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#4552896 - 10/24/17 10:52 AM Those familiar w/ the RX-8 syn oil controversy...
d00df00d Online   content


Registered: 10/20/05
Posts: 11202
Loc: PA
Two common narratives that Iím sure youíve heard:

1. Some synthetics could cause deposits for some unknown reason Ė this is Mazdaís official line, and one that many independent rotary shops support
2. Many synthetics donít burn easily enough, possibly accumulating and causing problems

Iím sure youíre also aware of the plethora of synthetic engine oils specifically for rotary engines, including the one Mazda sells under its own name specifically for the RX-8. And the large number of race teams (including Mazda's own), rotary tuners, and RX-8 owners that use synthetics exclusively and successfully.

Hereís my question: Could the "synthetics cause deposits" narrative have come from cases where the oil was too combustion-resistant and too dirty for the way the car was driven? In other words, might those issues have been solved by picking an cleaner-burning oil OR by driving harder?

Royal Purple quotes a range of 500ļ F to 1700ļ F for combustion temps in this car, which seems fairly plausible. The lower end of that range isnít much higher than the flash points of some high-end synthetics. At those temps, I'd imagine those synthetics would burn, but not necessarily well, and not necessarily quickly. If they or their byproducts accumulate, they could not only burn poorly themselves, but also start to interfere with combustion of the fuel. All of that would increase deposit formation. Conventional oils might have a slightly easier time on average at those temps. Or for that matter, a semi- or full-syn with a relatively low flash point and high volatility, or really good self-cleaning, etc.

How plausible does this seem? What am I missing?
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2011 Mazda RX-8 R3
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#4552904 - 10/24/17 10:57 AM Re: Those familiar w/ the RX-8 syn oil controversy... [Re: d00df00d]
Dorian Offline


Registered: 12/07/15
Posts: 300
Loc: Ohio
I always understood it as the synthetic oil would keep the seals so clean that leaks would form and seep oil into the rotor. If a conventional was used, the seals wouldn't be AS clean and would seep less oil into the rotor? It seems like there are a few theories out there...
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#4552906 - 10/24/17 11:02 AM Re: Those familiar w/ the RX-8 syn oil controversy... [Re: d00df00d]
StevieC Offline


Registered: 08/21/08
Posts: 17116
Loc: Ontario, Canada
Who cares it's a terrible engine design anyway and those that want to keep their vehicles a good long time shouldn't buy it.
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#4552920 - 10/24/17 11:13 AM Re: Those familiar w/ the RX-8 syn oil controversy... [Re: d00df00d]
ARCOgraphite Offline


Registered: 05/17/09
Posts: 11963
Loc: N.H, U.S.A.
The new PP GTL is a paraffin so what wrong with that? Does not the engine have a preoiler tank too or does it draw from the sump?
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#4552926 - 10/24/17 11:19 AM Re: Those familiar w/ the RX-8 syn oil controversy... [Re: StevieC]
StevieC Offline


Registered: 08/21/08
Posts: 17116
Loc: Ontario, Canada
Originally Posted By: StevieC
Who cares it's a terrible engine design anyway and those that want to keep their vehicles a good long time shouldn't buy it.
No offense DF. It's just a car meant to have fun with and let it die earlier than most normal cars. IMO.
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#4552927 - 10/24/17 11:19 AM Re: Those familiar w/ the RX-8 syn oil controversy... [Re: ARCOgraphite]
d00df00d Online   content


Registered: 10/20/05
Posts: 11202
Loc: PA
Originally Posted By: ARCOgraphite
The new PP GTL is a paraffin so what wrong with that?

No idea.

Originally Posted By: ARCOgraphite
Does not the engine have a preoiler tank too or does it draw from the sump?

Draws from the sump. Some people modify them to inject 2-stroke oil instead of engine oil from the sump (only possible on 2004-2008 cars).
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#4552935 - 10/24/17 11:29 AM Re: Those familiar w/ the RX-8 syn oil controversy... [Re: StevieC]
d00df00d Online   content


Registered: 10/20/05
Posts: 11202
Loc: PA
Originally Posted By: StevieC
Originally Posted By: StevieC
Who cares it's a terrible engine design anyway and those that want to keep their vehicles a good long time shouldn't buy it.
No offense DF. It's just a car meant to have fun with and let it die earlier than most normal cars. IMO.

You're in good company. Even on RX8Club, there seems to be more desire to belittle and shut down the conversation than to keep trying to figure something out. Guess I can't blame them. This topic is old and tired, and has been fruitless for years.

