Kento

If you're referring to the combustion by-products of current synthetic oils (the heat in the combustion chamber is high enough to burn any oil that enters the combustion chamber), the answer is no. Early synthetic oils (as in the 1970s and 80s) had a high phosphorous content (phosphorous is an anti-wear additive), but it was found to be harmful to the long-term life of catylyzers, so they cut the phosphorous content down, and used other agents for anti-wear properties.

dgeesaman

iTrader: (7)

OK, thanks. I translated that good stuff to mean it basically all burns in the chamber nowadays

BLKTOPTRVL

Since you didn't understand, I will restate...

What I am saying is that a rotary injects oil for the purpose of lubricating the seals and springs. The reason it is injected is because there is no opening to the pan - as in piston engines - that will allow the crank and piston skirt to splash the lubricating oil around.

There is no NEED TO BURN THE OIL. The oil is burned as a side effect of being in the combustion chamber when the plug is fired.

I stated this as a question because I know that I do not know everything and was inviting somone who knows more to comment. So...

UNLESS SOMEONE KNOWS OF A DIRECT REASON THE OIL NEEDS TO BURN (I know of none), IT DOES NOT MATTER IF SYNTHETIC OIL WILL OR WILL NOT BURN.

Kento

Sorry, should have stated my previous post more clearly: the heat generated by combustion in the combustion chamber is hot enough to burn any oil droplets in the intake charge (unless you're running some ungodly high mix ratio like that required for two-stroke engines) that haven't condensed on the rotor housing walls/rotor/seals during the intake phase. There is also some burning/evaporation of the oil film on these components during each combustion phase as well, but as for how much, I'm not sure.

So yes, any oil needs to be combustible to a certain extent, otherwise enough would eventually be forced out through the exhaust ports to clog up the catalytic converter.

BLKTOPTRVL

I think you may be quoting the wrong person...

But anyway, to paraphrase, you are saying that the volume of oil needed to lubricate and cool the engine, then needs to be burned so that it does not all end up in the converters? The reason it is burned is so that the volume exiting is lowered?

Kento

You're getting a little involved in semantics here. I don't know where you got the "volume of oil needed to lubricate and cool the engine, then needs to be burned...." from. It's not the "reason it is burned". Oil needs to be combustible in some way; for instance, the oil control rings in a conventional engine don't last forever, so the oil manufacturers must take that into account, lest it clog up the combustion chamber, exhaust ports, valves, etc. after extended periods. Otherwise, why not just use a lubrication medium that lasts forever?

edit: I'm just replying to your "unless someone can tell me a reason for oil to burn" question. No worries.

adam c

iTrader: (2)

I believe that synthetic oil reduces friction better than conventional oil. I have no proof of that, that just what I believe.

I know that synthetic oil runs cooler than conventional oil because I did my own test. I posted the results on this forum, but was unable to find them with the search function. Anyway, I started my car and let it idle. I wrote down water temps and corresponding oil temps with Castrol 20/50 oil up to 220 degrees. I let the car cool for a few hours, and changed the oil to Mobil1 15/50. I performed the same test, and found that the Mobil1 consistently ran at least 10 degrees cooler than the Castrol.

SpeedKing

iTrader: (4)

Was this "test" done strictly at idle? Did you measure oil temps. at speed? And what was the timeframe given?

Anyway, more relevant would be to have an oil analysis done with both regular and synthetic oil.

http://www.blackstone-labs.com/

Kento

It wouldn't necessarily be more relevant, because then you'd have to control the absolute conditions of the vehicle/engine it was used in. And even then, spectrographic analysis of an oil can only give you basics of oil performance: before/after TBN, acidic neutrality, various compound content, etc. Anything else is just very nebulous "clues" as to what's happening. And much of this information can be liable to subjective interpretation anyway, just like the whole synthetic/dino debate in the first place.

adam c

iTrader: (2)

The test was as I described, at idle. The timeframe was about 4 hours between tests. Plenty of time for the engine to completely cool off between tests.

I don't claim that my test was in perfect "laboratory" conditions. Actually, it was in my garage I understand that the test is limited in spectrum. You may interpret the results as you please.

