ZumeZume

I purchased MT-90 GL4 for the transmission as I understand it GL5 can damage syncros over time. That gear oil is 75w90 and I searched through a bunch of threads regarding differential fluid and it seems MT-90 is also recommended. However there is a GL4 and GL5 available at the shop I shop at but I cannot seem to find a clear answer to whether or not I need a GL4 or GL5 or if it matters and why? Are the differential gears coated the same as the trans?

Reoze

Officially it's -
GL4 in the tranny
GL5 in the diff

Some people run certain types of GL5 in the transmission, but this is something you would want to spend quite a bit of time researching. As well as making absolutely sure you know what is going in there. Which generally means doing it yourself.

ZumeZume

The official answer was what I was looking for thanks! And it's a good thing it's GL5 the shop I use is the only redline dealer in my city when I bought my GL4 fluid the other day they were the last 2. They had alot of GL5 on the shelf so now I can do everything tomorrow : )

Steve Dallas

Redline MT-90 in the trans (MT-L if you don't track it)
Redline 75W90 in the diff

The GL information is all in the owner's manual.

ZumeZume

Here we go again Steve... I know it's in the owners manual I posted here because there are things that rx8 owners have learned over time that conflict with the owners manual or at least trial and error has showed a better way... and it can never hurt to find out what people are learning works best these days.

Steve Dallas

Oops. Sorry. Did not realize it was you. I'll be sure to refrain from helping you in the future. My mistake. Eh.

ZumeZume

Thanks I would greatly appreciate that

40w8

Diff is goof proof unlike the transmission.

I run Mobil 1 75w90 synthetic.

I drained at 3500 miles to see if any metal.

Sure enough it had about one ounce of silver metal "mud".

I put in a little over 1 bottle of 75w90, then, changed again at 22k miles which had just a trace of that "mud".

Since I drive less than 5k miles/year, I'll probably never change again.

ZumeZume

Thanks you nailed it for me... just bought a nice rx8 with 45k miles but everything previous to my ownership I call " mystery milage " so all engine and gears oils get changed... and changed again shortly thereafter. Up here in Canada at least the average car owner doesn't change tranny and diff fluid anywhere near often enough. It drives me nuts when I buy a car or truck until all fluids for moving parts are changed twice in short order to elaminate as much residue from potential neglect as possible.
Just did second oil and filter change this morning after only 100 miles since the first a week or so ago. Sure enough... it was really black with a bit of a whitish haze. This second oil change I got just over 5 liters out getting some from the oil coolers this time but I see I didn't drop either side low enough for a full drain. I'll get it next change and since I'm a nut about changing oil that will be at the next 1k mile mark at the most. My mechanic says I'm nuts! lol
Thanks again for the info.

IamFodi

iTrader: (1)

He basically gave you the same information you got from the post you said "thanks" for -- except he also went the extra mile to specify exactly which Red Line products match your needs.

Also, he knows a damn sight more about this car than most people here. If you really don't like his advice, that's perfectly alright; I'd suggest ignoring it rather than chastising him because next time, you might have a question that he's one of the very few people who can answer.


Regarding GL ratings:

The difference between GL-4 and GL-5 is basically how much extreme pressure the oil can take. GL-5 oils can take more extreme pressure, usually because they have higher levels of extreme pressure (EP) additives. Those additives are good for protecting gear teeth, but tend to be more corrosive to soft metals, like in synchros.

Our transmissions don't need GL-5 levels of protection, and they have synchros.

Differentials do need GL-5 levels of protection, and they don't have synchros.

So: GL-4 in the trans, GL-5 in the diff.

UnknownJinX

While I do maintenance on my cars and keep an eye on it, I don't usually go that far.

You are absolutely right about cars at the dealership, haha. I remember I had to change so many fluids on my Accord when I first got it from the dealership.

With the engine oil, which kind do you use? I personally just stick with conventional in the RX-8 since that's what Mazda recommends. If you use synthetic, most of them basically cleans as they run through the engine. Good quality conventional aren't too shabby, either.

I wouldn't worry too much about the color - engine oil can get dark quickly regardless of the condition of the engine. The whitish haze may just be condensation. All you gotta do is take the car out for a nice long drive on the highway.

Also, premixing will help.

wannawankel

I use SAE rated SN grade 5W20 and recently switched to 5W30. I buy whatever is cheapest AND labeled meets SAE SN. I change the engine oil often ~1000-2000 miles and also test the oil on occasion with a reputable oil testing firm.

