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Hello everyone. It's been a long time since I have made a post here. It is well known that every stock RX-8 draws oil from the sump to provide injected lubrication to the rotors. Because of this and the need for the oil to burn off, synthetic oil is not an option. Even synthetic 2-stroke oil which would be a great option for injection is not appropriate, since it does not contain the detergents and other additives necessary to live in the crankcase. I suspect all of you have experienced the issues with availability of conventional oils. Most manufacturers have moved to synthetic blends as their entry level oil and no longer offer a straight conventional oil. I have been using Castrol GTX from day one and it is still available from Auto Zone and probably other places, but the field continues to narrow and the day may come where a 5W20 conventional oil is no longer available. Has anyone heard of a blend or other option which can be used successfully without contaminating the cat converter or cause other problems? Because every motor oil formulation is proprietary, I have always made it a policy to stick with the same brand to prevent compatibility issues, so I have been unwilling to try other alternatives. I see a day coming when I will have no other choice. I'd like to explore what options may be available before that day comes.
I change my 5W30 conventional often - between 1000-3000 miles and use Walmart Supertech SAE SN+ rated oil made by Warren. When my engine was under wanrranty - I used the superest Supertech 5W20. My theory - and it's just a theory - that change oil more often is better than a Brand name oil changed less often. I change the oil filter every other OCI.
I've used SuperTech conventional in my other cars - namely the 1992 Integra GS-R that I had over 250000 miles - only selling her when I needed a SUV a few year back. My CRV had 150000 miles on SuperTech 5W20/30 mix.
SuperTech is SN and now SN+ rated and meets all the SAE requirements.
Synthetic is fine, Mazda's own oil is a synthetic blend. What you are referring to may have been true in early 2000s when the RX8 manuals were written, but oil certifications have evolved as much as cars have since then.
"Synthetic" is a meaningless label, if you would like to understand oil chemistry further, look into oil groups and choose from there. The additive formulations may be proprietary but there are relatively few possible base stocks.
You can also get an adapter that lets you run separate crank and injection oil. Synthetic in the crank, 2 stroke for injection, best of both worlds.
There are numerous threads on this, please search. Of particular interest may be the used oil analysis thread.
For the specific question, check if the regular and synth versions of your preferred oil have the same API cettifications. I suspect they do, and it is SN or better, which means their lubrication properties, breakdown (which leads to deposit forming) and heavy metal content (for your cat) have been tested to the same spec. Which means you can use them interchangeably for most usecases.
I just wanted to add that in my 8 I also use the Walmart brand (SuperTech) conventional (10w40) and change it every 2k mi., filter every other change. This method has worked out well for me.
OK, sorry I haven't chimed in, but your responses were spammed and I don't check the forum that often. I moved from VT to FL recently and it's been a challenge. I'll try to answer all of the replies, but if I miss something, please respond. I think this is an important thread, at least for me.
Loki, you mention oil formulation, bases, spec numbers, etc, but it seems to me matching the flash point is very important and historically conventional oils will burn off at a much lower temperature than synthetics. As I recall, the combustion temperatures in the rotary engine are far lower than conventional piston engines because of the shape of the combustion chamber - there's a lot of surface area. I doubt there is a crankcase oil out there that has been tested for injection into a combustion environment, conventional or synthetic. From what I recall, these tests typically look at wear, deposits, and an analysis of used oil after it is subjected to certain operating conditions, but all relative to the crankcase. I don't think any of them would address what happens when you inject it, it is intentionally burned and then passes through the cat. I can tell you that at least Castrol is unwilling to endorse its use in that way and Mazda certainly does not endorse a synthetic. I guess I'll have to take some time to research this, which kinds of defeats the purpose of starting this thread, I had hoped someone would already have done that.
I definitely agree that an injection system with it's own reservoir is the perfect world and Mazda should have designed it that way to begin with. People put gas in their cars, if they know they need to keep injection oil in a separate tank full as well, I think most folks could have handled that. They tried way too hard to make a unique powerplant feel the same to consumers as a conventional piston engine at the expense of longevity.