Oh well. I knew what I was getting into. If I wanted to buy a car people understood, I'd probably have bought a soul-crushingly boring SUV or two. wink
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#4552953 - 10/24/17 11:39 AM Re: Those familiar w/ the RX-8 syn oil controversy... [Re: d00df00d]
CharlieJ Offline


Registered: 06/12/07
Posts: 1423
Loc: FL
Just premix 2-cycle oil at 1:100 ratio in with the gas and be done with it. Use synthetic oil. No controversy.
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#4552960 - 10/24/17 11:44 AM Re: Those familiar w/ the RX-8 syn oil controversy... [Re: d00df00d]
StevieC Offline


Registered: 08/21/08
Posts: 17116
Loc: Ontario, Canada
Originally Posted By: d00df00d
Oh well. I knew what I was getting into. If I wanted to buy a car people understood, I'd probably have bought a soul-crushingly boring SUV or two. wink


No I understand them, it's just a poor design because the seals don't wear well over the long term and the design encourages it to burn oil.

It's a great engineering feat to pull off a different complex design like this but it's just not practical. I was surprised when they revived it. I thought they learned in the 1980's.

It was a lot of wasted money for such little marketshare and for something that would never be a huge money maker. shrug

It's ok to be an enthusiast though... thumbsup


Edited by StevieC (10/24/17 11:45 AM)
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#4552971 - 10/24/17 11:54 AM Re: Those familiar w/ the RX-8 syn oil controversy... [Re: d00df00d]
HemiHawk Offline


Registered: 03/09/16
Posts: 827
Loc: PA,US
I wanted an RX8 in the worst way early 2009. But I needed a reliable daily, and something that could return decent fuel economy. Ended up with a Civic Si. Sometimes I still wish I would have experienced the RX8. The test drive sure was fun.
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#4552977 - 10/24/17 11:58 AM Re: Those familiar w/ the RX-8 syn oil controversy... [Re: d00df00d]
rooflessVW Offline


Registered: 12/24/11
Posts: 4022
Loc: North Carolina
"A redline a day keeps a new engine at bay"

If you drive your rotary in a way that benefits it i.e. get it good and hot and rev the heck out of it, I think a synthetic oil would be a fine choice.

The rotaries that die the fastest are married to automatic transmissions and get granny driven - I think a synthetic oil would be detrimental in this case.

TCW-3 in the fuel is also a good thing.
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#4552983 - 10/24/17 12:01 PM Re: Those familiar w/ the RX-8 syn oil controversy... [Re: d00df00d]
Quattro Pete Offline


Registered: 10/30/02
Posts: 35838
Loc: Great Lakes
Originally Posted By: d00df00d
If I wanted to buy a car people understood, I'd probably have bought a soul-crushingly boring SUV or two. wink

crackmeup
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#4553007 - 10/24/17 12:17 PM Re: Those familiar w/ the RX-8 syn oil controversy... [Re: rooflessVW]
d00df00d Online   content


Registered: 10/20/05
Posts: 11202
Loc: PA
Originally Posted By: rooflessVW
The rotaries that die the fastest are married to automatic transmissions and get granny driven - I think a synthetic oil would be detrimental in this case.

Why is that?
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2011 Mazda RX-8 R3
Mobil Super 5w-20

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#4553024 - 10/24/17 12:39 PM Re: Those familiar w/ the RX-8 syn oil controversy... [Re: d00df00d]
rooflessVW Offline


Registered: 12/24/11
Posts: 4022
Loc: North Carolina
Originally Posted By: d00df00d
Originally Posted By: rooflessVW
The rotaries that die the fastest are married to automatic transmissions and get granny driven - I think a synthetic oil would be detrimental in this case.

Why is that?

Just a feeling, nothing scientific.

I would think that a synthetic would leave more deposits in a mildly driven rotary? It's resistance to burning would leave a gummy residue that could build up on apex seals.

Driving it at full tilt would burn/blow that out.

I would think. I don't really know.
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#4553041 - 10/24/17 01:00 PM Re: Those familiar w/ the RX-8 syn oil controversy... [Re: d00df00d]
mazdamonky Offline


Registered: 12/08/15
Posts: 556
Loc: Arkansas
Being a Rotary engine guy, Synthetics by american standard are not an issue. Current day synthetics in general shouldn't be an issue. But the oil that is provided by Mazda Japan for the rotary engines is a Group III oil which by their definition is not a synthetic. Here in the US, Group III oils are synthetic and almost all of our over the counter Synthetic oils are Group III. I personally would recommend using an xw30 or xw40 weight oil. In my RX7, I generally use 0w40 Castrol or 15w50 Mobil. It seems to really like both.

Sadly the real problem with oil in the Rx8 is the original spec is too thin. Tolerances are the exact same as older motors where xw40/xw50 oils were prescribed. It is also recommended to add 2 stroke to your gas. This helps keep the inside of the motor properly lubricated in the event there are issues with your OMP.
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