I recently changed @ 45K miles my MT (Redline MT-90 though others say MTL is better - both are only GL-4 rated) and diff fluid (Redline 75W90 GL-5 rated).

TheWyvern

I recently acquired my 8 back in December and I have yet to change the differential and M/T fluid. How often would you guys recommend doing so? I've only put 5-6k miles on the car, but as ZumeZume says the 70k miles before this are mystery miles so it may be a good idea. The knowledge base here on the forum seems to suggest everything between 20k, 30k, and even 35k.

Steve Dallas

There is nothing wrong with MT-90. I use it in my 8's 6 speed and in my Miata's 5 speed. Some people have a niggling complaint that the transmission feels notchy until it is fully up to temperature. Colder climates are notchy-er than warmer climates. Both of my cars exhibit this characteristic, but it doesn't bother me. MT-L is smooth in all but the most extreme low temperatures. Choose based on your application and preferences. The basic rule of thumb is, MT-90 for track use and MT-L for street use. But, plenty of people use MT-90 on the street just fine.

Edit: Be aware that MT-L is a 75W80 oil, which is thinner than Mazda's recommended 75W90 oil. Use it at your own risk.

In a brand new, street driven car, I change it at 1K miles, then every 50-60K miles. If you use a quality synthetic oil, that interval is plenty good enough. If your car has 70K on the clock, I would assume it has never been changed and change it soon. Then relax.

As for motor oil, use whatever makes you happy. Drain and fill every 3K miles and change the filter every 6K miles. You'll be fine.

.

TheWyvern

Thanks, Steve. Yeah I've been keeping up with the oil, probably moreso than I need to. 10w30 RP Full Synth every 2k since I bought the car, and 5-6oz of Idemitsu in every full fill up.

I had pretty much assumed it's never been done, so I'll get myself some redline and change both the differential and the trans this coming weekend. You'd recommend another full change in 50k, then?

Steve Dallas

There is a thread on here somewhere, wherein people post their Used Oil Analysis results from Blackstone Labs. According to those results, Royal Purple motor oil performs shockingly poorly in some key metrics. Mobil 1, Pennzoil Ultra, Valvoline Synpower, etc. all outperform RP in viscosity stability, believe it or not. So, you can save some money there and just buy one of the normal synthetics, if you are so inclined.

There is nothing special about our transmissions or differentials that require their oils to be changed any more frequently than listed in the owner's manual. IIRC, Schedule 1 calls for every 60K miles, and Schedule 2 calls for every 30K miles. If your situation conforms to Schedule 1, and you want to be extra diligent, change them every 45K miles.

IamFodi

iTrader: (1)

I use Castrol GTX 5w-20 in the engine for now, mainly because that's apparently the main one used by Mazda dealerships. 5k mile oil and filter changes. Genuine Mazda filters only. Zero premix for now. Not yet sure what I'll do after the warranty is up.

In the trans and diff, I use Motorcraft fluids: XY-75W90-QLS in the diff, XT-M5-QS in the trans. Never had shift quality issues except in freezing temps. ~30k change intervals for both.

TheWyvern

Yeah, I've seen that thread a couple times. I just know that Rotarygod used RP for years from what I've gleaned, and that so long as you keep up with changing the oil every 3k it's all good.

45k is most likely what I'll do, then. Thanks for the insight.

Steve Dallas

Those gear oils are the other magic elixirs for Mazdas. Good stuff.

I used a modified version of your oil change strategy for about 3 years. I would take it to the dealer every 5K for an oil and filter change. They used Castrol GTX 5W20 in the winter and 5W30 in the summer. With a $20 coupon, doing that was cheaper (and easier!) than changing it myself with an OEM filter. After one track day, I would drain and fill with Mobil 1 0W40 and let that ride until the next dealer change. My maintenance records would show dealer oil changes with conventional oil for warranty purposes, and I would pretty much always have 30W or higher semi-synthetic in the system to make me feel better. It worked out well.

Then I discovered I could enter my own maintenance records on the MyMazda site and just started doing all oil changes myself. The dealer started requiring appointments, like some kind of silly upscale concierge service, which really turned me off to using them. They also stopped issuing coupons.

Obviously, if you are still under warranty, keeping those records one way or another is pretty much mandatory.

