RotaryJay

I've had several RX-7's. I've been told be a lot of people that you should NEVER use synthetic oil in a rotary engine. The residue (supposedly) left by the synthetic oil after combustion in the engine will gradually destroy your apex seals, etc.

Has this changed with the renesis? If not, I can see a big problem with people using synthetics without knowing the possible damage it could do to the rotary!

If anyone knows, please tell!

Thanks,

Dazz

Having used either Mobil 1 Synthetic or Castrol Sythetic R in my engines for over 13 years, and having pulled apart many engines that have been run on synthetic all I can say is that it is absolute rubbish about synthetic oil in Rotaries causing problems.

People say it doesn't burn, well I had a worn out old 13B that used to smoke on start up quite badly (worn out oil control o-rings) until it warmed up, so if it wasn't the oil burning I don't know what it was.

The engine was a second hand import engine when I put it in my RX-2, I put about 90,000km's on it, sold it to a mate who put it in his car, and when we pulled it apart to do some porting, the rotors and housings were all in good condition with no carbon build up or anything to indicate synthetic oil related problems, and it was always run with Castrol Synthetic R and Mobil 1.

I would suggest people who claim some of these problems with synthetic are caused by other factors like running the engine too rich, and that is where the carbon build up is coming from.

ZoomZoom

Is it true that you should not use synthetic oils until the engine is fully broken in?

Quick_lude

This depends on the engine. On piston engines, usually if it is a small production performance engine like the Corvette, Porsche or if it is built to very close tolerances like BMW and Mercedes, those cars come with synthetic oil as OEM fill and owners are recommended to use synthetic.
I'm not rotor savvy enough to know how the rotary "breaks in" and if parts have to "set in" like in regular piston engines. On the 'regular' piston engines you should wait until about 5k Km and then you should be ok. I used synthetic on my Prelude from 6K, first oil change, and have not had any problems for 55K Km.

khoney

I've been running full synthetic (AMSOIL, Castol, Mobil1) in my 2nd gen since 1987. Still going strong at 145,000. And the best RX-7 mechanic in San Antonio advocates synthetic, too. I wouldn't be concerned about it. BTW, I wasn't as religious about oil changes as I should have been, sometimes going 10K between.

RotaryJay

Thanks for the replies... but I think I'll stick with non-synthetic to be safe. If the rumour about synthetics even arose in the first place, there must be a reason. I trust what everyone says, but I'm going to play it safe.

Maurice

I have always used synthetics in my pair of 7's. 1979 12A and a 1987 13B. Still running strong.

Dazz

If your going to be concerned about rumours then what about the ones that say the engines have to be rebuilt every year and if you don't warm them up for at least 10 minutes before moving they will blow up?

For warranty purposes I guess follow whatever Mazda recomend, but for me, after driving rotaries for the last 15 years I can say without a doubt that a good synthetic oil will do no harm to the engine.

MyT13B

I have used synthetic oils in my rotary engines since the first time I heard of them.


Most synthetics will handle the heat transfer much better than conventional oils.

The best part is that they do not break down like conventional oil.

SPDFRK

I am totally new to the rotary engine so I have no personal experience (I didn't know how they worked til I seen the QT movie on the website) but from what I have seen and can assume they are all oil injected and numerous arcticles are talking about how the renesis holds unburned hydrocarbons until the next combustion cycle to improve emmisions than can I conclude that there is a big opportunity for a conventional oil to be dilluted (break down) and allow them to be burned off, since a synthetic has a higher heat threshold and resists contamination better than dino than wouldn't they be less susceptible to this possible problem. If my theory is incorrect please feel free to ammend it or just call me stupid, like I said I'm a rookie.

wakeech

hmmm... ya, i can't argue against you Dazz, and Racing Beat also seems to unabashedly endorse synthetic oil use, but why would MAZDA itself only reccomend refined mineral oil?? not that i doubt your experience, but i'd just like to see scientific theory... just curious... there also might be a million other reasons that they wouldn't suggest using synthetics... i wouldn't know them though!! :D

Dazz

I would suggest that Mazda specify a good mineral oil, because it is cheaper as far as servicing costs go, and for the intended purpose of the car does the job entirely adequately.

