I've had my RX-8 since it was new in 2005. It has only 24,000 miles on it, but I started looking at the maintenance schedule and realized that after 20+ years I'm probably a bit overdue to change my coolant, trans fluid, brake fluid and diff oil. Any suggestions based on experience for any of these would be appreciated. The one place I'm unsure about as far as fluid choice is the diff. The trans calls for 75W90, while the diff is spec'd out for 90. I bought some Mobil 1 75W90 which I am sure will be fine for the trans, but now that I look at the manual I'm wondering if ti will be OK for the diff.

 

That Mobil 1 is a GL5 oil, do not use it in the trans. It will eat the brass in your synchros over time. GL4 only in the trans. RedLine MT90 and/or MTL are a common go-to here.
In the diff, you do want GL5. RedLine 75w90 NS for example. Keep in mind it's an LSD, you want an oil specified for limited slip.
You could also go with Mazda's stuff. It works just fine.

And definitely only Mazda FL22 coolant.

 

Weird, the forum swallowed my reply. Here it is again.

That Mobil 1 is a GL5 oil, do not use it in the trans. It will eat the brass in your synchros over time. GL4 only in the trans. RedLine MT90 and/or MTL are a common go-to here.In the diff, you do want GL5. RedLine 75w90 NS for example. Keep in mind it's an LSD, you want an oil specified for limited slip.You could also go with Mazda's stuff. It works just fine. And definitely only Mazda FL22 coolant.

 

OK, well so much for your opinion. This is right from the Mazda Owner's Manual. Manual transmission oil - specifically states a GL-4 OR GL-5. I don't think they would spec that if it ate up the brass parts in the tranny. Differential is stated as GL-5, but only shows a SAE 90, so I was concerned about using a multiweight oil. I've attached a copy of the page from the manual.

 

Ignore what you read in the manual VT, like Loki said do NOT use a GL-5 oil for the transmission. Use GL-4 in the transmission. Go with the Redline MT-90.

 

Cool, do a search on this forum for "GL5 synchro grinding" . Lots of history since the manual was written.
Oils have changed and lomg -term issues have manifested since the manual was written.

 

Also the NC Miata 6 speed is the same AZ6 as the 2004-08 RX8 and that manual calls for GL4. Maybe they learned something :o

 

Plus 3 on not using the GL5 on the transmission. Mazda owners manual also recommends you use 5w-20/ 5w-30 on the engine oil and every Mazda expert will tell you otherwise. I am running the Mobil 1 gl5 on my differential and it works good. I would recommend keeping it and using it on the differential. For the Transmission - Redline MT90 is highly regarded and even most recently - some people recommend Redline MT-LV which I am currently using and am very happy with (both are GL-4).

 

Loki, I owe you an apology. After rereading your post. I did a bit of research on my own and now feel like I understand the concerns. Good thing I posted to this forum. I just ordered a couple of bottles of Red Line today for the tranny and I'll use the Mobil 1 in the diff.

I would like to know why you say not to use anything but the Mazda coolant. It seems like the Prestone Platinum is a good product. It's a 15+ years and 350,000 mile product, which makes me feel like maybe it will last a few years and has the additives and stuff to protect the aluminum and other parts.

What are you thoughts on the brake fluid? I have a bottle of DOT3/DOT4 Valvoline synthetic. I haven't seen anything about cautions on using it in the 8 and also don't know what the difference is. I have to say that I have always been cautious about multi use products. If it is good for both DOT3 and DOT4 I have to wonder if it is ideal for either, or just OK.

 

The only concern I have about using the MT-LV is that it is a lighter weight oil, 70W75. Not that I race or anything. I rarely go more than 100 miles or so. However, I am curious if it has any benefits over the 75W90 that is specified, like smoother shifting, that kind of thing.

As far as motor oil, the only thing my manual specifies is 5W20. There is no other option mentioned. I also note that despite the belief that you should never run a synthetic in the rotary, there is nothing in the manual to that effect. They simply state the viscosity and ILSAC certification. I am currently running Castrol 5W20, which is a synthetic blend. I would far prefer to run a full synthetic in a higher viscosity if that is safe to do. I always thought the engine should have a separate reservoir for the injection oil rather than drawing dirty oil form the sump. When my car was new there was a (supposedly) bolt on aftermarket system that did just that. I have heard of people running 2 stroke injection oil, since it burns compleltey and has exceptional lubrication properties and is designed for injection systems. Clearly not suited for the sump in a pressurized system where additives to absorb acids and moisture are essential.

