too thin...it is just right.

Also I know I have said this many times, but the recommended distance on factory (original) Gear Fluids are way too long...from new, change in the first 1000-2000 KMS or Miles, and then halve the recommended Mazda change intervals.

 

I have not had the best shifting S2 transmission ever since I bought it but I have used both the Redline MT90 and now am using the Motorcraft fluid. I gave time for the Motorcraft fluid to break in, just like the Miata guys said to, but I am going to go back to Redline. I agree with ASH. To me, the Redline MT90 was smoother.

 

TRANSMISSION OIL REPLACEMENT
1. Position the vehicle on level ground. 2. Remove oil filler plug and drain plug, and then drain the oil.
3. Clean drain plug. 4. Install drain plug and a new washer.
(w)
RX-8 Transmission (Manual & Auto) Page 24
5.
6.
o 2748 N·m {2.84.9 kgf·m, 2035 ft·lbf} Add the specified amount and type of oil through the plug port for oil filler plug to near the brim of the port.
Tightening torque
Specified oil grade
o API Service GL-4 or GL-5 Specified oil viscosity
o SAE 75W-90 Capacity (approx. quantity)
o 1.75 L {1.85 US qt, 1.54 lmp qt} Install oil filler plug and a new washer.
Tightening torque
o 2748 N·m {2.84.9 kgf·m, 2035 ft·lbf}

This came right from mazda workshop manual for rx8, it says GL-4 or GL-5, I will not put GL-5 in my transmission due to the sulfur but I wanted to point this out.

 

ALWAYS take the filler plug out before the drain - you don't want to drain the box and find the filler is seized and you can't get any oil in.

I tried every GL-4 fluid I could find, but nothing was smoother than Redline MT-90.

I actually mix in about 20%-25% Redline MTL, which is a little 'thinner', and gives me just the best shifts.

 

Just changed my transmission and diff fluid with the Redline products and simply put.

God has parted the heavens and taken an holy leak in my tranny and diff, no other way to really put it. All my previous shift problems are gone feels like a new box, tight and smooth. Would highly recommend this to all 8 owners out there for under 100 bucks and an hour of your time its auto cruelty if you don't do it.

 

YES. I used AMSoil's group 5 gear oil and it didn't work well. (at the time, their website recommended GL5 for the transmission and the diff.) It was too slippery and it prevented the synchronizers' friction surfaces from working properly. (Considering the diff has limited-slip parts in it, I wouldn't use GL5 in the diff either.) Also, there is the slim possibility it contributed to the leaky transmission seals I recently got replaced.

Stick with a group 4 oil.