The reason that rotaries and synths don't mix is the huge 'O' rings around the housings - early ester and amine based oils would eat Buna N and Viton for breakfast.

First generation Mobil 1 was the oil that ate the seals out of my first rotary, in 1976.

Easiest for Mazda to just say 'no synths'....

 

cool... another oil debate!

 

Nope. No debate. Stealth nailed it.

 

Yeah, while my recent failure (coolant seal) was no fault of the oil I use (Mobil1), I will probably just run Castrol GTX 40W in the new one since the one motor i did have that made it to 74,000 ran Castrol GTX 10W-30.

 

^^ Agreed (with MM), the point of this thread was for me to just get edumakated on exactly where carbon forms just so I can understand why the heck I am redlining my car everyday (not that I am complaining lol)