I have changed the oil way more often than required, since I did follow the standard of changing the oil and filter before putting it into storage every winter. It's never seen a year of more than around 3K mi. I bought it in 2006 brand new from a dealer, so that is 14 oil changes in 20,000 mi. My thought was that the oil and filter were cheap compared to a rebuild and fresh oil in the crank means fresh oil to the rotors, where it really counts. At the time the external injection kits were expensive and labor intensive and I simply hadn't the time or money to put into it, so frequent oil changes were the compromise. I'd love to retro my 8 with that and use full synthetic in the crankcase, just the way any purist engineer would have designed it. Unfortunately, I can't seem to find one any more. If someone knows of a retro, I'd love a link.
I appreciate the feedback on other brands of oil and that's what I plan to do for now, but I am looking ahead to when conventional oils are abandoned altogether. I don't think that day will be very long in coming.
Incidentally, I am very **** about this car which plays into my concerns. The longer I own it, the worse it gets. This is a 100% stock original, showroom condition 2005 base 6 speed with just over 20,000 miles and I am the original owner. Stored winters, rarely driven in the rain and has spent most of its time under a cover. It still smells new when you get into it.
Mazda offered synthetic for RX8s outside the US. And this was 16 years ago. The behavior of oils when burned is far more complex than just synthetic vs non-synthetic. Most 2-stroke recommended for rotaries is synthetic or synth blend specifically because its burn qualities can be controlled. Not the same stock as basic consumer synthetic engine oils, closer to what higher end synthetics are made of
You're welcome to use whatever you feel is best, just make sure you're doing it for the right reasons.
The oil adapters are called Sohn adapters, and a member here called Epitroch sells complete kits with reservoir and all for $180 I think. Great kit.
The adapter itself comes from RotaryAviation.com, about $100.
The problem I have with commercial 4 stroke synthetics is they are not blended for injection. Synthetic 2 stroke oils are specifically blended to be low ash, low residue and for injection and are probably far better than any conventional oil. I raced 2 stroke snowmobiles for 10 years and I know what the chambers/ports looked like with a conventional vs synthetic 2-stroke oil. I used the best oils out there and even with those, the synthetics still had far more residue. Despite that, I used the synthetics because the wear properties were so awesome. Engine wear differences between synthetic and conventional were remarkable. The exhaust valves and chambers needed to be cleaned more often, but rebuilds were able to be pushed out and performance was slightly better as well. No cat to plug up, so it was an easy choice. My point is, even synthetics designed to burn in a 2-stroke environment were more prone to deposits than the conventional oils. Synthetics designed for use in 4-stroke engines are actually blended to resist burning except at very high temperatures, which is one reason they are so good in extreme use environments. As I mentioned before, the rotary combustion temps are lower than 4 stroke, so that exacerbates the problem. Unless I can go to a direct inject system rather than drawing from the sump, I'll stick with conventional. I'll look into the kit though, thanks for the info. Given my all stock immaculate vehicle, unless this is reversible - no permanent changes to the system that prevent it from being returned to stock with the original parts, then I'll again stick with conventional oil. Any of the kits I saw in the old days required modifications.
On a related topic, I see a lot of discussion here about using heavier oils and I am definitely not in support of that. What you have to consider is that the renesis rotary dumps a huge amount of fuel into the system from a cold start and continues to remain very rich for the first couple of minutes. The injection system is designed around a 5W20 oil, which means if you use any heavier oil, a 10W or higher, it will not flow as readily at startup, causing reduced lubrication during the most critical stage of warm up. In addition, flow properties for multi grade oils of different weights behave far differently from one another. If you use a 5W30 for example, it will not flow as readily at high temps as the 5W20. As a result you get reduced oil flow at high temps which provides less lubrication precisely when it needs more. Folks using a 10W30 oil or higher are starving the injection system throughout the operating range. In a typical piston environment, using a different weight based on season and/or service severity makes sense, but in an injection environment the same philosophy does not apply, the lubrication is not being delivered in the same manner. I won't use anything but a 5W20 oil. Just because people use it and say, gee, nothing bad happened, doesn't mean they haven't done damage or more importantly that it is somehow better. Bottom line, as you say, it's a personal choice, but those are my reasons and they are all valid. Given the RX-8 uses an electronically controlled metering pump, it may be possible to modify the profile for use with other grades of oils, but I haven't seen anything on that topic.
