The role of the oil in the rotary engine..

Quick_lude · 07-04-2003, 12:09 AM

Ok so in an attempt to clear up some confusion and find out what the best oil is for the rotary, here's my question. What exactly is the role of the oil in the rotary engine? Lubrication and cooling I guess.. What about the bit of the oil inside the combustion chambers? Is it better if the oil burns easier or not? What temps are achieved in there? Could the synthetic oils be "worse" for the rotary because they typically have higher flash points and thus don't burn as well?

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Efini 8 · 07-04-2003, 02:22 AM

what is the oil application - for what rotary engine, forced induction?, engine oil?

Quick_lude · 07-04-2003, 11:54 AM

Well I though every version of the rotary, NA, FI, Renesis needs oil in the chamber to lubricate seals?

Which oil to use is what I'm trying to figure out.. regular or synthetic.

eccles · 07-04-2003, 12:14 PM

The oil is indeed an integral and critical part of the cooling system on a rotary. The rotor surface comprises a far larger percentage of the total combustion chamber surface area than the piston in a reciprocating emgine, thus it needs greater cooling. This is done by a couple of nozzles in the eccentric shaft which spray oil over the inside of the rotors, from where it drains back into the sump for reuse.

As for seal lubrication - on a piston engine, the rings are lubricated by the thin oil film that's left on the cylinder walls every stroke; this same effect lubricates the rotary's side seals, but the apex and corner seals never sweep an area that is exposed to oil at any stage of the cycle, so it is necessary to introduce small quantities of oil into the intake charge to lubricate those critical seals.

I can't say one way of the other for sure on the burning properties of dino vs synth - I have seen conflicting reports so I'll go with Mazda's statement that the Renesis is designed for non-synthetic oil. (They even emphasised that point on the tech highlights CD.)

Quick_lude · 07-04-2003, 01:03 PM

So the oil gets recirculated? Thus wouldn't you want an oil that doesn't burn but lubricates and then gets recirculated?

eccles · 07-04-2003, 01:25 PM

Quote:

Originally posted by Quick_lude
So the oil gets recirculated? Thus wouldn't you want an oil that doesn't burn but lubricates and then gets recirculated?

The oil that's sprayed into the inside of the rotors returns to the sump, just like the oil that's forced through the bearings, etc. The minute amount that's injected into the intake is a total loss - it burns up in the combustion process and exits with the exhaust.

wakeech · 07-04-2003, 04:37 PM

Quote:

Originally posted by eccles
The minute amount that's injected into the intake is a total loss -

...i thought it was metered in through a bung in the rotor housings...??

but this oil is specifically to lubricate the apices, and nothing more... it's just a simple fact that you cannot do this without getting oil into the combustion charge.

IGOZMZM · 07-06-2003, 01:07 AM

Mazda says to use 5w-20 NON-synthetic oil. This information comes from the mazda cd floating around the forum.

RX-8 Zoomster · 07-06-2003, 01:56 AM

Quote:

Originally posted by wakeech

...i thought it was metered in through a bung in the rotor housings...??

but this oil is specifically to lubricate the apices, and nothing more... it's just a simple fact that you cannot do this without getting oil into the combustion charge.

Lubrication and metering through a bung hole?

I don't think I'm going to touch that one.

rotarygod · 07-08-2003, 01:54 AM

The old rotaries originally injected oil into the carb. Later with fuel injection came direct injection straight into the rotor housings. There were 2 located here and 2 located on the primary intake runner tracts. The 3rd gen RX-7 had just 2 on the rotor housings. The Renesis uses the rotor housing location but instead of just one per rotor there are now 2 per rotor. They are side by side. This location allows oil to directly touch the apex seals as they pass by. The side by side location on the Renesis enables oil to get to much more total area of the apex seals than just one can provide. This in turn lets less oil be injected into the engine since it is being used more efficiently. This is what makes the side port exhaust possible. Mazda tried the side port exhaust very early in the development of the rotary engine but found that the exhaust ports easily got clogged with carbon deposits at the back bend of the port. The easiest solution was to make the exhaust a peripheral port. This way the carbon would go straight out of the engine. In truth this wouldn't have been much of a problem after the mid '80's when fuel injection came into use. Who knows why Mazda waited so long to try again. I guess old habits die hard. The oil mixing with the old carbs was not very well dispersed and had a tendency to clump. It wasn't uncommon to need a quart of oil every 700 or so miles. Then add in the early carbon apex seals and their very fast wear rate contributing to more sediment and you had a big problem. This really isn't a problem at high revs but moreso at typical daily driven rpm's. 2 cycle engine oil is frequently pre-mixed in with gas by many RX-7 owners while the oil metering system is just disconnected. 2 cycle engine oil is designed to be used this way though and is designed to burn very well. Just a little bit of history for you guys who didn't already know.

