zenmoused

Hey guys, awesome thread! I am waiting until I get to 1500 miles to do my tranny/diff fluid change, just to make sure I grind as much of the extra metally crap from work-in before I drain it. Just wondering, I see a lot of you used Red Line, and only some use Royal Purple. How did you guys make your decision as to what brand to use? Is one higher performance than the other?

Go48

In my case it was based on previous experience with Red Line and availability at my favorite race shop. I doubt whether anyone on here has done an exhaustive comparison if that's the information you're looking for, but maybe that information is available somewhere on the web.

beachdog

The initial posters used Red Line. Also some of us called Red Line and Royal Purple and Red Line knew exactly which products to use for the RX8 and Royal Purple had to call back later. Of course this was over 2 years ago.

zenmoused

Okay, so really no tests to compare them, but they're both premium as far as everyone's concerned? RP has a big explanation on their site of how well their engine oil works in rotaries- I wonder why they'd be so uncertain about tranny oil? Well, any advantage towards the RP side I'm sure would be minimal (if any), and Red Line seems tried and proven. I'll throw some of that in when the miles roll around. Thanks for your replies!

msrecant

I used Red Line in my Miata based on a number of reports that it smoothed shifting, which it did substantially. While I was originally not going to put Red Line in my RX-8 (it was pretty smooth to begin with), when I had the dealer do a tran/diff fluid replacement at 3K mile (to flush out) I was very unhappy with the how the transmission shifted afterwards. The Red Line absolutely fixed the problem and, I believe, improved on the shifting from the way the car came from the factory.

Note, I did not use the Red Line based on a belief that it is "better" for the transmission and that the tranny will last longer. It was stricly based on the improved shifting characteristics. My take is that any quality gear oil of the appropriate grade will do fine for the expected lifetime of my 8, particularly since it is my daily drive and will probably never see a track or autocross event.

I have never used RP, but based on comments here it sounds like it does the same thing.

MADIZM

Using Redline in my old WRX was a nightmare. Oil was too "slippery" which wouldn't let the synchros work correctly and caused the gears to grind when downshifting.

Big_Mike_4488

Alright, I'm about to order my fluids and washers from Rosenthal. One question first. I asked the Rosenthal Mazda people about how many quarts of each fluid I should buy. I was under the assumption that I only needed two of each since neither the tranny or diff. is more than 2 quarts, but they said somethin about most 8 owners buying three bottles of the tranny fluid and two of the diff. Is this correct or do I only need two bottles of each? Thanks!

MadDashRX8

Only two of each. 1.8 qts tranny, 1.4 qts rear diff. Unless the mechanic spills it all over himself while refilling, two is more than enough.

deamicls

iTrader: (1)

So, I should get 2 of the MT90 and 2 of the 75w90 and put one of one of each in the diff and trans?

MadDashRX8

Nope, not quite. Get two quarts of each type of fluid (4 qts total). Put 1.8 qts of MT90 in the tranny, and 1.4 qts of 75W90 in the rear differential.

willhave8

Okay all. Went to local shop to arrange for them to do a variety of work for me - such as change tranny\diff fluids to redline... I was asked what the clutch\synchros etc were made of and whether or not I knew that the redline fluids would not over time degrade performance by attacking those materials... Well, i said, people on the forum do it all the time. To which you can imagine his response... something to do with lemmings...

So, to the tech heads here, are there any materials issues that we may not have thought of with the use of Redline fluids in our tranny\diff??

This shop has a long record of creating competition Porsche and other cars for over 20 years and knows what they are talking about. He does not want do the work without knowing it will not create long term issues. I am okay with that.

deamicls

iTrader: (1)

I thought that someone mentioned using MTL for the tranny? I think that the person used MTL and MT90 for tranny. Is this not recommended?

