DreamWarrior

Maybe this is a dumb question, but can anyone explain why the Rotary needs to consume oil? In a piston engine, the ring is lubricated with oil, yes? The ring is inside the cylinder, yes? And therefore when the gas combusts in the cylinder, isn't some oil going to be burnt there too? I'm not very knowledgeable when it comes to engines, but I don't understand why the Rotary must burn so much more than a piston engine.

lefuton

in pistons engines, the combustion chamber at the head of the piston is separated from the bottom part of the piston/crank/connecting rod by piston seals. these seals are rings that fit into a groove near the head of the piston and fill up the space between the piston and the cylinder wall, combustion on one side, lubrication on the other. piston engines tend to burn oil too when those rings crack/break/wear down etc.

in a rotary, the apex seals (at the 3 corners of the rotor) need to be lubricated. however, combustion occurs on both sides of the seal so you have to inject oil into the chamber with the air and fuel to lubricate the seals, thus it burns more oil.

wakeech

...but now that the exhaust ports are located on the side housings, the apex seals needn't have so mcuh oil for lubrication... what, something like less than half the last 13B?? it's getting less and less all the time: it's not something to worry about from a cost stand point, or a "am i going to run out of oil?" issue, it's really just something to battle with as an engineer in charge of getting the RENESIS past emissions tests.

Titanium Grey

A quick thought.

Would a double apex seal be possible?

Widen the seal slightly and cut a runner along the top edge then inject the oil into the runner.

OK, the leading edge wont get direct lubrication but it should be enough and perhaps it would further reduce oil consumption and emissions.

wakeech

hmmmm... there are 2 and 3 peiced apex seals, but those are all cut so that the seal spreads in two or three directions (to each side and up)... it's obviously a good design for the reason you pointed out, but there's gotta be a reason they can't do that....
maybe the oil between the seals would cook and stick, causing the seal to score the block??? i dunno, just throwing out ideas... i need to sleep

maxcooper

The rotary uses oil injection to get some lubrication into the combustion chamber for the apex seals and probably also for various other areas outside of the path of the side seals. It would be hard to do that via other means.

Double apex seals probably wouldn't work because they would be too fragile if they were small enough to both stay in contact with the rotor housing at all times. And besides, it would still burn some oil that way and the current injection systems work fine, so what's the point. You might even be able to use some apex seals with little oil passages in them, but that would also weaken them, and again Mazda already has a system that works fine.

I think the RENESIS needs less oil injected because the absence of peripheral ports keeps the injected oil in the chamber, rather than flinging it out the exhaust port at the end of each combustion cycle.

Just check the oil when you get gas. It is okay if you are dressed up and miss this step for a fill-up or two here and there. You probably won't need to check as often with the RENESIS since it burns less oil. It isn't that hard to keep it topped off if you are used to doing it. Previous RX-7s have had idiot lights for low oil level if you forget, but they only come on if you are a quart or so below the minimum fill mark, so you shouldn't run into that normally. I think it even buzzes at you so you can't ignore it.

-Max

DTECH-RX

Has anyone asked this question to one of the Mazda techs at any of the tech briefings or Mazda Rev It Up events? Just curious.

bureau13

There you go...fuel dillution in the FD seems to be pretty bad. I get a distinct fuel smell in my oil at pretty moderate intervals. I have no idea if the Renesis will be any different, but according to some of the things I've read, synthetics (in particular Royal Purple, which happens to be what I use) tend to not compromise their lubricating abilities in the presence of gas. This, and the fact that I have turbos, and finally the fact others have alluded to in that everyone has a friend whose engine died after synthetics but nobody in the first person seems to have that problem...well, all those are why I went synthetic.

jds

bureau13

Racing Beat is a distributor for a number of synthetic oils, and in fact has been for years, but never made that claim about any of the others.

jds

evel333

I still don't use synthetic motor oil because I still fear buying a brand that doesn't burn off well. Until I see some lab proof through extensive testing which brands burn clean and which do not, I'll stick with dino juice.

However, I do use synthetic 2-stroke oil in my fuel as its very nature is to be consumed in the combustion process. Since the oil is mixed in with the fuel, you guarantee lubrication to almost every nook and cranny within the combustion chamber.

bureau13

Can you show lab results indicating that synthetic motor oils do NOT burn well? Frankly, this high ash content, not meant to burn stuff is more myth than reality IMO. A while back, a Royal Purple rep who happened to be an RX-7 owner and participant on the "big list" posted a detailed lab report on ash content and numerous other things and the synthetic was no worse than the benchmark non-synthetic oil. I seriously doubt Mobile 1, or Redline, etc are any worse in this regard either, although I'll be perfectly willing to eat my words when somebody shows up with lab results saying otherwise.

jds

StealthTL

iTrader: (1)

