ventyboi

Hey guys I recently got a 2004 Rx-8 and it had full synthetic in it already so I went ahead and stuck with that for the first oil change. Ik it’s not preferential but also didn’t know what else I could do since it’s not really easy to completely change the oil and I’m pretty sure mixing full synthetic with conventional oil is bad. Anyways it’s time for another oil change and the place I got oil from said I could put marvel mystery oil in the oil run it for about 30 minutes then be able to change over to conventional motor oil with no problems is this true?

NotAPreppie

Don't put anything other than motor oil in the engine.

Synthetic, dino doesn't matter as long as it meets the minimum requirements listed.

There's nothing wrong with mixing types if you want to switch to dino but there's also nothing wrong with sticking to synthetic.

The average drain/fill gets about half of the total oil out. If you're set on switching to dino and you want to get all of the old oil out, you'll have to do multiple changes in quick succession. After the first change, it will still be 50% synth. Let it idle for 30 minutes and it change it again and you'll be down to 25% synth. Do this again and you'll be down to 12.5% synth and so on.

ventyboi

So I can just change the oil like normal and put in conventional oil with no problem mixing it with synthetic?

dannobre

iTrader: (3)

You can mix synthetic and conventional oil all you want. There is nothing that will happen if you mix them. What do you think semi-synthetic oil is?

Personally I wouldn't use MMO for anything

Just use a 5-30 and don't worry about it. Change it often and change the filter with a good OEM or similar.

NotAPreppie

I updated my initial reply but yes.

In theory, there could be some odd chemistry that might cause a problem but in practice, it's incredibly unlikely (I'm a chemist). Any time oil manufacturers tell you not to do this, they are just covering their asses in case something bad happens.

See above about how to get all of the synthetic out.

Or you know, just stick to synth.

ventyboi

Alright cool thanks a lot guys! Sorry if that was a dumb question I just want to make sure I don’t mess up and I got an k&n oil filter

ventyboi

I was worried about the synthetic cause I’d read elsewhere and watched YouTube videos saying it wasn’t good for the engine

furansu

Argument against synthetic:
-Mazda's official recommendation to owners is conventional motor oil, with very few exceptions -- the only officially endorsed one being Mazda's Japanese-only Synthe-Renesis Engine Oil)



Argument for synthetic:
-In Japan Mazda and Knightsport have both offered synthetic oils that are rotary specific.

-Mazda's racing teams indicated that they use synthetic oil in their race cars, but could not comment on the quality of all synthetic oils publicly available.

-RacingBeat suggests and uses synthetic in all of their rotary-powered cars.

-Royal Purple has tested the formulations of their synthetic oils to be compatible with the soft seals inside a rotary engine, which was one concern of note from years past -- no other oil supplier has publicly stated such testing for their products, though that doesn't mean with certainty that they are indeed incompatible.

-I ran synthetic in my FD for many years, with no ill effects. The inside of the engine was no worse than any other rotary I've taken apart, with no notable build up in any area (reason for disassembly was a broken apex seal from an overboost condition at 72k miles). I currently run synthetic in my RX-8, including a semi-synthetic 2-stroke oil for oil injection via the SOHN kit and pre-mix via the fuel tank.

My inputs above look imbalanced, but it could be argued Mazda's official stance bears far more weight. I lean on the experiences of those that have been using these cars in high-load conditions for many years, my own anecdotal experiences, and the supposition that Mazda may just be covering all basis and playing it safe since they didn't have resources to spend testing all available oil formulations in long-term road condition use.

Draw your own conclusions and use what you are most comfortable with in your car, but synthetic is fine in my book.

40th8Jake

Royal purple 10w-40 baby


And the oil is purple.
But amazon basics probably works too.
how deep ya pockets and love for rotary

Loki

iTrader: (1)

Keep in mind that Mazda's original recommendation, and recommendations of rotary specialists, are largely rooted in oil made in the 90s. Oil formulations have changed several times since then as evidenced by API spec revisions. It's also important to note that 'synthetic' is not a good description of oil. There are different base stocks and groups of oil.