StealthTL

iTrader: (1)

The specs call for "GL5" fluid in the rear end, tends to be very slippery, due to additives that contain sulphur. These same compounds can attack brass/copper etc. which may be used in the gearbox. So the specs call for "GL4" for the box. Basically the same stuff, but no sulphur.

I don't think Redline uses the sulphur additives any more, but to be safe, always go with the rating on the bottles.

I personally use a bit (30%/40%)of MTL in with my MT90, found it made a huge difference to the shifting feel.
Not recommending, just saying what worked for me.

S

QBallz

GL4 or GL5 can be used in the gear box according to manual, but only GL5 can be used in the LSD.

willhave8

Thanks for the clarification guys. Going with the Redline MT90 GL-4 for the tranny and 75W90NS GL-5 for the differential.

rx8atlast

If I remember correctly, somewhere in this thread it states to use 75W90, not 75W90NS

QBallz

You dont want to use Redline 75W90NS in your differential because it doesn't have the Limited Slip friction modifiers.

willhave8

I just looked at the bottle and it says Redline 75W90. There are no markings that say 'NS' on it. I think I'm good.

dsmdriver

iTrader: (3)

I just put a RP shifter in my car, and because of this, I still have the center console cover off.

I started thinking- can you fill the tranny from inside the car? When you put the shifter in, you can basically see right into the tranny. If I drain out all of the fluid, put the drain plug back in, and then pour fluid into the shifter hole will this work?

I used to do this all the time with my DSM tranny- there was a bolt on the top that you could take out and fill the tranny from instead of using the "fill hole."

Of course, I'm still talking about taking out the fill plug to figure out when it's full, but putting the fluid in from the top instead of side, which seems much easier and less messy. Has anyone tried this or know enough about the insides of the transmission to know if it will work?

deamicls

iTrader: (1)

It sounds to me like adding some MTL to the MT-90 oil will smooth out the shifting. Is this safe to do? How much is too much? I was thinking of going one and half MT-90 and the rest MTL.

willhave8

Update - My Redline fluids are in. MT90 in the tranny and 75W90 in the differential. First impressions are that I don't hear the chattering when I am sitting in the driveway idling in neutral. Things are much quieter now. Feels great on the road but as others have said before, it already felt good.

gonnahanvan8

I put the Red Line stuff in today. I love it. I followed the directions using the 1/2" tubeing. It worked fabulous. The only thing I would do different next time is wear latex gloves. That gear oil smell is hard to get rid of off your skin. Thx for the DIY.

By the way the notcheyness is gone and my coffee warmer is now much cooler. I took a long trip today and it's posible I'm getting a smidgen better gas milage too.

Waaaahoooooooo!

Rootski

iTrader: (1)

Just to verify, the tranny and differential hold 1.8 and 1.4 quarts respectively, correct?

Also, how many washers do I need? Rosenthal Mazda lists \"Transmission Seal Front\" and \"Transmission Seal Rear\"... are these what I need?. I only count two types of washers, but there\'s 4 holes total. Unless I\'m completely off the trail and need a whole different washer animal... somebody help me out.

What do you recommend, redline MTL or redline MT-90?

Go48

That's what the manual says, but the amount you will put in may be less than that due to the amount of oil left in the nooks and crannies.

I think their "logic" is something like, you only need to replace the drain plug washers/gaskets with new ones, you reuse the fill plug washers/gaskets. Apparently the thinking is that the fill plugs will not leak (much) because the oil is not in continuous contact with the entire opening like the drain plugs openings. I don't agree with that logic, so I replaced all 4 washers as I recall.

MTL is 75W80 and MT-90 is 75W90. The latter is closer to the recommended oil. Incidently,if you have the limited-slip differential, use 75W90--do not use 75W90NS. NS lacks certain aditives for LDDs.

gonnahanvan8

I put MT-90 in my trans and 75W90 in the diff. I replaced all 4 washers. Also, note the socket sizes 23mm and 24mm. Most peeps don't have these, you will need them. Also, deep wells won't fit.