As far as Mazda's synthetic oil, the container specifically states "not for rotary engine use". This is the first I have heard of a rotary synthetic marketed anywhere on the planet by Mazda. If they in fact marketed a synthetic that was designed for use in the rotary, why would they not advertise that and sell it in the US? It makes no sense. All manufacturers are in business to make money and I don't see how they would pass up the opportunity especially with no competition.
One final point has to do with oil compatibility in general. I have no issue using different brands of oils in 4-stroke engines, but again, this is not a 4 stroke. Regardless of oil base, manufacturers all have proprietary formulas and there can be reactions between formulas, based on additive incompatibility. I saw this first hand back in my snowmobile days. I switched from Polaris Gold to Amzoil and then the filter in the oil reservoir plugged up, starving the injection system, resulting in a seizure. When the filter was removed, it looked like there was a thick snot all over the outside, which prevented flow. This took a long time to develop as well, which I found surprising. Mixing brands of oils in an injection environment is not a good idea. If I am forced to switch brands, I will flush and drain at least twice before extended operation. I think part of the issue with the sled was that the oil was added to the reservoir, where it mixed with the other oil. Far less would be left in the rotary, but there is still a significant amount of oil left inside the rotors after draining the sump. Multiple fills and short runs enable dilution which hopefully gets flushed well enough to prevent problems. Personal experience is what changes my view here. There have been plenty of folks who have switched back and forth with no problems, but not me.
I understand where you're coming from, and it's not my goal to convince you, but snowmobile experience is going to have limited application here. For example, in snowmobiles oil is injected into fuel, not directly onto the libricated surface.
Engine oil compatibility hasn't been an issue in 20 years.
The injection system uses a positive displacement pump, viscosity is not really a factor in its throughput.
If you're concerned about deposits, focus on ignition health and using clean gas. The rear of the moving combustion chamber is always rich, that's where problems start.
I also get where you're coming from. However, the Renesis engine is port injected, not directly into the combustion chamber, exactly the same way as in snowmobiles.
a more accurate prognosis is; severely constipated.
the first sign of someone who has no idea of what they’re talking about is an inordinate affection to go on and on gushing great volumes over the oil subject.
it’s just oil, get over it already and move on to much more important minutia.
and to prove my expertise in such matters; you’re talking to the guy who in his teens always hand washed and waxed his car moving the sponge in the direction of airflow so the surfaces scratches wouldn’t disturb airflow over the surfaces.
Trust me, you have no idea how deep the cavity goes, but ultimately regardless of the depth and breadth it eventually is a dead end with a one-way sign pointing in the opposite direction.
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Most of the people on this forum who claim "oil is oil" have not had much, if any, 2 stroke experience. If they did, they would not make that claim. Just the opposite is actually true, with 2 stroke oil, if you have opened up many 2 strokes with all kinds of use patterns, oil brands, etc. But, what is also true is that there is less difference in 4 stroke oil performance than 2 stroke. But "oil is oil" is not, and has never been true. There may not be enough of a difference in most engines for most operators to notice over the lifespan of the engine in question, but there are differences. However, getting into the weeds debating which oil is best for this or that, can get into minutiae that creates more impact in your mind than what actually is present in your engine. I am sure there are differences in various 4 stroke oil brands and weights as far as the RX8 is concerned in the combustion chamber. Because of the total loss system used.
All 4 stroke oil burns crappily, compared to 2 stroke oil. That is true. 4 stroke oil used in a total loss system is not the best for a number of reasons.
To the OP, Mazda used oil injection, with similar pump operation in earlier rotaries, and recommended everything from 5w-30 to 20w-50. Their oil recommendation chart was exactly the same as piston engine charts in those days. The viscosity of the oil you use will not matter to the oil injection system's delivery rates. There is a Mazda published RX8 oil viscosity chart floating around the internet, I believe from Australia, that looks almost identical to the charts of 30 years ago.
