ray green

iTrader: (14)

I've been adding 8 ounces of MMO to the gas for the last 9 months, 10,000 highway miles and three oil changes on an 85 stock GSL. Before the MMO, I was adding oil to the engine a couple times between oil changes, maybe a quart altogether. But since adding the MMO to the gas my oil level never goes down. I read somewhere that most of the oil put into the combustion chamber with the gas doesn't get burned (flash point too low?) and actually returns to the crankcase. So does the MMO end up mixed with the engine oil? Is this why my 7 keeps running better and better?


Ray

nlc1179

i didnt think it kept down the oil consumption, but i think it does make it run a little better. i used to premix it in my 1st gen. i am going to in my tII also, when i get my lisence back.

erick1120

Once the oil is put into the combustion chamber from the oil metering pump it does not return to the crankcase. It is either burned or spit out the exhaust. Adding MMO to your fuel should not change the amout of oil being used unless you disabled the oil metering pump.

180sx-x

^ that wouldnt be good...

ray green

iTrader: (14)

Hah, found it! From atkinsrotary.com FAQs:

68. Does the oil in the combustion chamber burn?

Hardly any of the oil in the combustion chamber burns, it is scraped off of the cast irons by the oil rings and returned to the oil pan.

So the MMO ends up in the oil pan, right?

Ray

Wankelguy

No, it has no way to return to the oil sump unless it works it's way past the oil control rings on the sides of the rotors. If that were the case, the oil control rings would be totally shot and the motor would not even run. The purpose of the oil control rings is to keep oil from inside the rotor from making it's way into the combustion chamber in the first place.

ray green

iTrader: (14)

Of course I completely respect the knowledge posted by our forum members, but now I'm a bit confused because I also think that I should take Atkins Rotary seriously too. According to their website:

68. Does the oil in the combustion chamber burn?

Hardly any of the oil in the combustion chamber burns, it is scraped off of the cast irons by the oil rings and returned to the oil pan.

So I'm confused, does the oil get burned or not and if so how much gets burned and does the rest go back to the engine?

Can anyone sort out this apparent contradiction?

Thanks
Ray

newsflash

I'm with wankleguy,

If oil could go from the combustion chamber to the oil pan through the oil rings, then it could go vice versa, thereby completely eliminating the whole point for oil rings in the first place.

Besides, that only applies to the oil on the sides of the combustion chamber walls close to where the oil rings pass. Thus the rest of the oil would either boil off or go out exhuast *anyway*.

Jon

efi12a

My experience is that the oil control seals do in fact scavenge unburned oil to the sump. I'm not using OMP at all, totally premix, and I can tell you that my oil level goes up as miles accumulate. The premix oil I use is blue in color and my normally honey colored sump oil does get a blue tint to it. This is a well running, 5000 mile engine that was properly broken in and has excellent compression on all rotor faces. I don't quite understand it, but it definitely happens. Dave Atkins is no BS artist, I'll ask for details on this matter next time I call out to Atkins.

ray green

iTrader: (14)

thanks efi12a, another rotary misconception cleared up!
Ray

cdrad51

huh. Isn't that funny. I found this in the Haynes manual:

"Also designed into the system is an oil metering pump that feeds oil directly into the carburetor to lubricate the internal seals during the combustion process. This oil is not retrieved, thus contributing to the higher-than-normal oil consumption of the rotary engine."

Wankelguy

How so? I am not in the habit of posting "rotary misconceptions".

efi12a

Well, I can only report what I consistently observe. I think we have no conception of exactly how much oil is scavenged and how much is consumed in the OMP case. My setup is a nice test case as I do not consume or withdraw any oil from the sump for seal lube purposes yet the sump level DOES rise. I usually fill the sump to 1/2 quart low upon oil changes every 1000 miles and change it when it reads full. Now, in that 1000 miles I've burned maybe 70 gallons of gas. This translates to 70 ounces of premix oil. Since I have only had 16 ounces extra show up in the sump, most of the oil is indeed burned/consumed. Maybe 20% is scavenged. I think everyone is partially correct on this issue, it's just hard to quantify unless you have a long mileage, premix only test case to observe. Most premix only systems are race only. To clarify, I'm not using premix in place of OMP, I simply don't have the option to OMP with my hardware. I've seen the infamous "oil nozzle stripe" of unworn rotor housing surface enough to convince me that the OMP method alone can be improved upon. Unfortunately, premix alone can cause excessive oiling for low load or cruise situations. This has caused emission problems for a couple of people I know personally. I'm at 5K miles and counting and my plugs are much cleaner than they have been my previous OMP installation. I think the key is that the 2 stroke oil doesn;t carbon parts up like 4 stroke/sump oil would. I also have tight control of AFR and routinely cruise at ~14 or 14.3/1 with EGTs of 1200. This controls the carbon accumulation caused by consistently overrich fueling, I believe. I have to pull the intake manifold soon for an alternator replacement (don't ask...) and am planning on borescoping the rotor housing surfaces to see how the wear pattern is looking. I digress....

efi12a

Another data point: anybody ever observed gas dilution of the sump oil after a flooding episode? That DEFINITELY happens frequently. I theorize that there is a scavenging function by the oil seals in this case as well. There is an awful lot of linear inches of seal if you add them all up - even the slight leakage observed is within the realm of possibility, IMHO.

efi12a

Also, the net, average pressure gradient across the oil control seals is definitely from rotor faces to sump. Sorry for the multiple messages, I'm just brainstorming trying to reconcile my observations. I'll be calling Atkins tomorrow to see what their take is on this. My engine is still under warranty so I'll be inquiring on that premise, i.e., is this normal behavior and, if so, why.

ray green

iTrader: (14)

No offense Wankelguy, I just am trying to find out if the oil injected into the combustion chamber gets recycled and if so how much. efi12A is seeing the same thing that I am seeing (engine oil level rising when MMO is mixed with the gas) and he sounds like he's got it figured out (along with Atkins and probably a bunch of other knowledgable rotar heads who probably aren't bothering with this discussion). So, it seems like the Haines manual (which I read regularly) might have been wrong, along with a lot of other rotary folks (including me), about the idea that the oil is "burned"; apparently most is returned to the engine after doing its lubrication job. But if this is not the correct answer to the question I hope someone out there will let us know. And thanks to everyone for all their input.

Ray

efi12a

I just got off the phone with Dave Atkins. He relates that the transfer of oil from the intake to the sump can happen, does happen, but usually means you're running too much oil in the intake charge. He also believes that the OMP is adequate unless you're regularly running past 8K rpm. Unfortunately, I forgot to ask if this was specific to the 12A or not (I doubt it) , I was left with the impression that this was his blanket opinion regarding the Mazda rotary engine.
-Mike