Also, and I have had personal experience with this, anyone who has owned a rotary that has done a lot of kilometres, and I'm talking well over 160,000 where the oil control o-rings are starting to go, will be able to testify that even with synthetic oil, they will blow smoke, which is, you guessed it, oil burning!

And a quick question for you people. How much oil does the engine actually use during normal driving? Anyone care to guess .........

Even assuming oil use of say 250ml per 1,000km (RX-8 should be better than this) how much oil is that to be injected per revolution?

Well, I did a real quick and nasty estimate. Assuming your average speed in normal daily driving is 35km/h, and your average opperating rpm is about 2,500rpm, then per revoltion of both rotors, a total of 0.0001754ml of oil is injected into the engine!

So as you can see, it's not like you are pouring the oil into the engine in a large quantity.

Anyway, from my perspective, with over 15 years of owning, driving, racing and rebuilding rotaries I can say without a doubt that synthetic oil will not ruin the engine, will burn, and for extreme use will be better for the engine.

wakeech

ah ha!! evidence i can relate to. i am now a total believer...
hmmm... it WOULD be interesting to know how much carbon would be created from that amount of oil burnt... but that would mean on of us would be a chemist, with lots of assumptions... oh, never mind. :P

cool Dazz. i am converted.

Dazz

The other thing you have to remember, is that a percentage of carbon deposits are also caused by fuel not being burned properly.

I have seen quite a few engines that have been running cheap aftermarket efi computers that are not real good, and when the engines are stripped they are very carboned up, as well as showing abnormal signs of wear due to the overfuelling.

It's very easy to blame the "synthetic oil boogey man" for carbon buildups and all the rest, but in reality there are so many other factors that are responsible.

In my old 13B powered RX-2, which I used to drive pretty hard and race occasionally, I had adjusted the oil metering pump up a little higher just for a little added protection as it was an old engine to begin with. The car was running a 48ida Weber, which I spent a lot of time tuning to get the jetting as spot on as possible. This engine was always run on Casrtrol Synthetic R or Mobil 1 synthetic.

Now this 13B engine was a second hand import engine from Japan out of an RX-5, and was put into the RX-2 about 2 years before I bought it. In those two years the car did about 50,000 kilometres. I bought the car, and put another 40,000 or so on it, before pulling the engine out and putting it into my second RX-2. It was also fitted with the Weber at this point. It did about 15,000 in that car which was infortunately written off. But the engine was pulled out and put into my third RX-2. It did numerous track days and was my daily transport, and in the next two years did another 45,000k's.

So by now it had done about 150,000 kilometres + whatever it had done in Japan, and for at least 100,000k's it had synthetic oil in it. Now at this point, the engine was getting a little smokey, and was consuming a little more oil that it originally did. The fact that it was smokey indicated that the oil was indeed burning and not just carboning up inside the engine.

At this stage I pulled the engine out to replace it with a turbocharged 12A, and sold the 13B to a mate of mine who put it into an old rear wheel drive 323 hatchback. Now when putting the engine in, he had to swap the sump and pickup, and somehow forgot to put the new oil pickup onI When the sump was full of oil, there was enough oil to be picked up, but a few weeks later the engine seized due to no oil pressure as the oil level dropped just enough to stop the pump picking it up.

Anyway, we pulled the engine out and stripped it. It had picked up a stationary gear bearing, but was otherwise fine. But apart from that, and considering how many k's it had done, there was almost no carbon build up, nothing in the way of built up oil sludge or muck, or anything else to point towards any problems relating to oil.

In fact, the rotors and rotor housings were still in good enough condition to be put into an engine we built for his girlfriends RX-4, which ran 10.91@124.8mph, driven to and from the track in full street trim.

As far as maintainance went, I used to do an oil change about every 10-12,000k's, generally plugs at about the same time, and that was pretty much it. I would start the car in the morning, let it idle for about a minute then drive of normally until the engine was at normal operating temperature and then it was right to be thrashed. I generally never revved it over 8,000rpm, and after a good hard thrash would either just drive it gently before turning it off, or let it idle for about a minute just to let everything cool down a bit before switching it off, which is basically how I would treat any engine.

My turbocharged 12A has also been totally reliable in the same manner as the old 13B, and has also been run on Mobil 1 synthetic. So for me, I can see no reason why not to run synthetic in a rotary.