Haven't seen any threads about this specific to the S2. My transmission has felt just the least bit notchy lately so I think I'm gonna change the fluid within the next few weeks. I'm at ~14k miles. The maintenance schedule doesn't suggest changing it until 30k miles, but my car has seen a few track days and I shift VERY aggressively at the track. I've been doing a little research today, here's what I've found.


S1 owners: The most highly recommended oil seems to be Redline MT-90, with Royal Purple (not sure on exact oil) being a less-recommened alternative along with Eneos 75w90, which is recommended by the always reputable BHR guys.

These two threads are mostly whre that info came from:
https://www.rx8club.com/series-i-do-yourself-forum-73/diy-transmission-differential-fluid-replacement-35115/
https://www.rx8club.com/series-i-tech-garage-22/royal-purple-manual-transmission-fluid-193286/


Miata owners: Remembering that I've read S2's share their transmission with the newer Miata, I decided to look for their opinions. It seems Redline MT-90 used to be the popular thing there too, but now Ford Motorcraft Synthetic ("XT-M5-QS"??) is all the rage and seems highly recommended.

Reference Info:
http://forum.miata.net/vb/showthread.php?t=368329
http://forum.miata.net/vb/showthread.php?t=383297
http://forum.miata.net/vb/showthread.php?t=368329


Thoughts/opinions? I'm highly tempted to go with the the Ford Motorcraft after reading all the love from the Miata guys. I didn't find a DIY on the Miata forums, but it seems pretty straight forward and pretty much the same as the S1 DIY. There are some pics of the drain/fill holes scattered around those Miata threads so those will help. I'll try to write a DIY if I do end up doing this myself.

 

MT-90 is a pretty good oil. I use it in my Wrangler, shifts pretty smooth even at 132k miles.

 

I'm using Redline MTL and it's good once it's warmed up. I may switch to the slightly thicker MT-90

 

Don't use Royal Purple. I've used both Redline and Eneos in my S1, but the Motorcraft sounds great. I think your reasoning in following the Miata guys is sound.

Also, it is a good idea to change early on the first interval. More wear happens on break-in, you can expect iron on the drain plug and plenty of yellow metal in the fluid. You might consider running a cheaper fluid, maybe Pennzoil, for a hundred miles as flush before you put in the good stuff. Probably a touch obsessive though.

 

I'm at 12K miles now and I initially switched over at 2K miles with MT90 (I'm now on my second fill with the Redline fluid). No problems here with shifting and I've got 12-15 track days on the car.

 

I'm at 27k miles and want to change mine, just not sure if I can right now. most people recommend using ramps and then jacking up the other end, which isn't possible for me currently.

When I do finally get to change it I think I will go with the motorcraft from all the love it gets on the miata forums.

 

I've heard that you can't fill through the shifter in S2s, anyone know for sure? Because if you do it that way, you don't need to jack up both ends. You could try parking the nose on a sidewalk and the back in the street, if you only have one set of jackstands. I've seen people doing that.

 

I couldn't do that here but its a good idea, and yes as far as I know you can only fill from underneath at the fill hole not thru the shifter.

 

A few days ago (and at just over 9k miles) I had my local Rotary Performance shop change my transmission oil, differential oil, and also flush my brake fluid completely. The shop used Idemitsu 75w90 for both the transmission and differential.

I was having the same experience as the OP... The shifting quality had become a bit more notchy and less smooth. After the service, I feel a positive difference in the shifting quality & feel so far.

 

Well I decided to use my Jeep as a test bed for the Motorcraft fluid (also as practice since this is my first time changing tranny fluid). Redline MT-90 is also the most recommended fluid for the Jeep so I figured the Motorcraft would work well in the Jeep as well. Wow was that an expensive test though! It was $85 for 4 quarts!.

After the change I took my Jeep for a quick test drive and I didn't think there was any really noticeable change. However my Jeep has a terrible transmission and there is only so much a fluid change could do for it. I also didn't have a chance to get the transmission really hot, when the real problems actually show up. I'm taking my Jeep wheeling this weekend though so that should be a better test of the fluid.

 

ALL the RX-8's Series 1 or 2 use the same Oil's, BUT...

The Oil for the Diff and Transmission is NOT the same, one is GL4 and the other is GL5.

Your "shop" is WRONG by using Idemitsu 75w90 for BOTH.

I use REDLINE...
MT-90 GL4 75W90 for Transmission.
75W90 GL5 High Performance Gear Oil for Differential.

They (shop) have used a GL5 in your Tranny...WRONG!...get it out ASAP.

 

Alright, I've just gotta know, what is the Rx8 supposed to use for viscosity? My FSM here says 75w90 for the Transmission, and 90w for the differential, which is backwards of what it seems like most say on here.

Plus, with what I work on personally, they get 30w in the transmission, and 50w in the diff's, which follows that same idea of the transmission getting the lower viscosity.

Hell, I've been searching this for weeks, but every time I flip over to my FSM, I just don't get it. Is this FSM wrong or something? What does it get straight from the factory?

I'm no stranger to this all, I'm just confused as to why I'm reading so many different freaking things.

I know the diff gets stuff strictly for LSD and whatnot, I'm just wondering why there are so many different things said, that's it.




https://www.rx8club.com/showpost.php...8&postcount=85

Just kind of what I'm talking about..

I know the one is GL-4, the other is GL-5, but I've read quite a few people clearly state 75w90 in the Diff, and 90w in the trans. Is that just people being confused about the name or something?

 

how many qts does the tranny take and how many qts does the differential take?

 

Check the DIY I wrote:
https://www.rx8club.com/series-ii-diy-161/diy-series-ii-manual-transmission-fluid-change-217642/

Just to be nice the transmission is 2.06 quarts (2 will probably do it). Not sure about the diff, check your owner's manual it says.