ZumeZume

Thanks for the advice I didn't realize pressure was the main difference in GL4 and GL5. And yes perhaps Steve and I just started off on the wrong foot in a couple of other threads water under the bridge.

ZumeZume

Haha yeah my uncle used to race dirt oval stock cars and as a teenager he coached me through my first fluid changes etc and would always tell me it's cheap insurance to change fluids all the time if you can do it yourself and instructed me to do the 2 rapid fire change on all fluids on a used vehicle. I have to admit it makes me feel better changing so often like my cholesterol drops every time I change it! lol
You raise I great point with the oil... This is my first rotary and first import for that matter. I used to be a DIE HARD AMSOIL guy but it doesn't appear to agree with the rotary. I called an AMSOIL tech he said there was a service bulletin for the rx8 and that we should be using 5w20 AMSOIL although I just decided to use conventional so the last oil I picked up was Pennzoil.

ZumeZume

Thanks... well after lots of reading I decided to go with 5w30 as a happy medium I hope. I must admit having been a synthetic oil guy for so many years it's hard getting used to conventional oil again but what are you gonna do? lol

IamFodi

iTrader: (1)

Yep. I use MyMazda as well. I also keep photos of the oil and filter containers with serial numbers/date codes in view, and log the numbers in MyMazda.

Interesting that your dealership used 5w-30 in summer. Usually, dealerships don't think critically enough about this stuff for something like that to even occur to them.

Fun tidbit: no xw-20 can be fully conventional because it would cook off too easily. So, even "conventional" xw-20 oils have at least some components in the mix that would be considered synthetic. The same is not necessarily true for a conventional 5w-30 or higher; those can be formulated with all conventional basestocks. So, in areas of the engine where high temp and high shear conditions prevail, a "conventional" 5w-20 might not actually be any thinner than a conventional 5w-30.

In my last car, I experimented with engine oils like it was my job. In this one, I'm afraid to try anything other than Castrol GTX. Rotary engines have such weird oil needs; the fuel dilution and high temps point toward a heavy oil with a tough-as-nails additive package, but the oil burning demands low deposit formation and friendliness to catalytic converters. Those are... not really opposites, but close enough. If Mazda says Castrol GTX works somehow, I'm not too tempted to second-guess them.

UnknownJinX

I have been using Pennzoil all the time. It's mostly because their interesting experiment with the synthetic oil - the Pennzoil Platinum and Pennzoil Ultra Platinum are made of natural gas. While it's not a new technology(Google "gas to liquid"), Pennzoil seems to be the only one using it on a commercial scale. The Ultra Platinum is what I am using on the V6 Accord. With the RX-8, it's funny that the previous owner has also been using the Pennzoil yellow bottle conventional, so I picked up a big jug of yellow conventional 5W-20. The oil looks pretty good, so I think I will drive 2000km and just see what happens.

I was actually reading some posts from this forum and some rotary websites regarding synthetic or conventional oil. What I gathered is that the problem with synthetic is that there is no way to predict if they burn clean, or burn at all. Conventional oil is just made from crude oil, while different brands of synthetic oil are created differently, so it's difficult to predict which ones burn well and which ones don't. It's just easier to use conventional and just change it often(5000km or 1 year, whichever comes first).

I will just stick with 5W-20 and premixing. May as well get Idemitsu Premix, which is designed to be burnt, rather than thicker 4-stroke oil that is not supposed to be burnt anyway.

That's good to know. I suppose next time I will pick up Castrol GTX.

IamFodi

iTrader: (1)

Went back with some slight edits to clarify things here and there.

On engine oils: as strongly as I feel about Castrol GTX for my own vehicle, I have to admit that the owner's manual isn't that strict. All it says the car wants is an oil with the API/ILSAC "starburst" symbol, which AFAIK just means API SM Energy Conserving and ILSAC GF-4. Plenty of good oils carry those approvals -- or better, e.g. API SN/ILSAC GF-5. So, if you chose to just pick up whatever has those approvals, I'm not gonna say you did anything wrong. I'm probably more conservative than most.



Quick caveats here.

Yes, if people can use the product for years without issue, that says something -- though I'd be careful, because "I've never had a problem" is one of the most meaningless statements in the automotive world.

Also, if your engine is breaking the oil down that badly... yeah, changing it frequently will help, but you'd still be better off with something more shear-stable. That's more in line with what Steve was saying, I think; not that RP is bad stuff by any means, but that other products are better, or just comparable and cheaper.