SpeedKing

iTrader: (4)

Running regular oil for 3 months under normal driving conditions then doing the same with synthetic and comparing results is more relevant than changing oil and checking oil temps after letting your car idle for 15 min., don't you think? I didn't want to be too harsh on "adam c" because his "test" sounds like something "ZeroBanger" would do.

BLKTOPTRVL

OK.

adam c

iTrader: (2)

This was to be a simple test. I was not willing to do a long drawn out test. It was quick, and easy to do, so I did it, and posted the results. It is not my responsibility to prove anything to anyone. Perhaps you should do your own test. I'm sure that you have the perfect conditions, time, equipment, and money to perform a test that no one will question

As I already stated, it's not a full spectrum test. Interpret the results as you please.

Kento

Yes, but only slightly. You cannot control all the atmospheric and driving conditions within those 3 months, which will definitely affect how the spectrographic readings come out.

Ouch...

13Beast REW

I ran my car with Mobil 1 for 25,000 miles then switched back to fossil. I actually notice cooler temps with Valvoline VR-1 20w 50 than with the Mobil 1. This is in south Florida and I'm not an oil guru or anything so I dont know if anyone in colder temps and/or less humidity would experience the same results but I'm goin Valvoline VR-1 until somethin better comes along.

spyfish007

If you take apart a motor that has run synthetic oil vs. regular oil, you will see a larger amount of deposits on the rotor. After a long period of time these deposits will in fact raise the compression of the engine. I'm not saying a huge difference, but a difference none the less. Could that difference be enough to detonate the engine ... maybe if things go bad enough.

DamonB

Just to be clear, which oil leaves the most deposits?

TracyRX7

If it does do anything it doesn't raise any of the measured emissions in a CA smog test (raise them over the legal levels anyways, not sure if my measurements would be lower in the good range on a conventional oil). The motor in my car has been running Mobil 1 (10W30) for about 33k miles now since a rebuild and all seems to be running well for now.

Mahjik

iTrader: (1)

I think he is saying synthetic leaves more deposits. Here's recent post:

PVerdieck

NO. Not the entire volume of oil, just a portion of it, but all the oil in that volume must combust clean.


Oil serves two purposes in a rotary engine.

1) Standard usage, transfer heat from engine as it flows through the oil passages. This oil, per se, doesn't need to burn.

2) Rotary usage. A small amount is leeched from the oil system into the Oil Metering Pump. This oil is mixed with gasoline which is used to lubricate the Apex Seals at the rotor tips. This oil & gas is then used for cumbustion. Thus this oil needs to combust clean. Otherwise carbon buildup on the rotor housings will eventually cause other problems.

Thus the engine oil in the rotary needs to be combustable.

Now this can be changed. If one rips out the Oil Metering Pump and installs a Reservoir (which I will do when my OMP dies), then you could run TCW III synthetic in the reservoir, and whatever else you want in the engine.

PVerdieck

This is a constantly changing target.

What happened is that some early (1st gen) synthetics had horrible ashing, and that led to Mazda's infamous "no synthetics in rotaries" policy. Since then, further development of synthetics has produced cleaner burning oils. But in the beginning, the dinos burned cleaner.

In general, I think synthetics have all gotten cleaner. If you look at the link on the first page, More then you ever wanted to know about oil , then you will see ash content.

This is old data though, so there have been changes.

A great synthetic, is what I premix with. Synthetic 2 cycle oil (TCW-III). This type of oil is designed from day one to burn, so it should have some of the lowest ash/carbon post-combustion deposit levels. This is also basically what Pettits Pro-Tek R is, just another brand.

I use Royal Purple 10W-30, because I found low ash numbers for it, and Rotary Performance loves it, and, in general, Pettit recommends synthetics for performance reasons, although they cost a lot.

spyfish007

Yeah, I wasn't too clear on that one. Synthetic seams to leave much more build up on the rotor and convential motor oil.

spyfish007

Oh yeah, another problem that adds to what I am talking about--tuning. Some people have tuning that is so !#$# rich and the timing is off and leaves more build up on the rotor too.

Kento

In a nutshell. The synthetics have progressed far beyond the early formulas. And yes, that old listing has been regurgitated countless times by various sites.

There are other issues that are contributing to the excessive combustion chamber deposits that spyfish has seen.

adam c

iTrader: (2)

For what its worth, Pineapple Racing also recommends using synthetic oil.