David Beale

I'm sorry, but I must be thick or something. I don't understand:
"ok, if you remove the oil metering pump, you can run synthetic oil because it doesnt get into your combustion chamber."
Whether you use the OMP or premix, the oil goes into the combustion chamber. With the former it's injected (dribbled), with the latter it's there with the fuel.

The RX-8 owners manual recommends NOT using synthetic. Perhaps they just want to sell more engines .

In my 2 stroke motorcycles I found synthetic worked better than non. My Can Am 175 required the head to be pulled every 3000 mi. to decarbonize. Once I switched to synthetic, it was unnecessary. No carbon built up.

paw140

See, this is the kind of thing I was asking for. Actual real-world experience. Nice observation

One thing to keep in mind, though, is that two-stroke oils are specially designed to burn w/o residue.

rotary-tt

RX-8 owner's manual on oil:

David Beale

The synthetic I use in my m/c's doesn't actually burn. It sprays out the exhaust, slightly blackened. I now have an RZ350 and a DT200 (water cooled power valved etc). I'd use it in my RX but I have an oil pan leak and the synthetic would pour out.

rzograbian

what made me go with this is because i will be running single soon and want the protection of a synthetic in my motor. its true that i dont know a whole lot about the function of the oil metering pump but while i was at Rotary Power where my motor is getting rebuilt, he told me that it cant burn in the combustion chamber so you get carbon buildup. he showed me the motor because it was all apart. he said the carbon buildup was really bad, the apex seals came out harder than normal.

rzograbian

so i have proof of what it does to the motor.

rynberg

damn forum

rynberg

Bah, it's easy for any rotary to have a shitload of carbon build-up in the combustion chambers. It doesn't take synthetic to do that.....mechanics aren't chemists either.

Besides, what the hell does going single have to do with removing the OMP? Also, do you honestly think your motor is going to last long enough with a single turbo to suffer from any oil-related failures?

rzograbian

no, i just want the added protection of a synthetic. this wasnt suppose to turn into another debate.

rynberg

And what MOST of us are telling you is that it is perfectly fine to run synthetic with the OMP. MANY of us do it. In the three years I've been a member here, no one has ever had a blown engine due to build up from synthetic oil. Even if synthetic does leave a residue, your single-turbo engine will have blown for other reasons long before it becomes an issue.

PVerdieck

This is wrong. There are synthetics that are designed to burn and are very low in ash. There are numerous companies making synthetics for 2-cycle engines.

What is true, is that synthetics have advanced a huge amount since Mazda recommended against them.

PS. I also use sythetics because Pettit recommends/recommended it

Kento

This is like the people who thought the world was flat because that's the way it appeared when they looked at the horizon. If the engine wasn't running right, there are a myriad other reasons for excessive deposits (not necessarily "carbon") in the combustion chamber. If you want to talk carbon deposits, why not take a look at pump fuel's somewhat high sulfur/ash content. Ever take a close look at the tailpipe, or even the internals of the muffler after several thousand miles on even a good running engine?

The oil deposits that David Beale refers to are due to a two-stroke motorcycle engine's relatively high oil/fuel intake mixture ratio (necessary because the ball bearing crankshaft depends on the intake mixture for its oil supply), and it's comparatively poor combustion characteristics at part-throttle/lower rpm settings.

People think that just because synthetic oil can withstand high temperatures better than dino oil that it "doesn't burn". Try heating a small amount with an acetylene torch and let us know what happens.

paw140

Here at school I have access to an instrument called a Thermogravimetric Analyzer (TGA). Basically you load up about 10 mg of a material, and it heats it up at a controlled rate in either an air or nitrogren atmosphere, and monitors weight loss. We use it mainly to test for thermal stability of various compounds.

Anyway, I'm thinking of running this on some Mobil 1 and a few dino oils that I have laying around the garage. The test results will give the thermal stability and the amount of carbon-black left over after heating. I think it would be interesting to see what the results are.

PVerdieck

Great idea, also get some Royal Purple and RedLine, or if you want, I can send you some RP.

Kento

Call or email Sport Rider Magazine and order the October 2003 issue. A Noack-derived test (basically the same type of test you are describing) was performed on various synthetic and dino oils with published results.