I absolutely agree with Mr.evel33, a fine synthetic 2-stroke oil, with its 'super-lubricity' will be joining my premium at the pumps.
Mixed about 200:1 ratio, it can do no harm. Two stroke engines actually develop more power as a side benefit, due to the oil film sealing the chambers more efficiently.
Red Line makes a full synthetic that burns absolutely clean at 50:1, and has the best lubricity in the business - they sell it as 'Kart' oil, Racing oil and 'Superclean Two-stroke'.
S

evel333

No I can not, and it's that very uncertainty that I choose not to experiment with my engine and cats until I am sure. There is a reason why, during the RX-7's run, that Mazda recommended dino juice. Perhaps that recommendation may be different this time around with the RX-8, but until owners in the US can confirm, or perhaps members like East Moon and JSG, it's only speculation what Mazda will say.

evel333

This is not to say that I'm arguing against the use of synthetic or anything remotely like it, nor am I trying to convert anyone to dino. All I'm saying is that I personally choose not to use it. That's all. If you've been using synthetics thus far for your rotary and have had no ill effects, then great, I am happy for you. You can continue doing what you've been doing, and I'll continue what I'm doing.

(ugh! that's the problem with this tired old topic)

bureau13

My only issue wrt synthetic in the Renesis is...is there any tangible benefit, given that you're probably going to change it often anyway? For the FD, I think the answer is a resounding YES, due to the turbos. However, with a NA motor...I don't know.

jds

evel333

Resounding yes? What are you talking about? This has nothing to do with turbos.

The problem has always been unique to the rotary in that If a particular brand of synthetic oil does not burn off in the combustion cycle, it, or what ever is left of it, will be flung out of the peripheral exhaust port and will eventually clog the pre-cat or main cat, causing a back up in exhaust flow, increasing heat in the area of turbos and exhaust manifold.

bureau13

Again, you're citing "data" that at best is unconfirmed. I have seen no REAL data that indicates that synthetic does not burn in the combustion cycle, and some that suggests that it does. Second...we're getting a little off topic here I think...regarding the FD, which has turbos, the question of whether to use synthetic is very much relevant to the turbos. They are the items receiving the bulk of the benefit, so if you're looking at it from a cost/benefit perspective, they ARE most of the benefit. Hence my comment about not knowing if synthetic makes sense for the RX-8, even putting aside the age-old discussion of it with rotaries in particular.

jds

evel333

No citing at all, and certainly no more "confirmed" than your previous comments in defense of the use of synthetics. You are obviously quite set in your decision--good for you--no need to defend them from the likes of me. And please don't think I'm trying to convince you that synthetics are bad, or persuade you to switch to dino, because I respectfully am not. All I was saying is that I choose not to use the stuff. My reasons are my reasons and I won't be swayed any less than you will without any proof.

wakeech

...other than by owners, not to mention Mazda, whose had trouble with running synthetic oil... i know that there are those who have no problems (Racing Beat lays claim to this, but they're a Royal Purple distributor) and i know that there are those who say they have had a problem with fouled cats, plugs, etc...

bureau13

But you see, this is the problem. Who are these people with clear synthetic-related problems? Where are they? Go post on the RX-7 forum or on the mailing list and try and find anyone with real problems...you will find at most a few who will make comments like "I started using synthetic and then I had to rebuild my motor, so synthetic must be bad." Of course, most FD owners who use dino-juice have to rebuild their motors also. As for fouled cats and plugs....find an RX-7 owner who hasn't had any problems with fouled cats and plugs? Its not exactly uncommon to have these problems, and by far most owners do not run synthetic oils.

jds

bureau13

Well, if all you were saying was that you choose not to use it I would never have posted a response. I myself mentioned in this thread that I didn't know if it would be worthwhile to use on an RX-8 even if the bad for rotaries stories are false, so I certainly don't care if you or anyone else uses it or not. Earlier in the thread you stated as fact that synthetics don't burn well. THAT is why I responded, and that is what I am arguing against. Use it, don't use it, I really could not care less...I just wish people would stop using tired myths with no supporting data to justify their decisions.

jds

Maestro

Mazda spent millions to make this 5W-30 Mineral oil.

So use it !

If was mean't have synthetic oil it would come with it.

Vaillant

So....Mazda has deliverd the RX-8 to some customers in Japan, right? And they came with owner's manuals, right? Which means we should have an answer straight from Mazda on what they recommend for the RX-8.

So, someone who has got one, pipe up! What's the answer? What oil is recommended?

Anyone?

Hello?

ECHO...Echo...echo...

Maestro

I work for Mazda all rotary engines come with Mazda 5W-30 Mineral oil.

If you want more you can buy MazdaSpeed 0W-30 Mineral but its really expensive.

I can send you some info in pdf format if you would like on the 5W-30

Vaillant

Is it the standard SJ oil that you can find anywhere? Or is it something special? I'm assuming it's just normal 5W-30.