It sounds like you have a nice car and want to keep it that way. Good for you. The Sohn is 100% reversible if you decide to go back to stock. I recommend it to you, based on what I know about 2 strokes, and 2 stroke oil. I also recommend increasing the amount of oil used in the chamber, either through premixing, increased injection rates, or both. But, injecting more oil pan (4T) oil than stock, at the rates that a difference in longevity can potentially be expected, will most likely be problematic in other areas, like spark plug life, cat life, and overall engine internal cleanliness. Which makes the Sohn a more sensible modification.
Again, those on this forum who scold people who want to or have installed a Sohn, have little to no 2 stoke experience. They will claim "there is no evidence" that it works better. They also have no evidence that it doesn't work better either. So, do what you feel is best, and continue to ask questions. Its your car. Some here will spend time with you, and will spend that time wisely. If you have 2 stroke experience, you are already ahead of many long timers here as far as understanding what could benefit this engine.
Team RX8, you are a very strange man. I am not entirely sure exactly what your point was or is.
Kevink0000, thanks for your input. Yes, racing almost anything will give you first hand knowledge many people don't have the benefit of. In 10 years time I saw a lot of changes in oil technology and profound impact on engine wear and deposits. We had spare engines that got swapped out when something went awry, almost always due to oil. Delivery issues were the primary problem, so it was tough to tell what impact oil selection played. However, we routinely rebuilt engines based on conditions so I did get to see a lot of real wear conditions in otherwise sound engines. Number of service hours, oil being run, weather conditions, etc, all played into the rebuild equation. Evaluation of how each oil performed was important to winning races, so yeah, oil is not oil. I will continue to follow this, since I want to better understand what direction to go. If the Sohn is 100% reversible, then it is the best choice in my mind. I don't know that I will ever change it back myself, but for collector value as the car ages, it is important to retain the original parts and have a car that can be claimed as 100% stock original. Will this car have collector value eventually? Unlikely in my lifetime, but my son will inherit the car at some point and I'd like to do the best job I can in preserving its value.
And here are some interesting tests. Not "conclusive" by any means, but here is some "evidence" that is contrary to the myth that "all oils are the same". This type of test is not representative of all types of wear in an engine, or even most types of wear. But, it does represent wear of a certain type, and how different oils responded to this specific test. He even tested 2 stroke oil, and the lubricity of raw fuel.
Most of the people on this forum who claim "oil is oil" have not had much, if any, 2 stroke experience. If they did, they would not make that claim. Just the opposite is actually true, with 2 stroke oil, if you have opened up many 2 strokes with all kinds of use patterns, oil brands, etc. But, what is also true is that there is less difference in 4 stroke oil performance than 2 stroke. But "oil is oil" is not, and has never been true. There may not be enough of a difference in most engines for most operators to notice over the lifespan of the engine in question, but there are differences. However, getting into the weeds debating which oil is best for this or that, can get into minutiae that creates more impact in your mind than what actually is present in your engine. I am sure there are differences in various 4 stroke oil brands and weights as far as the RX8 is concerned in the combustion chamber. Because of the total loss system used.
All 4 stroke oil burns crappily, compared to 2 stroke oil. That is true. 4 stroke oil used in a total loss system is not the best for a number of reasons.
To the OP, Mazda used oil injection, with similar pump operation in earlier rotaries, and recommended everything from 5w-30 to 20w-50. Their oil recommendation chart was exactly the same as piston engine charts in those days. The viscosity of the oil you use will not matter to the oil injection system's delivery rates. There is a Mazda published RX8 oil viscosity chart floating around the internet, I believe from Australia, that looks almost identical to the charts of 30 years ago.