wakeech · 07-08-2003, 02:24 PM

Quote:

Originally posted by rotarygod
The easiest solution was to make the exhaust a peripheral port. This way the carbon would go straight out of the engine. In truth this wouldn't have been much of a problem after the mid '80's when fuel injection came into use. Who knows why Mazda waited so long to try again. I guess old habits die hard.

...you can also make a sh*t load of power out of p-ports whilst still passing emissions... what would you do??

ibfubar2000 · 07-09-2003, 04:08 PM

staright from mazda rx-8 workshop manual<p>Item Recommended oil
API service SL
SAE viscosity 5W-20
ILSAC GF-3 <p>
Oil capacity (Approx. quantity)

L {US qt, lmp qt}

Item Oil capacity (Approx. quantity)
Oil replacement 3.6 {3.8, 3.2}
Oil and oil filter replacement 3.8 {4.0, 3.3}
Engine overhaul 5.0 {5.3, 4.4}
Total (dry engine) Standard power: 6.1 {6.4, 5.4}
High power: 6.9 {7.3, 6.1}

rotarygod · 07-09-2003, 05:34 PM

5W20 is what Honda and a few other manufacturers recommend as well in many of their cars. They like to recommend this because it is a lighter oil that helps gas mileage since it takes less effort to overcome the viscosity drag within the engine. Even their F1 engines use this! I wonder if that's why Honda F1 engines are so fragile and break alot? Hmmm...

I once spoke with a Honda sponsored motocross (whatever the crotch rocket on road race bikes are called) team mechanic about the light oil. He said that the formulas used today are much better than they were several years ago. Because of this the lighter oils will still do their job and not break down, even in high temperatures. The old oils would break down faster if they were out of their recommended temperature range so a heavier oil was needed in hotter weather. Just what I heard but I'm not the expert.

neit_jnf · 07-10-2003, 01:33 PM

I was wondering that instead of disabling the oil-metering system and using premix, what if someone custom made a small oil tank and installed the oil metering pump there? Then it could be possible to use 5w20 non-synthetic oil in this tank while using full synthetic in the engine. If the small tank was say 1-2qt size then it would need to be refilled every 10-20k miles and since the oil was solely for metering it will never get contaminated and never need to be changed. Of course the engine oil still needs to be changed and everything. I think this would be optimal because the lubrication and oil metering system would operate as Mazda designed it. Anyone thought of this before or even did it?

babylou · 07-10-2003, 01:39 PM

I like this idea!

Quick_lude · 07-10-2003, 02:26 PM

I will still use at least a 30 weight oil.. 0w30 or 5w30. The 20 weight oils have been developed mostly for CAFE NA standards. The jury is still out how well these oils will protect the engine over the long, 100K miles plus, haul.

What does Mazda recommend for oil viscocity in Europe and/or Japan?

For most European Honda's 5w40 is recommended.

OrangeBingo · 07-10-2003, 02:43 PM

Looks like I can stick with Castrol GTX after all.

RX-8 Zoomster · 07-10-2003, 02:50 PM

Quote:

Originally posted by Quick_lude
The 20 weight oils have been developed mostly for CAFE NA standards. The jury is still out how well these oils will protect the engine over the long, 100K miles plus, haul.

Whether the jury is still out or not, it must be up to Mazda's standards for the rotary. If Mazda's recommended oil is 5w-20, according to the owner's manual, then that is what I'll use. IMO, that weight is fine, especially if you are changing it every 3000 miles.

After the warranty period, who knows, I may change, but the 20 weight should be fine then too.

