Those familiar w/ the RX-8 syn oil controversy...

[mazdamonky]

Originally Posted By: d00df00d
Originally Posted By: mazdamonky
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.

Are you talking about Dexelia Ultra or Synthe Renesis? I'm not sure what Dexelia Ultra is made of, but Mazda says Synthe Renesis is PAO/ester.


I am not 100% sure which oil it is. I am just going off of some information I read a while back on the Rx7club or rx8club forums when I was doing my first bit of research on why people think Synthetic is bad for Rotaries. I believe they had a Mazda rotary engine oil similar to current Mazda 0w20. It was house branded but made by someone else obviously. Either way, I do know that there are synthetic oils made specifically for rotaries that are PAO/Ester oils and many have used them and had fine luck. As for Carbon buildup, I have been running Synthetic for the past 20k miles with 5k mile oil changes on my 85 and there is no major carbon buildup (at least no more than beforehand) when viewed from a camera inside of the spark plug hole. Today's synthetics are very different from Synthetics of many years ago.

As for Rotaries and carbon buildup, I don't think the oil really causes any major difference now days. It is more related to people who do short tripping and never get their motors nice and hot to burn off any carbon buildup. My recommendations are to get the engine up to 5-6k rpm and just drive it there for 5 minutes once every couple of weeks or to just take it for a good 30 minute drive on the freeway once a week and hit your redline at least once or twice while the motor is hot.

 

[mazdamonky]

Originally Posted By: StevieC
Originally Posted By: SubieRubyRoo
Stevie, I wouldn't say it's entirely horrible. The power density can be phenomenal, and do not have many of the limitations of piston-driven ICEs. That said, the inherent limitations and guaranteed oil consumption are negatives for a daily-driven vehicle.

If you're anal about maintenance, enjoy driving it hard, accept sub-standard mileage, and check oil levels on a frequent basis, there's nothing to completely steer you away from a rotary.


I was talking about from a longevity standpoint because of the seals and it not making it a long haul candidate. But yes a fun toy for sure.

I have driven both one from the 1980's and one now right after one another. (A friend of my dad has both). The newer one is a lot of fun.


I own an 85 and have owned an 84, 86 and 87 over the years. None of these cars have really used insane amount of oil. There are new cars that use 1 quart of oil per 1000 miles and they consider it normal. That is about the rate in which I have had to top off oil in most of my cars. My current one is about 1 quart per 1500.

I didn't buy any of the cars for fuel economy. I bought them because I think they look great and they are a lot of fun to drive.

As for long haul reliability, the N/A motors are known to do 150k+ miles fairly well on older cars. General lifespan of 1st gen's with a 12a is expected to be around 200k miles which is great for any car from the late 70's to early/mid 80s. Sadly the renesis is a gamble on engine life. I have seen many go around 80-100k while I have seen a handful make 125-150k and a select few make it to the 200k mark. Sadly all of them I have seen with over 150k miles on an original motor have been using 2 stroke since they bought the car and owned something rotary before they originally purchased the car.

 

[weasley]

I had a RX-8 (230 bhp one) for 3 years from 2004-2007 and ran it on "synthetic oil" for the whole time, no issues. However, I know what the issue is. In Japan, like in Germany, group III base oils are not considered "synthetic", so when they said "don't use synthetic oils" what they meant was "don't use PAO oils". However, this was at odds with the rest of the world, who interpreted it as "don't use PAO or group III oils". Mazda's own genuine oil (Dexelia) was a group III oil (in Europe at least)! And over here we ran 5W-30 (I used Magnatec in mine). I've read plenty that recommend using 10W-40 to protect the primary gears.

 

[d00df00d]

Originally Posted By: weasley
I had a RX-8 (230 bhp one) for 3 years from 2004-2007 and ran it on "synthetic oil" for the whole time, no issues. However, I know what the issue is. In Japan, like in Germany, group III base oils are not considered "synthetic", so when they said "don't use synthetic oils" what they meant was "don't use PAO oils". However, this was at odds with the rest of the world, who interpreted it as "don't use PAO or group III oils". Mazda's own genuine oil (Dexelia) was a group III oil (in Europe at least)! And over here we ran 5W-30 (I used Magnatec in mine). I've read plenty that recommend using 10W-40 to protect the primary gears.