It sounds like you have a nice car and want to keep it that way. Good for you. The Sohn is 100% reversible if you decide to go back to stock. I recommend it to you, based on what I know about 2 strokes, and 2 stroke oil. I also recommend increasing the amount of oil used in the chamber, either through premixing, increased injection rates, or both. But, injecting more oil pan (4T) oil than stock, at the rates that a difference in longevity can potentially be expected, will most likely be problematic in other areas, like spark plug life, cat life, and overall engine internal cleanliness. Which makes the Sohn a more sensible modification.
Again, those on this forum who scold people who want to or have installed a Sohn, have little to no 2 stoke experience. They will claim "there is no evidence" that it works better. They also have no evidence that it doesn't work better either. So, do what you feel is best, and continue to ask questions. Its your car. Some here will spend time with you, and will spend that time wisely. If you have 2 stroke experience, you are already ahead of many long timers here as far as understanding what could benefit this engine.
Wasn't there some concerns about the Sohn adapter not injecting enough oil as it's not pressurized and rather relies on gravity drainage? Supposedly it didn't work out well in some racing applications.
On the street, it's probably fine but there is still no concrete evidence that it works better. Most of it is theory. Good theories, but theories regardless.
Never got into it because you know, S2 and all that.
Wasn't there some concerns about the Sohn adapter not injecting enough oil as it's not pressurized and rather relies on gravity drainage? Supposedly it didn't work out well in some racing applications.
On the street, it's probably fine but there is still no concrete evidence that it works better. Most of it is theory. Good theories, but theories regardless.
Never got into it because you know, S2 and all that.
In my opinion, the idea that the OMP gets pressurized oil was debunked when another RX8 owner tested the OMP port on youtube and found 0 pressure there, all the way up to redline. It is linked in the OMP modification thread. Also, when you take apart the front cover, you can see the factory omp feed is gravity flow through an air/oil separator. That wouldn't work well, obviously, if it was pressurized with oil pressure. Mazda rotaries have never used a pressurized OMP feed until the S2.
There have been reports of racers blowing engines with Sohns, the only person I have heard this from is Brettus. I have looked for other examples but found none. That doesn't mean there are none out there. There may be an issue with this setup under high G conditions in racing, and I am only speculating here. Sohn designed these adapters for rotary use in aviation, FWIW. More Gs than a car can produce.
Also, there is not any concrete evidence that it doesn't work either. The theories put forth against its use are not substantial, in my opinion, especially when compared to theories for its use.
Sometimes concrete evidence is a long time coming. If we all waited for concrete evidence before modifying our cars in any way, we would likely do nothing to them at all. When you choose a new brand of tire for your car, do you have concrete evidence that that change will fulfill your needs? What process do you use to make that choice? Concrete evidence? Where do you find it?
Also, for many, many years this was just a theory. Right up to the point that it wasn't anymore. Again, sometimes concrete evidence is a long time coming.
Last edited by kevink0000; 02-09-2021 at 07:41 AM.
...and that's why I - for feel good reasons and based upon RX-7 and -8 experience:
(1) use xW30 or better (xW40 or xW50) conventional oil (living in a cold climate I favor 5W30 over 10W30 for easier startup and oil flow up to those "pistons")
(2) change xW30 oil often between 1-3K miles
(3) add a JASO-FC or -FD rated 2-stroke oil to the gas tank (~1 oz per 2.5 US gallons is what I use)
(4) run 91 or better RON octane gas from a reputable gas station
In my opinion, the idea that the OMP gets pressurized oil was debunked when another RX8 owner tested the OMP port on youtube and found 0 pressure there, all the way up to redline. It is linked in the OMP modification thread. Also, when you take apart the front cover, you can see the factory omp feed is gravity flow through an air/oil separator. That wouldn't work well, obviously, if it was pressurized with oil pressure. Mazda rotaries have never used a pressurized OMP feed until the S2.
There have been reports of racers blowing engines with Sohns, the only person I have heard this from is Brettus. I have looked for other examples but found none. That doesn't mean there are none out there. There may be an issue with this setup under high G conditions in racing, and I am only speculating here. Sohn designed these adapters for rotary use in aviation, FWIW. More Gs than a car can produce.
Also, there is not any concrete evidence that it doesn't work either. The theories put forth against its use are not substantial, in my opinion, especially when compared to theories for its use.
