Which Oil type?
 

I'm about to do my first oil change and have been reading practically all the threads regarding the oil to use in the RX8. I must say that after reading all the expert opinions I am now more confused as there seems to be no consensus as to which is the better oil type, although there is a leaning towards mineral oil.

I am counting on this poll to help me decide on which oil type to use.

Dinosaur oil. Mazda recommends it, and it's cheap so you might as well change it every 3k miles.

There's absolutely no question as to which oil is better oil - synthetic. By any possible test or measurable parameter, synthetic oil beats dino oil.

For non-Renesis engines, the question is "can you justify the additional cost of synthetic for the better protection and durability of synthetics?"

For Renesis - the question is do you believe the people who insist that synthetics should never be used because their dealer's service department said so? Do you believe the RX-8 Owners Manual, which only specifies oils meeting API SL specification and says absolutely nothing about synth pro or con? (To rephrase - the RX-8 Owners Manual does NOT prohibit the use of synthetic oil, as long as that synthetic oil meets API SL).

My take - API SL is API SL. The RX-7 93-96 Manual specifically prohibited synthetic oil - the RX-8 does not. The worries that "synthetic doesn't burn as clean" are nonsense. Further, the oil change volume (~4 litres) is just over half the total volume of the oil system, meaning an oil change is only replacing half the old oil. The extended life capability of synthetics is valuable in this scenario. I use Castrol Syntec oil. To help justify this - if you really know your synthetics, you know there was a debate a few years back where Mobil sued Castrol for false advertising, saying that since Syntec wasn't made from the pure synthetic PAO base stock but was just ultra-refined and re-formed crude oil, that it couldn't be called synthetic. The judge ruled that since it was more refined than regular crude-based oil, and had similar charactieristics to synthetic, that it could legally be labelled synthetic. What it comes down to is: IF Mazda didn't want you to use synthetic because of some characteristics of PAO-based synthetics, then Castrol Syntec is exempt from that worry, and thus is safe to use anyway because it's really just an ultra-refined dino oil.

Regards,
Gordon

I use sysnthetic blend - Motorcraft 5w20. The use of a full synthetic (as I use in my other 2 vehicles) is not warranted here and possibly could be bad. Anyway, since only a little over half the oil is changed each time. full synthetic would be a waste. I will use full synthetic in the transmission and rear end.

Just wanted to chime in, and say that I have gotten more out of using 5w-30 than 20 in my 8. It seems to last longer for some undetermined reason.

Mazda has now given their blessing for use of synthetic oil.
The use of synthetic oil is almost 100 % in racing.
The Mazda rotary that won the 24 hours of LeMans was of course using synthetic oil.
Almost all new high-end cars are now being filled with synthetic from the factory......I know, I know what about it burning in the combustion process.....Mazda now thinks it's a good idea.....less warranty work in the future.

Kind regards,
DG

Just as I thought, there will never be a consensus as to which is better. Perhaps it would be wiser to go with the flow and use dino oil (overwhelming majority).

So, does that imply that the lighter-weighted oil (5w-20) burns better and thus cleaner? My apologies if this is a silly question.

Check the post by Gyro right at the bottom of the page. The drivers guide specifies "Add only non-synthetic 5W-20 engine oil...". So Dyno oil it will be.

https://www.rx8club.com/showthread.p...n&pagenumber=2

"When in doubt, go with the flow"

Or if you want absolutely the best oil, buy the Enzo's required $60/L oil or Racing Beat's special Rotary Oil that's almost as expensive :p

Seriously now, I'm planning to use synthetic but still don't know which one. Castrol seems fine not being a "real" synthetic but I'm also thinking about Redline or Royal Purple.

What I'd really like to do is have an independent metering oil container like the mod at rotaryaviation. Then I'd use pure synthetic in the engine and 2-cycle synthetic in the metering oil tank.

Personally, I use the dino-oil. Today's oils are SO good compared to years ago, and changing it regularly, all makes me very comfortable. Also, I would NOT use the heavier 5/30 oil. Remember that oil is INJECTED into these engines to lubricate apex seals, etc. A heavier oil won't spray as efficiently, so may compromise lubrication. Even though a heavier oil will help to maintain pressure, it does so at the expense of flow. I'm sticking with the 5/20 to get the pressure, flow and spray volume that Mazda designed for.

It's worth noting that outside of North America, Mazda does specify 5W30 oil for the Renesis in the RX-8. It's only here in the US and Canada where 5W20 is specified.

That would by my last criteria for selecting a motor oil! Why on earth would you assume that the majority know what they're talking about?! ;) It's a bit more work, but I always try to figure out who the real experts are, and then I'll listen to their opinions and advice. Also figure out who the, uh, less technically educated or informed are, and then be sure to discard their advice! :D

Regards,
Gordon

Thanks for your honest opinion Gord.
On Who wants to be a millionaire, when contestants ask the audience, they usually get the correct answer. Hehe.
More seriously, I assume that most owners have done research of their own and have weighed the opinions of pro-synthetic against those of pro-dino, and have made up their mind in a rational manner. Since the poll is showing a 10:1 preference for dino oil, it makes my decision an easy one.

And Mazda themselves, in their driver's guide, recommends dino oil. Anyway, IMO either type of oil would not be harmful to the engine and the difference in performance and reliability, if any, would be very minimal.

The dealership told me never to put Synthetic oil in it. They had this long explanation, it got over my head. But do any of you guys know what it was? I'm sure some of you may have heard this from you dealership too.

Using AMSOIL XL-7500 5W-20 synthetic. It meets all requirements specified in the RX-8 owner's manual, and my previous rotary history with synthetic has been good.

I'm going with Castrol GTX magnatec 5w30 here in the UK; it's the only non-synthetic (i.e. semi-synthetic) 5w30 I can readily lay my hands on. Can't seem to find a dino 5w30 over here ... anyone any ideas?

This debate has been going on for TWENTY-ONE Years!!

Sep 20, 1983... Oct 8, 1984

These archive posts are really the start of the "synthetics aren't good for rotaries" debates on the internet. . . and as you can see by the posts, what was said back then is said now.

So, if you must use synthetic, please do your own homework about the oil you want to use.

Synthetic oil is ok
 

The real reason it is ok to use synthetic oil is that the Renesis engine injects just a fraction of the oil the older rotary engines did. (less pollution)

The owners manual does not say do not use this type of oil.
Mazda has now said it is ok!

Use synthetic oil it really is the best.
Reduced Oil Consumption
In a rotary engine, oil is supplied directly to the interior walls of the combustion chamber to lubricate the "apex" and "corner" seals. Engineers kept the paths which supply oil in the RENESIS as small as possible, and we have redesigned the oil supply nozzles to improve their efficiency. With these enhancements, the RENESIS consumes about half as much oil as a conventional rotary engine.

On the Pennzoil oil I bought it does not say anywhere if it is synthetic or non synthetic? How can I tell? I used the weight suggested in the manual.

If it doesn't say "synthetic" it's not. Pennzoil has the word "synthetic" written right across the front of the bottle, in big type.

You changing your own oil?

No, just adding some for the first time.....has not needed it and had an oil change at the dealer early on since I saw some sludge in it. The front says nothing on my oil....so I guess it's not synthetic. ok.