 

Keep in mind, the manual is 20 years old. Oil has changed since it was written, I'm not even sure you can buy API SM certified oils that were standard in 2000's any more, we're up to SP and the compositions are driven by the needs of hybrids and emissions equipment. The 5w20 recommendations is also only in North America, speculatively for CAFE reasons. Elsewhere Mazda recommends 5w30 and apparently even has OEM synthetics for rotaries. I have run synthetic 10w40 since 2012 and haven't had a problem, but you can make your own decisions on that. Not all synthetics are the same stock, so the choice of specific oil matters. If you don't want a degree in oil chemistry, you can stick to regular oil but with higher viscosity.

About the coolant: Mazda's soft seals are susceptible to 2EHA, which is a common ingredient in off the shelf coolants. It won't kill you overnight, but there's nothing to be gained by using another coolant anyway. Definitely never use Water Wetter or other junk in there.

The 2 stroke oil idea requires a Sohn adapter, you don't run it in the sump. I have this set up, no complaints. Helps keep the expensive synthetic oil out of the combustion chamber. Make sure to you proper 2 stroke if you go this route, they're not all the same. You can premix 2 stroke oil in the gas, which is easier ot manage. A clean burning JASO FD 2 stroke won't hurt anything, and premixing delivers oil to where the oil injectors can't. If it's actually extends the life of your engine - not enough empirical data, but it's cheap and common enough to go on faith.

 

What brand of synthetic 10W40 do you run? No point in reinventing the wheel if you've had good results.

 

LiquiMoly. But, keep in mind, it doesn't get injected, because of the Sohn adapter.
There's another thing to look for, which is ZDDP content. BradPenn oil is gear toward racing but a number of shops swear by it. The theory is ZDDP makes oil cling to surfaces better so your cold starts are always lubricated, leading to less wear. Can't argue with it, don't have empirical data either way. But I may switch to it. Again, the Sohn adapter matters because you don't want Zinc in you catalytic converter from burned injected oil. The LiquiMoly choice was based on racing needs at the time, I no longer do that. Car is at 150k km, original engine.

 

I.m learning all kinds of things I didn't want to know, but need to. It's tragic that a common ingredient in modern day coolants attacks silicone, when that is the most common seal material in modern cooling systems. I certainly don't want to take a chance on that. I am wondering if there is something more in the way of a cleaning agent, etc that I should be using, given the fact that the coolant has never been changed and the car is 21 years old.

Alos, do you have nay concerns about using a DOT3/DOT4 synthetic brake fluid, specifically Valvoline.

 

I'll chime in about brake fluid. I use Motul 600 fluid, quality DOT approved stainless braided lines on the entire system (brake and clutch). I'm happy with the results. I also put speed bleeders on the entire system to make my life easier.

That said if you ever need to replace a clutch master or slave, I strongly recommend replacing both at the same time and bench bleed both of them. It will save you a lot of time and spare you a lot of stress and frustration.

 

If the coolant is 20 years old (yikes), it eventually turns acidic, so I would do a distilled water flush or two after draining what's in there. Then put fresh coolant, which hopefully neutralizes any remaining acid.

Brake fluid is mostly brake fluid if you're not racing. Valvoline sounds fine to me.



...

 

When you say a distilled water fluch or two, are you saying to refill with distilled water and then run the engine to normal operating temp, then flush, or just flush, letting it run out the drain plug? There are a lot of coolant system flush/cleaners out there, but since it is impossible to drain all the fluid (there will always be some in nooks and crannies that doesn't drain out) I would be concnered about traces of it left behind. Neutralizing the acid sounds like a good thing to do.

 

Fill with distilled water, run up to operating, then drain. I hadn't considered flush additives, now that you mention it, and I don't know too much about them. Others might.

 

Here's the thread I ran across after using MT-90 on all my cars prior. It's not for everyone but in my experience it works for me. I usually don't abuse the tranny and noticed that the shifting is always smooth regardless of the weather being cold or hot. I did notice that at high rpm shifting it goes into gear easily. I am in the California bay area so never experience weather extremes of each. Here is link:
https://www.rx8club.com/series-i-tec...-fluid-270351/

 

You can use other coolant brands - I think the main thing is to stick with the green stuff and not use the universal coolants that are other colors as the contents can cause corrosion over time. I have good experience using Peak that states it specifically is formulated for imports that includes Mazda. Since it's been so long since you changed the coolant. I would recommend you get a concentrated coolant container and flush out the coolant as much you can with pure distilled water. You will be able to see contamination of the coolant easily with the clear water and once you see that the water doesn't contain debris you can proceed with making your coolant mix (70/30, 80/20, 60/40 etc.) I personally run 80/20 water to coolant as I also add a bottle of Redline Water Wetter, RP purple Ice, or VP Water Cooler depending what's available at the part store.

