I didn't see this anywhere else so I apologize if this has been posted already. Royal Purple added a section to their FAQ page that deals specifically with the rotary engine. I'll just copy and paste it below.



"Rotary Engines

Can Royal Purple Motor Oil be used in a rotary engine?

Yes. A rotary engine is a modified four cycle engine that recommends the use of an API licensed motor oil for street applications.

More information and FAQs on lubrication of Rotary Engines:

In a rotary engine, the oil lubricates the eccentric shaft bearings, thrust needle bearings and rotor bearings similar to a crank and rod bearing of a piston engine as well as being injected into the combustion chambers to lubricate the apex seals, corner seals, and side seals helping to create the sealing mechanism doing the equivalent job of the piston rings.

Royal Purple provides outstanding protection for the e-shaft, rotor bearings, thrust bearings and is suitable for the oil injection system as it has proven to run cleaner than other oils and is an excellent choice for rotary apex seals, corner seals, and side seals.

Mazda makes a statement in the Owner’s Manual not to use synthetic oils in a rotary engine, why do you say that it is OK?

Royal Purple has performed seal compatibility testing on the components used in a rotary with excellent results, including older rotary engine seals dating back to the Cosmo. Royal Purple’s Technical Services Manager David Canitz has been an owner and racer of rotary engine cars and has used synthetic motor oils in rotaries since 1985 with excellent results. He has been trying to find an answer to this Mazda statement for the last 18 years.

In the early development of synthetic oils decades ago, there were purportedly some seal compatibility issues. Today’s synthetic oils do not have the compatibility issues of the old oils. There is no substantiated evidence of seal compatibility issues with Royal Purple.

Here are some facts:

The Mazda Factory racing departments recommend and use ‘synthetic’ oils including the winning 1991 Leman’s 26B 4 rotor Mazda 787B.

MazdaComp USA printed manual (now Mazdaspeed) recommends the use of synthetic oils for racing conditions.

Royal Purple Motor Oils have been used in rotary engines (both race and street) for ten plus years with excellent results.

Royal Purple Motor Oil is compatible with the bearing material, sealing elastomers, and combustion seals used in a rotary engine.


I heard that synthetic oil doesn't burn like mineral based oils and will coat the inside of the engine with deposits.

If this was a problem with synthetic motor oils in general, then all internal combustion engines using a ‘synthetic’ would experience increased deposits on internal surfaces. The opposite is actually the norm.

Conventional four cycle motor oils will typically leave deposits of carbon and ash when injected into the rotary apex seal, corner seal, and side seal areas. Royal Purple’s motor oil actually burns cleaner due to the synthetic base stock being free of contamination and many of the additives being ‘ashless’. This may not be true for all synthetics but Royal Purple has been proven to work extremely well in rotary engines.

Royal Purple’s formulation of synthetic hydrocarbon motor oil does burn at the nominal combustion temperatures experienced in both street and racing applications, whether normally aspirated, turbocharged, or supercharged. (500 – 1700° F idle to race rpms typical combustion temps)

Will the synthetic oil effect the oil seals?

No. Royal Purple’s Motor Oil is fully compatible with the elastomers found in rotary engines as well as more conventional piston engines. The oil seals, housing seals and other elastomers used in rotary engines typically consist of Buna N, Nitriles, Neoprene, or Viton materials which are also commonly found in piston engine cars.

I hear that synthetic is ‘thinner or lighter’ oil, is there a greater possibility that the oil will leak between the seals?

No. If an engine’s sealing surfaces are in good condition, synthetic oil should not cause any leakage. However, if an engine has marginal seals, there is a 50/50 chance the seals will leak less or more. A synthetic motor oil is going to have similar viscosity to that of a conventional motor oil – except at extreme temperatures. Due to a flatter viscosity curve, at low temperatures it will not thicken as much (easier winter cranking) and it does not thin out as quickly at higher operating temperatures (better oil film at higher rpm).

Should I go longer or shorter between oil changes?

Royal Purple recommends that the maximum oil drain / filter change interval listed in the Owner’s Manual be followed while under warranty (new RX8). For SA, FB, FC, FC Turbos, and FD rotaries, extending drain intervals from two to five fold is possible if desired. Since the rotary engine injects oil through the use of a metered oil pump, either adding oil into the carb base plate air / fuel mixture or directly injecting oil into the rotor housing, rotary engines will consume oil of one quart per 1000 – 3000 miles. It is important to maintain the proper crankcase oil level in your rotary engine if you decide to extend oil drain intervals.