Again, Mazda's own Renesis-specific oil (Synthe Renesis), only sold in Japan, was PAO/ester per Mazda.

http://www.mazda.co.jp/carlife/service/parts/detail/oil/lineup/synthe-renesis/

 

[chrisri]

Google Translator say that this is a specific PAO oil designed with carbon deposit in mind, and that it is first full synthetic oil recommended for RE. They (Mazda) obviously are aware of problem and tried to remedy it with specially developed oil that leaves very little carbon deposits.

If you can obtain that particular oil, use it. I would not use ANY PAO oil OTC in hope it will do fine.

 

[d00df00d]

Originally Posted By: chrisri
Google Translator say that this is a specific PAO oil designed with carbon deposit in mind, and that it is first full synthetic oil recommended for RE. They (Mazda) obviously are aware of problem and tried to remedy it with specially developed oil that leaves very little carbon deposits.

If you can obtain that particular oil, use it. I would not use ANY PAO oil OTC in hope it will do fine.

I'm not saying "any" PAO would work. I'm pointing out that the "no PAO" argument can't be right. The total formulation matters, as you seem to agree.

Mazda Synthe Renesis also touts ester content, as do most (all?) of the other rotary-specific full-synthetics. Maybe that's the key to making PAO work here.

Either way, the main question here is, are there synthetic oils that will produce carbon deposits in a rotary engine regardless of usage? It's certainly possible. I'm just not sure how likely it is, hence the thread.

 

[mazdamonky]

Every oil can and will produce carbon deposits in a rotary. It all depends on how you drive the car. If you heat the engine up, carbon deposits will be not really be a problem. Often times engines with high levels of carbon deposits ran standard oils but short tripped or never revved their motor. It is not about the oil used. Some oils may cause more carbon deposits than others, but even the highest carbon depositing oil won't matter if your engine keeps itself clean by getting hot and making sure to burn everything off.

 

[d00df00d]

Originally Posted By: mazdamonky
Every oil can and will produce carbon deposits in a rotary. It all depends on how you drive the car. If you heat the engine up, carbon deposits will be not really be a problem. Often times engines with high levels of carbon deposits ran standard oils but short tripped or never revved their motor. It is not about the oil used. Some oils may cause more carbon deposits than others, but even the highest carbon depositing oil won't matter if your engine keeps itself clean by getting hot and making sure to burn everything off.

Have you ever seen carbon in the intake ports, like in that Mazda TSB?

 

[quint]

I've had three rotaries; an '80, an '86, and an '87 TII. The '80 went 135K before I traded it in on an almost new '86, and a bad wreck took it out at 139K. I went out and found the TII, bald tires and needing a clutch, sitting back behind a Ford dealership, that had 75k. Bought it for half their asking price, changed the fluids, threw in a new clutch and put new tires on it, and took it to 125K when after a quarter-million miles or so of rotary ownership I finally experienced the dreaded sputtering and serious drop in power. I knew what was happening and was actually surprised it made it that far, the turbo models usually didnt.

I tore the engine down and found one apex seal on the rear rotor had cracked and started to come apart. The rotor faces had as much carbon on them as any piston top I had ever seen, but not really any more than that. There was very little carbon in the seal grooves or anywhere on (what was left of) the rear rotor apex seals. The front rotor looked similar, and the seals pretty much looked fine. This was after a steady diet of whatever dino 10w-40 or 20w-50 I had on hand. Never used synthetic in any of my Rx's.

If you've ever seen inside a rotary that was run on 2-cycle oil, they are spotless. Mazda really should have used a smaller regular sump (for the main bearings, side seals, and internal rotor cooling), and used a separate 5-10 quart tank for 2-cycle oil and let the oil metering pump draw from that (for the apex seals) instead of the main sump. Monitor it with a dash light and set off a warning buzzer when there is 1-2 quarts left and things would have been a lot better.

The marketing dept didnt want the reputation of rotaries being quirky with special high maintenance requirements which is understandable, but people popping their engines at 70k miles and having to quietly extend the warranties on replacements and tarnishing their reputation by putting out a fragile product didnt do them any favors either. Most people who owned them knew they were designed to use oil, the manuals were clear to keep an eye on it, and when it came to oil change time those who ignored it saw the dipstick with almost nothing on it. Extended OCI on an Rx7 or Rx8? You didnt get an engine full of sludge , it runs fine until it just goes 'pop', power drops to zero and you pull over and cry. Why this wasnt considered a big deal, but a separate 2-cycle tank was...I understand their intention, I just never agreed with it.