 

Don't use water wetter with any coolant in the system, even says not to on the wetter bottle. It can cause gumming up and obstruct passages too including inside the radiator and overall negatively impact performance. Just dilute the oem coolant with distilled water to your liking

 

Lots of good info. Thanks, everyone. Here's my plan. Please comment if you think I'm making a bad decision on any of this, or if you disagree with what I'm saying.

Before I read the post on choosing tranny oil, I had already purchased the Redline MT90, so I think I'll go ahead and use it, since I haven't heard a lot of complaints about it, except from the link provided by Topgun.

https://www.rx8club.com/series-i-tec...-fluid-270351/

After reviewing that in detail, I have to wonder if some of the trannys he tore down had already been filled with a GL-5 and that's where the wear came from. Many people buying cars back in 2005 would take their car to "their mechanic" who they trusted, rather than the dealership, especially by the time it would require a tranny fluid change. He would likely have simply used whatever he had on hand. Anyway, I didn't see anything conclusive there that would prevent me from using the MT-90 and there were a few responses to this thread that spoke favorably of it, so I may as well give it try. If I detect any kind of reduction in performance I'll likely swtich to the MT-LV. Keep in mind, this car has only 20K on it and the fluid has never been changed. I'm not changing the oil for any issue other than its age. The transmission has always shifted smoothly.

I have not found a Mazda FL22 fluid that is concentrated. I have never used premix except as an emergency after coolant loss. Using the concentrate and the cooling system capacity stated in the manual is the only way to get an accurate mix when flushing and refilling since you really don't know how much water stays in there. Anyway, I found this at Oreilly locally so unless I hear bad stuff from somenone, this is what I will use.

https://www.oreillyauto.com/detail/c...hicle+specific

It sounds like no one endorses a flushing agent or additive. I have to agree, since you never know what kind of damage the flushing agent could do.. I'll drain the fluid and see what it looks like. Given the age, it's likely to be ugly. Since the coolant is the only lubrication the water pump sees, I really don't like the idea of running without it, but I see no other way to flush all of the old fluid out because I'm guessing you need to run it up until the thermostat opens in order to get it circulating. I plan to flush and fill with distilled water multiple times until the water is clear, then put in the amount of coolant needed and top up with distilled water.

I'm going to go ahead and use the Valvoline brake fluid I have. Does anyone have any words of wisdom regarding the bleed process? I like to remove as much fluid from the reservoir as possible before adding new, just to keep from diluting the new with the old, since it takes longer to bleed it clean. However, I have heard of issues with the baffle in the top of the reservoir causign issues and after looking at it, I really have no idea how to get the majority of it out.

The rear diff will get the Mobil 1.

I plan to change the motor oil as well, but this is an interesting one. I have run Castrol GTX 5W20 since the car was new. The oil has never gone more than 3K miles, and generally much less. I lived in VT and only drove it during the summer. Since moving to FL, it only sees limited use, so oil changes have been at a far lower mileage, based on age. GTX is now only available as a blend in the 5W20, even though it is classified as a "conventional" motor oil. I've used that in my last change and have another bottle, so I'll use that again this time. It is available as a true conventional oil in a 5W30, so I may switch to that. The thicker oil will definitely not be a problem in FL. With the low useage I would have a difficult time using a more expensive oil.

 

Sounds good. The Zerex coolant says no 2-EHA so should be safe. That said though, premixed FL22 is what the Mazda dealer would use and while some water might remain, if you drain the block correctly, it not likely to change the coolant watter ratio much. 5w30 sounds fine. You could even go to 40 given that it's Florida.

Check/replace your rad cap while you're in there. If it's 20 years old, that's cheap insurance.

For later in your projects: the plastic coolant overflow reservoir becomes a liability with age and hot climates. Don't touch it unless you're ready to replace the rad, the plastic end tank nipple will fall apart if you try to change the reservoir. If you are missing the plastic engine under tray for any reason, you'll want it back on by Florida summer, it's a key part of radiator function.

 

What's your opinion of running the car up to temp with only water? I'm wondering if it's worth what might be gained versus teh Mazda recommendation, which is flushing with plain water with the drain open until it runs clear. I don't know anythinbg about the path the coolant takes, but I have a hard time believing that it runs through and rinses the entire block. I wonder if it would make sense to fill with an antifreeze mix and run it a while, then drain and rinse before a final fill. Low mileage, but 20 years is likely to have caused a bit of corrosion or gunk.