Thanks for that link, Conundrum.

I find it interesting that Mazda dealerships are using synthetic or synthetic blend oils, given that statement by Mazda.

This is really an interesting and confusing issue.

Since I'm changing the oil every 3,500 miles (and replacing a quart between oil changes), am I really getting any of the benefits of using synthetic? How much better is new synthetic than new dino? Enough to justify the cost and the "unknown" long term effects?

This answers your questions...

If you don't want to take any chances with Mazda voiding your warranty, stick with premium and dino oil.. Should something happen they most likely will find ANY excuse to blame it on you.

That being said.. In my climate, 87 routinely detonates (sounds like a fan belt squeal) at high RPMs. 89 runs fine, but I run only premium now because I had fouled plugs (random misfire) once and the dealership blamed the 89octane, even though I explained to them that I had been driving around at 5mph for 4 hours looking for a lost cat. The driving at low speeds/rpms was most likely the reason for the fouling, but I run 93 to take no chances now.

Just a note- I have filled up with 89 octane twice. I could actually feel a performance difference over 6k rpm, and I actually got worse fuel economy. Because of this, I see no reason to save a paltry 3.33% a gallon by using mid grade over high test.

The oil issue is based on the actual burning characteristics of the synthetic instead of the lubrication properties in the engine. Remember, the engine actually injects engine oil into the intake. The question is- does synthetic burn off better or worse than regular oil? Even though it would not be good for the public image of the rotary engine's higher maintenance issues, it would have been nice if they would have had a different oil container for the injected oil so we could use synthetic in the engine, and two stroke in the intake.

I'm taking no chances with my vehicle.

I'm sticking to the the manual, strictly, from day 1 of ownership, until the day I sell it.

That means 91 octane fuel, and SAE 5W-20 oil bearing the quality rating SL or ILSAC.

I drive my vehicles gently, and don't plan on doing any modifications whatsoever during the warranty period.

I would NOT recommend to anyone else to use synthetic oil if they absolutely did not want to void their warrenty; the same as I would not recommmend to the same person to go FI.

:Start Rant: BUT... it is a logical fallacy to suggest that synthetic oil is somehow bad for the 8 because Mazda does not recommend it or because it is "Unnatural". Synthetic oil is just that; oil that was synthesized. It's 'polymer chains' are the same combinations of carbon and hydrogen in dino oil and so it burns and it mixes the same (more or less). They dont recommmend it because they do not want to spend the time and money to go back and run this engine 1e7 hours with synthetic to make sure that they can recommend it. It is just cheaper not to recommend it.

SO, I would hate to see someone read this the title of this thread and think that the above quote was anywhere in the vicinity of fact. That quote is based on the same logic as why the "Turbonator" works. (it does not work, BTW) It is the same arguement as why you should use Natural chemicals instead of Synthetic. A chemical is a chemical. It does not have some vital force just because it was made "naturally" Next we will be asked to believe in spontanious generation.

:Stop rant:

Why?
 

Why would you want to use MORE EXPENSIVE oil, when you have a car that is SPECIFICALLY designed to CONSUME oil? I don't understand why you all think that you know better than the engineers that designed this car.....other automakers like BMW put synthetics in the car at delivery, Mazda says not to use it. The owner's manual is the ultimate guide, it is written by the company that designed and built your car....why would you want to save a couple of cents on gas to use a lower grade BUT then spend MORE to buy synthetic oil....NO LOGIC TO ME! :confused:

i can not believe how big of a debate this is. no one is telling anyone to use synthetic.

in my car, i have used nothing other than 93 octane for 14,000 miles. i just recenlty switched to full synthetic, as after reading the owners manual, warranty booklet, extensive searching on this forum and elsewhere on the internet, i have come to the personal conclusion that synthetic will work just fine in my rx-8.

if you read my previous post in this thread, you will notice that i scanned the page out of the owners manual that covers what type of oil to use. you will notice that there is absolutely no mention at all of synthetic here. this means (my interpretation) that as long as the recommendations of mazda are met (5w20, ilsac or sl certification) then oiil choice is up to the consumer.

as to the motor consuming oil, i feel that a synthetic is a much better choice, as the hydrocarbon molecules are going to be more uniform than dino, so should burn better during the combustion process, leaving far less deposits behind, having higher tolerance to heat (and we all know that the rotary gets very hot, and that about 1/2 of the cooling is done through the oil coolers), better lubricity, and having better basestock to start with, less additives such as paraffin, which is basically a wax, which i am sure we all know, that when wax gets cold, what happens.

AGAIN, THIS IS MY OPINION. THIS IS NOT MY ATTEMPT TO SWAY ANYONE TO ONE SIDE OR THE OTHER ON THIS DEBATE.

To the original poster.
Trust you got your answer to these 'simple' questions?

Lots of questions do not have that black & white answer. Go with your best educated guess.

For me, the 1st 10,000 miles I chose 93 octane, either Texaco or Shell. The last 23,000 miles have changed to 87 octane. I have noticed no appreciable difference in performance, have experienced no pinging, but did pick up 2 mpg.

Changing my oil every 2,500 miles; as a result I have chosen to use a mineral-based oil; Castrol GTX 5W-30. Living in Alabama, the high heat & humidity rivaled other countries where Mazda uses 5W-30, not 5W-20. I just felt more comfortable with this weight.

The next oil change will be given a UOA (Used Oil Analysis), and subsequent changes thereafter, to check progress of wear. I suggest if you are concerned whether your oil choice is correct, you do the same.

Just a note- driving a vehicle too gently can actually be bad for it as it allows carbon to build up in the engine. This is especially true with rotary engines.

The short of it- give the drive train at least 1000 miles to break in before revving close to red line, and also play it safe with the brakes and clutch to let the wear surfaces break in. Also allow the engine to warm up a few minutes before revving it beyond needed normal power (4-5k rpm).

But past that, this engine is designed to rev. But driving hard doesn't mean abuse. You shift quickly but without forcing the tranny to move quicker than it wants to, and always keep watch of all the fluid levels and changing requirements. Also, running an engine very very hard then sliding to a stop and shutting off the engine is not good for the oil left in the engine.<- That is actually a turbo engine note, but since the Renesis runs so hot, it probably applies here too.

I have owned many vehicles and many Mazdas. I drive them hard, but do not abuse them and I keep them properly serviced. That is why I buy vehicles- to enjoy driving. Now if I was buying them expecting the vehicle to last for 20 years, I would probably driver them differently. But then I would not get that smile tattooed on my face....