Quick_lude · 07-10-2003, 03:00 PM

If you think that a certain weight of oil is ok because you will keep to a short interval then you don't know how the oil functions. shrug
You can break down a twenty weight oil during the first 100 miles of an interval.

It's the base stocks, sythetic PAO's, esters and additive package that determine the oils ability to function over the longer interval.

Heavier, 30 or 40 weight oils typically hold up and do NOT shear at extreme loads/temps.
So once again, if someone has a European or Japanese version of the manual, please let us know which GRADE of oil is recommended.

RX-8 Zoomster · 07-10-2003, 03:17 PM

Quote:

Originally posted by Quick_lude
If you think that a certain weight of oil is ok because you will keep to a short interval then you don't know how the oil functions. shrug
You can break down a twenty weight oil during the first 100 miles of an interval.

It's the base stocks, sythetic PAO's, esters and additive package that determine the oils ability to function over the longer interval.

Heavier, 30 or 40 weight oils typically hold up and do NOT shear at extreme loads/temps.
So once again, if someone has a European or Japanese version of the manual, please let us know which GRADE of oil is recommended.

I know how an oil functions. I'm not saying that any weight is OK just becuase of a 3000 mi. changing interval. I AM saying that the 5w-20 weight would be fine with me, because that is what Mazda IS RECOMMENDING for this engine. Along with a 3000 mil changing interval.

Do whatever you want with your engine. It's your car. I will follow Mazda's maintenance schedule - 3000 mile oil changes and I will most likely use the 5w-20, especially while it's under warranty. And I will top off the oil regularly if it needs it. If the engine is subjected to more extreme temperatures or loads, then I MAY have to change the oil more often. I do that will all my cars, regardless of weight.

Don't belittle me, by saying that I don't know enough about oil. Or just because I don't use what you may use or know as much about oil that you do, that I don't care. You are emplying that I care less about my engine and how long I want it to last. You obviously know more about oil than me, but I don't care. I appreciate the added info you provided.

In my car, I will most likely use the manufacturer's recommend weight and I will definately follow it's scheduled maintenance plan, And with me following Mazda's recommendations, you know what, I think my engine will last as long as yours.

rotarygod · 07-11-2003, 12:34 PM

As far as the seperate reservoir for injected oil goes, it already exists. There is a company out of Florida who makes an adapter to fit the 12A/13B family of engine oil metering pumps. It is actually an aviation rotary company. It simply just draws oil from a seperate tank and injects it leaving the lubricating engine oil to do its job. Most people just fill a small tank such as a catch can with 2 cycle motor oil and check the level periodically. Fantastic product and less than $100.

wakeech · 07-11-2003, 12:49 PM

Quote:

Originally posted by rotarygod
As far as the seperate reservoir for injected oil goes, it already exists. There is a company out of Florida who makes an adapter to fit the 12A/13B family of engine oil metering pumps. It is actually an aviation rotary company. It simply just draws oil from a seperate tank and injects it leaving the lubricating engine oil to do its job. Most people just fill a small tank such as a catch can with 2 cycle motor oil and check the level periodically. Fantastic product and less than $100.

that's the best idea i've heard yet...much better than running mix gas.

rotarygod · 07-11-2003, 01:04 PM

I found the link:

http://www.rotaryaviation.com/oil_in...p_adaptors.htm

eccles · 07-11-2003, 01:11 PM

Quote:

Originally posted by rotarygod
is a company out of Florida who makes an adapter to fit the 12A/13B family of engine oil metering pumps. It simply just draws oil from a seperate tank and injects it leaving the lubricating engine oil to do its job.

Neat idea, but I think it will require some rework for the Renesis. On earlier engines, the metering pump's rate of flow was adjusted mechanically via a pull rod from the throttle linkage, but on the Renesis it's electronically governed by the ECU. The Technical Highlights CD stresses the point that this is not a servicable item, and I suspect that removing or disconnecting it will result in a Check Engine light at best, and possibly even a drop into limp-home mode.

I think I'll stick with the manufacturer's recommended lubricant and distribution mechanism.

rotarygod · 07-11-2003, 01:18 PM

It has been electronic since 1989!