If I pre-mix my fuel for the rotary engine, do I use the same ratio as with mineral based oils? Does it burn at the same rate?

In an ideal world, the rotary engine metered oil pump should inject an ashless oil designed to burn in the combustion chamber and use a four cycle oil in the crankcase for the eccentric shaft, rotor bearings, and thrust bearings. For the street, Mazda simplified the OE system to use just one oil, that being a typical four cycle oil for both the e-shaft as well as the combustion chamber. Royal Purple recommends using our standard TCW III 2 Cycle Oil if the metered oil pump is still enabled. The two cycle oil being added to the fuel tank is in addition to what Mazda designed to inject and acts as a supplement or insurance. Depending on which engine, the level of modifications (street port, Bridgeport, peripheral port, nitrous, turbocharged) and application, the typical mix ratio could vary from 200:1 to 800:1.

For a pure racing application where the metered oil pump has been disabled or removed, again based on the actual engine and modification level, the ratio could vary from 150:1 to 600:1. For this application, we recommend our Racing 2 Cycle TCW III product or the standard 2 Cycle TCW III can also be used.

A stock FD twin turbo 13B with the MOP oil injection system can typically use about one quart per 1500 miles under hard street driving. If this vehicle is getting 15 mpg, the gasoline to oil ratio is 400:1. If the oil consumption on this vehicle reduces to 1 quart per 2500 miles and fuel efficiency increases to 20 mpg, the gasoline to oil ratio increases to 600:1. The stock metering oil pump is a great system as it varies with throttle position (load on the engine). Pre-mixing has to be calculated for the ‘worst case’ that will be seen by the engine for that fuel load. Under racing conditions, that’s wide open throttle at racing rpms. This means that at idle, the ratio may be slightly fat (rich)."




I think that about sums it up nicely! Thanks Royal Purple!

RG

I've even using it for a many years now. Even Racing Beat recommends Royal Purple although before they did, they used Amsoil.

Everyone should understand that I don't say that you should not use conventional oils. I'm just against people saying that you shouldn't use synthetics. That's a rumor that needs to go away. One reason why I use RP is because they obviously know a thing or 2 about rotaries. It's obvious by looking at their FAQ page. They obviously understand what goes on in a rotary and have actually gone to the trouble to test in them.

I do have to laugh at the people who claim that Idemitsu is somehow specialy formulated for the rotary when other synthetics aren't. I have to ask, what makes it so special? We all know that what makes a motor oil a motor oil is the additive package. The base stock couldn't cut it on it's own. All oils use basically the same types of additives just in different proportions. It definitely can't be them that is special. What about the base stock? Could that be it? What makes a synthetic a synthetic is the base stock oil. Idemitsu is a group IV PAO. So is RP and several others. That can't be it. So what is it that makes it so special and safe for rotaries? I'll let you in on the big secret. Shhhhh...... Mazda endorses it because one of their guys had a hand in formulating it with Idemitsu. That's the secret. There's nothing special about it other than that. Last I checked it's what it's made out of that counts, not who did the mixing.

There is one thing that stands out about Idemitsu. I've seen an oil analysis of it which is why I crack up at the claims hat it is good and others aren't. It contains unusually high levels of molybdenum. Many other oils contain this as well. Just not in as high a quantity. Does this make it rotary compatible? Nope. As I said other oils have it as well so that can't be it. Why the large amount? They developed this oil for racing and not street use. For racing they wanted extra lubricating ability. Makes sense, it's for a race car. Molybdenum however will settle out over time. What will happen if you use this in a street car that doesn't get oil changes as often? Where do you think this molybdenum will go? Does that sound like something you want in your street engine just because it is "rotary formulated"? That's an oil I'd save for the track.

The whole point is that nothing makes a synthetic bad for a rotaries and conventionals good. This is the 21st century. 30 years ago there may have been issues. Use whatever oil you want. That's fine. Let's just stop continuing to spread false rumors that synthetics are bad. They aren't and evidence strongly suggests they are better.