 

Thanks for being nice

 

You are getting a bit confused by the specs - the Redline MT-90 that people use in the tranny IS a 75w90 oil. So it's not 90w.

And then GL-5 rated 75w90 in the diff.

I think the tranny is too stiff with 75w90, so I am the guy from that thread that uses a little Redline MTL, which is rated 75w80, but seems much thinner (makes no sense!)

I heard the 2006 manual actually says 75w80 if you can't find 75w90.....

But get the GL-5 rated oil for the rear end, tends to be very slippery, due to additives that contain sulphur. These same compounds can attack brass/copper etc. which are in the gearbox. So the specs call for "GL4" for the box. Basically the same stuff, but no sulphur.

 

Sorry, got a bit delayed in reading your response. I'll call the local rotary performance shop (which I used) tomorrow if possible. I'm hoping that I was the one who was mistaken and misunderstood them, and they actually used the correct type... Since these details are still new to me, as you probably can presume. I'll clarify with them and then update this thread.

Don't know why, but my 8 is still running top-notch as of now.

 

Alright, Ash.

I called my local rotary shop up first thing this morning, and he said that he would do some further research.

I spoke to him after his research at the end of the day, and he mentioned that the GL4 is designed for lighter transmission loads, and it's the one that is recommended for the RX-8 from Mazda. The GL5 on the other hand, is designed for heavier transmission loads, which shouldn't be a bad thing at all.

The gentleman who operates the shop uses the same GL5 on his own RX-8, and also all his other RX versions.

After I looked into all this, I'm not as motivated to react on changing it out for the GL4. I don't feel any drawback in shifting feel and performance through these past few months.

If it's something that I really should stress about, please let me know.

 

I love those people who think they are smarter than the engineers who designed the car.

Why would Mazda bother to stock and spec TWO different 75w90 oils? Makes no sense at all.

The GL-5 is definitely more 'heavy duty'.
It has sulphur additives for extreme duty.
These additives are excellent lubes and make oils slipperier than a greased eel.
And they will eat the brass/bronze synchronizers right out of your gearbox.

It will run very smoothly, and shift like butter - right up until you hear the crunch and you are back here explaining that 'it won't go into second at all'........

GL-5 rear end

GL-4 gearbox

 

Well frankly, I totally agree with Stealth..
Why would Mazda JAPAN stipulate two separate 75W90 GEAR oils??

And again I don't give a crap what some "rotary" shop says, they like all the others are not Official Mazda Dealers nor do they receive ANY official notifications concerning the product, nor do they officially represent Mazda in anyway..everyone is an expert until something goes wrong.

From memory, I don't think older Mazda's with different transmission designs use GL4's...I could be wrong without checking..but that is not the issue.

If you have the time READ back in this thread to "others" who have gone against Mazda recommendations and to those who have had G/Box issues using the wrong rated or spec gear oils.

EDIT:, Sorry, Not this thread, but there is one around here somewhere....

Anyway Texas, if I was you I would have it changed out.

 

I see. Thanks for the care and help, guys.

Well, I don't want this to bother me (especially because I have a sensitive personailty, lol).

I definitely would not want to ignore advice from two of our veteran forum members here, and I realize that you both wish the best for us RX-8 owners.

I may very likely go ahead and opt to be on the safe side, and switch over to what you use, Ash:

Redline MT-90 GL4 75W90 for Transmission.
Redline 75W90 GL5 High Performance Gear Oil for Differential

I had my brake fluid changed to ATE Super Blue that last time, but I'll go ahead and switch over to Motul RBF 600 this time around, since I heard the Motul is better.

Hopefully the sulpher additives in the GL5 did not negatively affect my transmission during the past 2 months.

I'll give you all another update once I figure my way out here.

Boy, do I dislike stress... Now I have an ugly PIMPLE! Haha!

 

Texas, I agree with Stealth and Ash, you should deffinitely get that GL5 out of your transmission. The posts on those Miata forums (same transmission as us) are all pretty adament about not using GL-5.

On a side note, you might want to try the Motorcraft Full Synthetic I was talking about earlier instead of the Redline MT-90. My transmission is SOO smooth right now with that stuff in it, its amazing! At first it wasn't much of a difference but it has gotten noticably smoother after a month or two (the Miata posts said this would happen). I highly recommend this transmission fluid now! It also seems to like warmer temperatures a lot.

Also check out my DIY if you want to save some cash and not deal with that ignorant repair shop again, it's seriously just as easy as an oil change, maybe even easier.

 

I suggest which brand product long term forum members use are or should be the recommended ones...it is tried and proven...long term.

Most are all synthetic..

 

You could definitely give the motorcraft oil a try, from what I have read it seems the miata people with the same transmission as us all love it.

 

Thank you for all the support. Means very much, for sure!

Well, I didn't get a chance earlier to read the last few posts above me which suggested the Motorcraft fluid, therefore I picked up the Redline MT-90 GL4 75W90 Manual Transmission Fluid from another local shop near me. As soon as I picked up both quarts, I headed over to the rotary shop and had it changed. They didn't take a penny from me, and were positive about changing it for me. I only got the transmission oil changed, and didn't worry about anything else for the time being. I think I'll be okay now.

I'm not upset with the rotary shop, and I know that they had all good intentions for me. I don't really want to knock them, especially because they are a very fair business once you get to know them. At the end, I have no regrets using them and I'll be happy to use them again in the future... I'll just do more research on what they are willing to use and what I should be using, and may bring my own fluid next time if needed.

At the end, I got it changed out to the GL4 version for sure. Two quarts of it was just barely enough (only a tad bit left afterwards), and it costed me about $30 total... That's nothing compared to the sigh of relief I feel now.

Thanks again for the excellent help, everyone!