Sometimes concrete evidence is a long time coming. If we all waited for concrete evidence before modifying our cars in any way, we would likely do nothing to them at all. When you choose a new brand of tire for your car, do you have concrete evidence that that change will fulfill your needs? What process do you use to make that choice? Concrete evidence? Where do you find it?
Also, for many, many years this was just a theory. Right up to the point that it wasn't anymore. Again, sometimes concrete evidence is a long time coming.
As I mentioned, I never studied the Sohn adapter due to having an S2. I will have to take your words for it.
Testing theories is great when you have the extra cash to do so. Otherwise, not so much.
Interesting. One last comment from me on oil. Aside from inherent advantages of synthetics, the issue of compatibility still concerns me. I could cite a bunch of studies and related links to articles, but the bottom line is that historically there was concern over base incompatibilities. While that in large part no longer exists, additive incompatibility remains an issue, which is why I will flush my system if I have to change brands. Each formulation is proprietary, so even if you are a chemist, you can't possibly know the possible reactions between brands. One article I read put it very well. The "brewmasters" who formulate new mixtures in most cases conduct extensive compatibility studies. By mixing oils of different brands, you are essentially creating a new formula without the benefit of any compatibility testing. I suspect the risk is very low, just like covid-19, but I ain't takin' that chance either .....
see, here we go again, it’s always the same thing, usually with the same people (me too), yet it’s still just oil
pouring oil in the tank while adding gas is not premixing; it’s a hope and a prayer, more like kidding yourself when the vehicle in question has a saddle bag fuel tank; they nervously laugh and say “oh, it will all get over to the other side equally”. No, premixing is a 5 gal gas jug, adding the measured oil, adding 5 gal fuel, shaking and mixing well, and pouring in the tank.
airplane engines are held to very high standards, including limiting hours before a full rebuild is required. The Renesis version doesn’t have a MOP controller, just a manual setting. Where did they set it? There are a few Renesis airplane engines out there, but not very many that I ever hear of or see. There are a lot of other factors with them too, but then the term “data collection” gets tossed around without any consideration for them
“done blowed up” means nothing, especially for a turbo application, but again “science”, “data collection”, you know; serious business. The first thing any of the pro racing rebuilders do is to put a block off plate over the MOP mount because premix is the racing default without exception. Real premixing, not the hope and a prayer kind.
back in the early days on here, Merlin and all the other magic elixer potion theorists raged on and on; they were the first to sell off their RX8s and never heard from again ...
and of course if I really want to see people running around with their hair on fire then all I have to do is mention “20W50 engine oil” and instant flame-on
.
Interesting. One last comment from me on oil. Aside from inherent advantages of synthetics, the issue of compatibility still concerns me. I could cite a bunch of studies and related links to articles, but the bottom line is that historically there was concern over base incompatibilities. While that in large part no longer exists, additive incompatibility remains an issue, which is why I will flush my system if I have to change brands. Each formulation is proprietary, so even if you are a chemist, you can't possibly know the possible reactions between brands. One article I read put it very well. The "brewmasters" who formulate new mixtures in most cases conduct extensive compatibility studies. By mixing oils of different brands, you are essentially creating a new formula without the benefit of any compatibility testing. I suspect the risk is very low, just like covid-19, but I ain't takin' that chance either .....
The incompatibility issue, in terms of running one oil, then switching to another, isn't an issue, if it were there would be hundreds of thousands of various brands and types of engines imploding because the owner went to the dealer for this oil change, to a speedy place for the next one, did the third one in the driveway with yet another brand of oil. In our cars we know we can't do a complete change with just a drain and fill plus filter, way too much remains in the engine. So while I certainly won't criticize you for doing a "flush" if changing brands, we all do things that make us feel better about our vehicle care, I highly doubt there is any issue. If I decided to change viscosity and had a good reason behind it, I'd likely do a short change to get to the new desired viscosity sooner than 3,000 miles, but beyond that not something I'm worried about.
01-07-2021, 05:22 PM