The haters can hate on rotaries all they want. The old man down the street has a mint, rust free silvery blue '85 in his garage with less than 80k miles on it, he runs 2 cycle in it, and someday that car will be mine (fingers crossed). Never cared much for the body of the Rx8 to consider getting one, but I did like the interiors and they are nice driving cars.

As far as the synthetic debate goes, yea I wouldnt bother with that debate, plenty of that on Rx forums to go around. Premix/2-cycle is the way to go. Red-line it daily, drive it like you stole it to keep it clean, and they'll do ok.

 

[mazdamonky]

Originally Posted By: d00df00d
Originally Posted By: mazdamonky
Every oil can and will produce carbon deposits in a rotary. It all depends on how you drive the car. If you heat the engine up, carbon deposits will be not really be a problem. Often times engines with high levels of carbon deposits ran standard oils but short tripped or never revved their motor. It is not about the oil used. Some oils may cause more carbon deposits than others, but even the highest carbon depositing oil won't matter if your engine keeps itself clean by getting hot and making sure to burn everything off.

Have you ever seen carbon in the intake ports, like in that Mazda TSB?


I personally have never seen excessive carbon anywhere in the intake, but yes, I almost always see carbon in the intake and even some in the motor. The carbureted engines seem to experience this the least on the intake side of things in my experience, but I have always run seafoam every oil change just because it is a little peace of mind.

 

[AntsinmyEyes]

I've been premixing mine with amsoil interceptor 2 stroke oil. its what they recommended to me. I also run it with castrol 0w40 or m1 15w50.

i deleted the oil metering pump when i first got it so no worries about extra carbon build up.

 

[d00df00d]

Not sure why this hasn't been more widely shared.

Just stumbled across this post from Mazdaspeed in 2008. It's for RX-7s, but it seems like it might be informative for the RX-8. Found it in this thread on another forum. Archive.org link because the original site has been taken down:
Quote:
Synthetic oil is not recommended, unless emissions components and oil injection are removed, and premix fuel is used.

Because the rotary uses oil injection synthetic oil could reduce the life of emission components such as catalytic converters and O2 sensors.

Also, the rotary burns oil to lubricate the the apex seals, and synthetic oil burns at a higher temp than mineral based oil. Repeated short trips may cause synthetic oil build up, leading to spark plug fouling.

Finally, oil sprayed inside the rotor cavities can contact the rotor oil seal O-rings, and oil inside the combustion chamber can contact the housing seal O-rings. Long term exposure to synthetic oil may cause these seals to swell and deteriorate.

If oil injection is removed, and fuel is premixed, synthetic oil can offer a slight amount of additional horsepower.

The O-ring issue isn't an issue for the RX-8 per Mazda.

I'm thinking the concern about emissions components should be solved by using an oil that isn't too heavily additized. Synthetics do tend to be more heavily additized than conventionals. However, few of the popular syn options are THAT heavily additized, which may be why we have yet to see this problem in a big way among RX-8 owners using synthetics. And obviously this is meaningless for decat/race cars regardless of oil choice.

The point about synthetic oil buildup leading to carbon fouling confirms the worries that some people have expressed, and seems like it might be related to Mazda's TSB about carbon buildup with synthetics. It's also easily explicable if 500º F really is the lower limit for combustion temps. And the idea that it's only an issue with lots of short trips is... pretty much what I was saying at the beginning of this thread.

So yeah. Unless RX-8s have completely different combustion dynamics from RX-7s, the moral of the story seems to be:

• If you’re always driving the car as it’s meant to be driven, you should be running a synthetic.
• If you’re always driving mildly, you might be better off with a conventional; if you go semi- or full-synthetic, stay away from the highest flash points and lowest NOACKs.
• Mixed hard/mild driving might be tricky. Go with a synthetic and ELIMINATE idling, short trips, and low RPM driving -- or go with a conventional and try not to run it too hard too often.
• If you go for a synthetic, look for something that burns clean. A low sulfated ash number might be a good guide. Ester content is good. Stay away from very high levels of metal-containing additives (Ca, Mg, Zn, B, Mo, etc.).

Any thoughts?