I've been running synth since 2011 including RP at one time, but have settled on LiquiMoly synthoil based on excellent used oil analyses from my own car for years, even at 5000 mile change intervals.

wannawankel

I have been buying and using WalMart Supertech 5W30 (SAE SN rated) with 1000-3000 mi OCIs in addition to adding (JASO FD-rated) 2-stroke oil to my gas tank at a usage of 70-100 mL per tank.

delhi

Castrol GTX 5w30. My OCI is around 5000km or less. No need for synth.

CaymanRotary

I run Castrol GTX 10W40 conventional in all my 8's. All are still very happy. Synthetic not worth it due to frequent oil changes. Only good if you have a SOHN adapter.

scruggyj

No need to spend money on expensive oil that will get changed frequently.

40th8Jake

I use Royal purple just because I do not daily mine. I daily a Camry. I live in SoCal and visit the Racing Beat showroom when I purchase stuff and chat with the guys in there. If it’s good enough for them I’ll use it. Racing Beat independently tested various synthetic oils and RP came out on top. Next upgrade for me is SOHN adapter to get full use of synthetic oil. If I did daily mine I would use Castrol 10w-40 conventional.

Steve Dallas

There is no evidence it matters what you use, if you drain and fill every 3K miles and change the filter every 6K miles. Use whatever makes you happy.

HoldMyWankel

From what I’ve read up on, I wouldn’t use anything but full synthetic. Rotaries are notorious for burning oil; it’s almost part of their identity. Dino oil doesn’t burn clean so it will leave more carbon buildup in your engine which can lead to seal problems and compression issues. I use royal purple but Mobil 1 has also had very good reviews in the rx8. Hopefully I was helpful!

Steve Dallas

They are not "notorious" for burning oil; they burn oil by design. It is all dirty crankcase oil that is not designed to be burned; it all burns dirty. Use synthetic because of its shear resistance, not because of any burning properties.

.

DannyR3

1. They're designed to burn oil, not notorious for it.
1a. It's not "almost" part of their identity, it IS part of their identity, and design.
2. You want to use regular oil, not synthetic.

40th8Jake

The debate that will never be settled.
Just make sure you have oil at least and that it’s at least a 5w-30 or heavier. Someone will probably contradict even this and say to use the factory 5w-20 (don’t do it).

Steve Dallas

The oil wars are over, and the outcome is known.

It almost doesn't matter what you use; just perform a drain and fill every 3K miles (filter every 6K).

These engines have several failure modes and failures appear to be more or less random. The only failure mode that can sometimes be directly attributed to oil is bearing failure, and we never have the service history of those. Otherwise we have seen engines fail anywhere from 1K miles to 200K miles, and it cannot be proven that a different oil would have saved any of them. The engine is going to do what it is going to do.

(My own engine [that saw the track every few months] developed a small coolant seal failure at ~30K miles and failed compression at 45K miles. I used Mobil 1 0W40 and premixed and took all the other precautions. None of it mattered. It died because of its specific assembly, and there is nothing I could have done about that.)

In my 8 years of reading this forum, I have never seen convincing evidence that any particular oil is better or worse outside of extreme conditions (track cars, etc.) when changed frequently.

Again, use whatever makes you happy and change it frequently. Premix if you have an S1 or just want to. Then roll your dice.

.

Loki

iTrader: (1)

The bearing failure seems to correlate with a lot of short city driving leading to fuel in the oil. I don't have first hand research on this obviously but it has been reported by rotaryrevs and other shops. It would make sense.

That said, like any incident, there are usually multiple factors so choose the oil based on duty requirements (are you racing and need more than usual heat tolerance and protective qualities?), and change as advised above oe run your own used oil analyses and extend if it looks safe.

CaymanRotary

Well, within reason I suppose. Definitely use thicker oil if you are in a tropical environment or are tracking
Dont use 0w20 though because it's much too thin. I've been happy with 10W40, works perfectly and is inexpensive. You are wasting your money if you run synthetic in my opinion anyways. The secret is oil changes every 3000 miles as you said and you should have a happy engine.